Hello,
I've been reading through this forum for a while, studying, and trying to learn as much as possible about my SD25 engine. What a wealth of knowledge. I'm no mechanic, so bear with me, I might butcher some terminology.
I have an SD25 in my 1973 Series 3 Land Rover, and it's been quite a nice upgrade from the original diesel engine. If you think the SD engines are gutless, you ain't seen nothing....you can get overtaken by old men on bicycles running the original land rover diesel engine.
The vehicle still has the original 4 speed gearbox and transfer case. I mounted a mitsubishi turbo, the TC05-12a, after reading through some good advice on this board. No intercooler installed. I would max boost at around 8psi, and I had the wastegate shortened almost to the limit to promote boost. If I adjusted the wastegate tension to allow it to open under less pressure, I would lose considerable boost. With very little adjustment on the wastegate I'd be maxing out at 3psi, which I thought was pretty lame for boost. Hence, I tried to keep the wastegate with as much tension as possible.
For 6 months I was ok, no real issues. Last week, my engine locked up....cracked piston. bad news. i was running standard pistons, nothing ceramic coated or aftermarket. For the last month leading up to this event, there were warning signs that I could not address in time to prevent this disaster. I was losing water, and running hotter than normal. The radiator was fine, I couldn't find any water leaks. I took the vehicle to a local mechanic for troubleshooting (keep in mind I live in a 3rd world country where anyone with a wrench is a "mechanic"), and the mechanic could not identify any major issues. So off I went until disaster struck.
My main question is what most likely caused my cracked piston? I thought 7-8psi on these engines would not be an issue, but I think my turbo setup is what caused this. Should I limit the turbo to 3-4psi?
Also, keep in mind that my gearbox is geared very low. These vehicles were made to climb trees, not cruise modern highways. Nevertheless, part of my reasoning for installing an SD25 engine was to allow the vehicle to cruise on the highway under less stress. This vehicle does not have a tachometer, but at 55-60mph i'm wound out (not sure of rpm).
Is the combination of high rpm and 7-8psi of boost too much for this engine to handle? I'm probably going to make the investment to rebuild the engine, but what considerations to I need to make? I don't measure EGT, but that's certainly something that I will have on the next go round.
Any insight would be most helpful.
Cheers!
Dan C
SD25 Turbo Blues
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dc1184
- Posts: 17
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- Location: Costa Rica
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ehtrain
- Posts: 144
- Joined: 12 years ago
- Location: regina, sk
im interested to see what you find out. I'm still interested in turboing my sd25 with a ve pump. but as far as anyone I've managed to talk to in australia these motors sound pretty reliable with 8psi or less. With no EGT on board and playing with the fuel screw seems like ud be asking for something to go wrong tho.
they did make a couple versions of the sd25 though. 61-83 had fabric headgakets, 83-91 had metal headgaskets. not sure if there is a year split but the stationary motor was a 5 ring piston I'm pretty sure with no "alfin" steel compression ring insert. while the truck motor had the "alfin" which is more common on turbo diesel. my 87 also has piston oil cooling jets.... id imagine the older ones would as well. Someone had told me they had a book or magazine referring to cylinder head port differences in various years. I have a forklift head on my truck block. I maybe lucked out but its the same as the truck. I have yet to find factory casting info though to find out if there is a physical difference possibly in pre chamber sizing.
as for cracked pistons... so far I've seen ether starting fluid do it. if your in a warmer climate that would seem more unlikly though.
they did make a couple versions of the sd25 though. 61-83 had fabric headgakets, 83-91 had metal headgaskets. not sure if there is a year split but the stationary motor was a 5 ring piston I'm pretty sure with no "alfin" steel compression ring insert. while the truck motor had the "alfin" which is more common on turbo diesel. my 87 also has piston oil cooling jets.... id imagine the older ones would as well. Someone had told me they had a book or magazine referring to cylinder head port differences in various years. I have a forklift head on my truck block. I maybe lucked out but its the same as the truck. I have yet to find factory casting info though to find out if there is a physical difference possibly in pre chamber sizing.
as for cracked pistons... so far I've seen ether starting fluid do it. if your in a warmer climate that would seem more unlikly though.
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dc1184
- Posts: 17
- Joined: 11 years ago
- Location: Costa Rica
ok, I'm making progress. we got the engine disassembled, and one piston was cracked all the way down the sidewall and the top looked totally smashed/deformed. The other 3 pistons look to be in great shape.
Also, my pistons are all 3 ring pistons, is that a problem? I forgot to look for oil jets below the cylinders but i'll have a look tomorrow. Also, my head was cracked in two spots, the famous weak points between exhaust and intake valves. There is a small crack between two of them, so I purchased a new head. Interesting to note, the packaging on the new head reads "for nissan sd23/25". I thought the heads were different between the 23 and 25, but the way that my new head is labeled makes me think otherwise.
I'm going to have the engine rebuilt. It will encompass 1 new piston, 2 new valves (the 2 corresponding valves from the destroyed piston were shot), valve seals, complete gasket set, new set of rings, new bearings, assembly, and away we go! A local machine shop polished the crankshaft, and it was in fine shape to begin with. Also the cylinder wall was a bit scored from the damaged piston, and that was repaired.
At this point, I'm not really sure if the turbo even caused my problems. I was expecting to see issues with all of the pistons, but that was not the case.
If anyone has any good advice before the engine gets assembled, let me know.
Cheers!
Dan C
Also, my pistons are all 3 ring pistons, is that a problem? I forgot to look for oil jets below the cylinders but i'll have a look tomorrow. Also, my head was cracked in two spots, the famous weak points between exhaust and intake valves. There is a small crack between two of them, so I purchased a new head. Interesting to note, the packaging on the new head reads "for nissan sd23/25". I thought the heads were different between the 23 and 25, but the way that my new head is labeled makes me think otherwise.
I'm going to have the engine rebuilt. It will encompass 1 new piston, 2 new valves (the 2 corresponding valves from the destroyed piston were shot), valve seals, complete gasket set, new set of rings, new bearings, assembly, and away we go! A local machine shop polished the crankshaft, and it was in fine shape to begin with. Also the cylinder wall was a bit scored from the damaged piston, and that was repaired.
At this point, I'm not really sure if the turbo even caused my problems. I was expecting to see issues with all of the pistons, but that was not the case.
If anyone has any good advice before the engine gets assembled, let me know.
Cheers!
Dan C
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ehtrain
- Posts: 144
- Joined: 12 years ago
- Location: regina, sk
hmm that sounds like a lot of damage inside. More then some high boost. That sounds more like bad overheating or maybe was hydrolocked. but hydrolock on diesel tends to break lots with such small clearances.
I remember reading somewhere the valve diameter was smaller on the sd23. something like 2mm on each valve. I will see what info I can dig up. so in theory an sd25 head would work for both. where did you purchase a new head from if you don't mind me asking?
if your rebuilding with 1 new piston. make double sure your checking your ring land gaps on the old pistons vs the new ones. it may not be worn much but it will make a difference in longevity IMO. Also weigh the pistons. old vs new. make sure they are similar in weight. If one piston is abit heavier then the others it will throw the bottom end balance out slightly. Could be minor or fatal depending.
also check the top ring land for the steel ring insert or "alfin". I also found my block had a convenient drain port mysteriously under the area where a turbo would nicely fit.
if you want some good advice if you can fit or make the metal headgasket fit. do it. On race cars and anything high boost a multilayered metal headgasket is usually a must.
also if you have your motor apart why not get your injectors and injection pump serviced if there is someone reliable? they could also set you up for boost. You will also need to set your injection pump timing after it's been apart. check my thread http://nissandiesel.dyndns.org/viewtopic.php?t=2923
last post I found some timing info if you cant find any. If you can I would appreciate if you shared any info on the fuel system you can find or have.
I remember reading somewhere the valve diameter was smaller on the sd23. something like 2mm on each valve. I will see what info I can dig up. so in theory an sd25 head would work for both. where did you purchase a new head from if you don't mind me asking?
if your rebuilding with 1 new piston. make double sure your checking your ring land gaps on the old pistons vs the new ones. it may not be worn much but it will make a difference in longevity IMO. Also weigh the pistons. old vs new. make sure they are similar in weight. If one piston is abit heavier then the others it will throw the bottom end balance out slightly. Could be minor or fatal depending.
also check the top ring land for the steel ring insert or "alfin". I also found my block had a convenient drain port mysteriously under the area where a turbo would nicely fit.
if you want some good advice if you can fit or make the metal headgasket fit. do it. On race cars and anything high boost a multilayered metal headgasket is usually a must.
also if you have your motor apart why not get your injectors and injection pump serviced if there is someone reliable? they could also set you up for boost. You will also need to set your injection pump timing after it's been apart. check my thread http://nissandiesel.dyndns.org/viewtopic.php?t=2923
last post I found some timing info if you cant find any. If you can I would appreciate if you shared any info on the fuel system you can find or have.
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dc1184
- Posts: 17
- Joined: 11 years ago
- Location: Costa Rica
hey, thanks alot for the advice. I definitely think overheating was an issue, but is it fair to say that overheating could have been caused by too much turbo? Perhaps my wastegate being almost completely shut off contributed to the overheating?
I got the new head from the local nissan dealer here. $550.
Can you please clarify a few things, if you don't mind. "Ring land gaps", not sure exactly what that means, but I'm guessing those are the grooves where the rings sit.
A metal headgasket might be tough to find. I ordered a complete gasket set which includes a headgasket, and it's highly unlikely that it will come with the metal one.
It's kind of humorous that I would need a racing-style headgasket for a vehicle that maxes out at 60mph....that's downhill, downwind. I'm going to set the max boost to 5psi.
My pump and injectors were rebuilt in the last year. I'll take it to get setup correctly for the timing and turbo. Those injection pumps weren't made for turbo, and the way understand the setup is as such:
- it's either going to be a little rich at idle so as to provide enough fuel at boost
- or set properly at idle, will be a little lean on fuel at boost
Cheers!
Dan C
I got the new head from the local nissan dealer here. $550.
Can you please clarify a few things, if you don't mind. "Ring land gaps", not sure exactly what that means, but I'm guessing those are the grooves where the rings sit.
A metal headgasket might be tough to find. I ordered a complete gasket set which includes a headgasket, and it's highly unlikely that it will come with the metal one.
It's kind of humorous that I would need a racing-style headgasket for a vehicle that maxes out at 60mph....that's downhill, downwind. I'm going to set the max boost to 5psi.
My pump and injectors were rebuilt in the last year. I'll take it to get setup correctly for the timing and turbo. Those injection pumps weren't made for turbo, and the way understand the setup is as such:
- it's either going to be a little rich at idle so as to provide enough fuel at boost
- or set properly at idle, will be a little lean on fuel at boost
Cheers!
Dan C
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ehtrain
- Posts: 144
- Joined: 12 years ago
- Location: regina, sk
well i suppose you could see an overheating symptom pretty easy if you have high egt. Hard to say though if you'd see head cracks from it over a blown headgasket or maybe a burnt valve? But I currently don't have enough knowledge on egt's with fuel rates as my truck is my first diesel modification adventure. maybe someone else can chime in better on that one.
wow that's an amazing price for a brand new dealer cylinder head. dealers up here showed discontinued, and australia parts guy quoted from 770-1200 from reconditioned to brand new and blank. (no valves or guides, just pre chambers)
and yes you guessed right about the ring land gap. As a piston travels up and down the rings actually will twist slightly in there "ring land" there is a measurement limit in the manual for this I believe. But over time and wear, and your case boost. the rings tend to take a lot of punishment as they are always twisting and rotating to clear carbon and make the compression seal/oil scrape. thats why crosshatching is very important during break in to get the rings moving.
the steel piston ring insert helps the compression ring (top ring) take more abuse and last longer under boost conditions as there is a large cylinder pressure increase.
thats also very good news about the metal headgasket. I was wondering if nissan would just update the kit period and just negate the old fabric gaskets. when I reffer to race vehicles gas engines take a lot more to make the type of cylinder pressure as diesel makes stock. naturally a diesel needs to be build heavier as your compression is about 4-500psi where as a gas engine would be about 150psi. so there is a lot more force working against the pistons and bottom end of a diesel as it is, without adding the turbo. So no your truck isn't "race" but your engine requires every bit of its strength to hold that compression inside and the resulting force of the power cycle. "built" doesnt have to mean race lol.
your guess on the injection pump is what I have basicly understood as well. But dodge/volkswagon and a few other company's used boost compensators on the same/similar pump. So I've been thinking of trying to find another pump with the compensator and see what can be done. I found a blow up diagram from nissan with both boost/altitude compensation built in. So makes me think maybe the newer td25 or td27 used a similar injection pump with the boost parts already installed. but if im remembering right its the pump head that's calibrated for the motors fuel requirements. so im pretty sure a 2.7 wouldn't work on a 2.5 without the metering recalibration. I just pulled all my old school books out and started reading again to refresh myself as I have been having issues with my truck and fueling.
I've been thinking about boost levels too. I'd probably stay like your suggestion. I was think 5-8psi max. just enough to recover any horse power im already loosing and maybe a touch more. Id rather no smoke and some boost then screwing with the fuel screw a bunch. To me reliability/longevity is most important.
also if you said u could only build 3 psi boost with the wastegate set correctly. maybe your turbo is too big? when I started doing boost figure calculations vs cfm flow. I found my 1.8l nissan gas turbo worked nicely according to some flow maps I found. I was actually quiet surprised how small a turbo this motor would require even to touch 150hp. which seems dreamy from a little bit of boost. I also did map figures for an sr20 nissan (2L gas) and the turbo was actually quiet large and it would seem the diesel would barily touch anything worth looking at on its effecientcy scale. I also was thinking about a toyota surf/helux turbo. as the 2.4l would have simiar needs for boost. I did abit of googling awhile back and found a newer nissan xtrail diesel had a nice diameter turbo with ball bearing turbo that would meet the right mapping for our older fuel systems.
remember newer diesels run higher boost and typically run direct injection so there air requirements are different. I have also though about a variable geometry turbo.... but they aren't so easy to just "find" here. lol
wow that's an amazing price for a brand new dealer cylinder head. dealers up here showed discontinued, and australia parts guy quoted from 770-1200 from reconditioned to brand new and blank. (no valves or guides, just pre chambers)
and yes you guessed right about the ring land gap. As a piston travels up and down the rings actually will twist slightly in there "ring land" there is a measurement limit in the manual for this I believe. But over time and wear, and your case boost. the rings tend to take a lot of punishment as they are always twisting and rotating to clear carbon and make the compression seal/oil scrape. thats why crosshatching is very important during break in to get the rings moving.
the steel piston ring insert helps the compression ring (top ring) take more abuse and last longer under boost conditions as there is a large cylinder pressure increase.
thats also very good news about the metal headgasket. I was wondering if nissan would just update the kit period and just negate the old fabric gaskets. when I reffer to race vehicles gas engines take a lot more to make the type of cylinder pressure as diesel makes stock. naturally a diesel needs to be build heavier as your compression is about 4-500psi where as a gas engine would be about 150psi. so there is a lot more force working against the pistons and bottom end of a diesel as it is, without adding the turbo. So no your truck isn't "race" but your engine requires every bit of its strength to hold that compression inside and the resulting force of the power cycle. "built" doesnt have to mean race lol.
your guess on the injection pump is what I have basicly understood as well. But dodge/volkswagon and a few other company's used boost compensators on the same/similar pump. So I've been thinking of trying to find another pump with the compensator and see what can be done. I found a blow up diagram from nissan with both boost/altitude compensation built in. So makes me think maybe the newer td25 or td27 used a similar injection pump with the boost parts already installed. but if im remembering right its the pump head that's calibrated for the motors fuel requirements. so im pretty sure a 2.7 wouldn't work on a 2.5 without the metering recalibration. I just pulled all my old school books out and started reading again to refresh myself as I have been having issues with my truck and fueling.
I've been thinking about boost levels too. I'd probably stay like your suggestion. I was think 5-8psi max. just enough to recover any horse power im already loosing and maybe a touch more. Id rather no smoke and some boost then screwing with the fuel screw a bunch. To me reliability/longevity is most important.
also if you said u could only build 3 psi boost with the wastegate set correctly. maybe your turbo is too big? when I started doing boost figure calculations vs cfm flow. I found my 1.8l nissan gas turbo worked nicely according to some flow maps I found. I was actually quiet surprised how small a turbo this motor would require even to touch 150hp. which seems dreamy from a little bit of boost. I also did map figures for an sr20 nissan (2L gas) and the turbo was actually quiet large and it would seem the diesel would barily touch anything worth looking at on its effecientcy scale. I also was thinking about a toyota surf/helux turbo. as the 2.4l would have simiar needs for boost. I did abit of googling awhile back and found a newer nissan xtrail diesel had a nice diameter turbo with ball bearing turbo that would meet the right mapping for our older fuel systems.
remember newer diesels run higher boost and typically run direct injection so there air requirements are different. I have also though about a variable geometry turbo.... but they aren't so easy to just "find" here. lol
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dc1184
- Posts: 17
- Joined: 11 years ago
- Location: Costa Rica
and now, here are some pics of the damage:
I'm not sure, but I think the pre cumbustion chamber came loose and caused the excessive damage on the crown of the piston. It's one sorry looking piston and valve (both valves look like that).
I was having overheating issues prior to this incident, but i'm still not sure if it's from the turbo. I have an EGT pyrometer on order and will be installed when I have the engine back up and running, that way we can look at some real numbers.
I'm not sure, but I think the pre cumbustion chamber came loose and caused the excessive damage on the crown of the piston. It's one sorry looking piston and valve (both valves look like that).
I was having overheating issues prior to this incident, but i'm still not sure if it's from the turbo. I have an EGT pyrometer on order and will be installed when I have the engine back up and running, that way we can look at some real numbers.
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ehtrain
- Posts: 144
- Joined: 12 years ago
- Location: regina, sk
wow thats some impressive damage lol. I'm not sure how your prechamber would have come loose. majority of it doesnt sit in the cylinder and squished between the head and block. did one of your valve retainers come out? that happens if you really over rev a motor and get valve "float" or spin the motor beyond is valve opening ability. pushrods have a lot of slop in the valve train. which is usually why they have lower rpm limits unless its roller rocker arms.
hey the company that you got your cylinder head from able to speak english and order parts? thats a very hard to beat price for a new OEM cylinder head. best quote ive got for a blank new was 1200 +ship + duty. So I would gladly order a cylinder head from them for 550 lol.
hey the company that you got your cylinder head from able to speak english and order parts? thats a very hard to beat price for a new OEM cylinder head. best quote ive got for a blank new was 1200 +ship + duty. So I would gladly order a cylinder head from them for 550 lol.
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dc1184
- Posts: 17
- Joined: 11 years ago
- Location: Costa Rica
yeah, some serious damage there. I'm not sure if it was the valve coming loose or the prechamber. the "mechanic" who disassembled it didn't have much insight.
I do have the motor assembled and installed, I've been driving it easy the last couple of days. but, i have the same damn problem that you had with the head gasket. brand new (non-oem) head gasket, and there is visible weeping around the edges. Similar to your rebuild, I can see oil escaping onto the engine block. I now have the oem head gasket ($100 vs. $40 non-oem in these parts), and it's going to be installed tomorrow. what a pain in the butt having to change a brand new head gasket, hopefully the oem version seals better.
I have bubbles in the rad, bubbles in the overflow tank, it's running a little bit hotter than normal, and I'm losing a bit of water. I'm guessing these problems are all from the lousy head gasket. Any advice before putting on the new head gasket? we're going to verify the block and head (although it's brand new) to make sure they are flat within spec.
Regarding the new head I got here, it was $550 but it's completely blank. It does come with precombustion chambers installed however. I'm not sure if it's oem or not, but I can check. shipping is going to be hefty since it's not light. I'll grab one for you if you coordinate shipping. or, if you want you could certainly call the place directly on your own, but it's going to be spanish only i'm afraid. Just send me a message and I'll do what I can.
Cheers!
Dan C
I do have the motor assembled and installed, I've been driving it easy the last couple of days. but, i have the same damn problem that you had with the head gasket. brand new (non-oem) head gasket, and there is visible weeping around the edges. Similar to your rebuild, I can see oil escaping onto the engine block. I now have the oem head gasket ($100 vs. $40 non-oem in these parts), and it's going to be installed tomorrow. what a pain in the butt having to change a brand new head gasket, hopefully the oem version seals better.
I have bubbles in the rad, bubbles in the overflow tank, it's running a little bit hotter than normal, and I'm losing a bit of water. I'm guessing these problems are all from the lousy head gasket. Any advice before putting on the new head gasket? we're going to verify the block and head (although it's brand new) to make sure they are flat within spec.
Regarding the new head I got here, it was $550 but it's completely blank. It does come with precombustion chambers installed however. I'm not sure if it's oem or not, but I can check. shipping is going to be hefty since it's not light. I'll grab one for you if you coordinate shipping. or, if you want you could certainly call the place directly on your own, but it's going to be spanish only i'm afraid. Just send me a message and I'll do what I can.
Cheers!
Dan C
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ehtrain
- Posts: 144
- Joined: 12 years ago
- Location: regina, sk
ok I will keep you updated on the cylinder head.
Thats REALLY sucks about the head gasket. I know I was really pissed off lol. OEM seems to be holding up perfect though.
when I put the OEM gasket in I paid very close attention to all the o-rings. The oem gasket seemed to bond the o-ring to the metal somehow, where as the aftermarket didnt look as quality. So my guess was as head clamped down it twisted the o-rings causing a leak.
if your tearing down again. just make sure your following the 2 or 3 step rule when tightening head bolts in the proper sequence. slow and even is better then spec torque right off the hop. Also even though its a new head did anyone crack/pressure check it? I'd hope its all good but you never know. someone could have dropped it in shipping or who knows.
bubbles in the rad and burning oil usually indicates a bad head gasket or a cracked head and oil leak. but if your seeing seeping like I was on the outside and your boosted. that would add some extra variables lol.
Thats REALLY sucks about the head gasket. I know I was really pissed off lol. OEM seems to be holding up perfect though.
when I put the OEM gasket in I paid very close attention to all the o-rings. The oem gasket seemed to bond the o-ring to the metal somehow, where as the aftermarket didnt look as quality. So my guess was as head clamped down it twisted the o-rings causing a leak.
if your tearing down again. just make sure your following the 2 or 3 step rule when tightening head bolts in the proper sequence. slow and even is better then spec torque right off the hop. Also even though its a new head did anyone crack/pressure check it? I'd hope its all good but you never know. someone could have dropped it in shipping or who knows.
bubbles in the rad and burning oil usually indicates a bad head gasket or a cracked head and oil leak. but if your seeing seeping like I was on the outside and your boosted. that would add some extra variables lol.
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dc1184
- Posts: 17
- Joined: 11 years ago
- Location: Costa Rica
ok, thanks for the heads up. i'll be interested to see what the current head gasket looks like when we get the head off tomorrow. I'm expecting to see a noticeable leak somewhere obvious.
also, i forgot to mention that I am running without the turbo installed right now. i want to get everything running just right sans turbo, that way I can eliminate variables that the turbo brings into the picture.
also, i forgot to mention that I am running without the turbo installed right now. i want to get everything running just right sans turbo, that way I can eliminate variables that the turbo brings into the picture.
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elboss
- Posts: 59
- Joined: 12 years ago
- Location: Portugal
From My experience, i bet, your problem, is RPMS to much high! Like over reving to much time i think, or a "old" problem from the engine before you have it....
My sd 22 is running on 22 Psi, and i dont have problems until iet, and my Opel corsa 1700cc Turbo diesel (isuzo engine) still running 21 psi, with 37.282 milles still runing
My sd 22 is running on 22 Psi, and i dont have problems until iet, and my Opel corsa 1700cc Turbo diesel (isuzo engine) still running 21 psi, with 37.282 milles still runing
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