SD25 Turbo Blues

SD diesels were widely available in the US in the 1981-86 Datsun/Nissan 720 pickups, and in Canada through '87 in the D21 pickup.

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asavage
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#31

Post by asavage »

dc1184 wrote:Hey Al, thanks for the info. I guess I have nothing to lose by trying one of those fix-in-a-bottle solutions.
Now that I've gone and read more of this thread, I know you've just had it apart, and it's not going to be a problem that can be remedied by snake oil. This is either a wear or mismatched parts issue.

These pictures:
Image] Image

There's only one way a valve gets like that, and it's because it hit something. Normally, I'd say it stuck open (siezed in its guide). However,

a) The piston has damage in more than just the area where the valve hit;
b) The piston didn't come loose of its gudgeon pin.

The cracked piston skirt etc. can be caused by the valve striking the piston, but how did the rest of the piston crown become so beat up? Heat could have seized the valve in its guide, or the retainer (disk-shaped) may have failed and allowed the valve to "fall down" into the cylinder but I assume they'd have told you about a failed retainer. That piston crown looks suspicious.

There's a mystery here. Did some foreign object make it down the intake tract?

Are we sure both that piston and valve came from your engine, and from the same cylinder?

Leaving that all aside, you are probably running very short gearing for the SD25, and I can tell you from experience that the SD does not take well to being run up at the governor cutout for long. You may want to invest in a cheap TinyTach ($50, last time I looked) for your dash.
It's a bummer, because in January I had the whole engine apart (after cracking a piston). it's got a new piston, I was told the other 3 were fine, and new rings on all 4 pistons (hasting). The bores were checked by a third-world machine shop, and checked out fine according to them. Plus the head is brand new with two brand new valves. The new head was blank, so the rest of the assembly came from the old head.

I was expecting much higher compression readings myself. Maybe, for some reason, the rings didn't seat correctly.
You'd know about that, as the blowby (vapor coming out of the valve cover if you remove the oil fill cap while idling) would be as bad as a used engine. Having said that, I'm not a fan of re-ringing diesels: bores wear oval-shaped and tapered. The taper is not a problem, but trying to wear a new round ring into an oval bore is nearly impossible, leading to extremely long break-in times.

The early SDs used draft tubes; your later one has the sealed system -- it has the crankcase breather routed to the intake. It's partly for emissions (those road draft tubes released a lot of hydrocarbons) and partly to keep dirt out of the inside of the engine.

Does your SD25 have EGR?
Elboss, sorry but I don't know the part number for the VE pump. I can send you the numbers off the housing of my SD25 VE pump if you'd like.
That would be good to have posted, for future reference.
I don't think the SD25 VE pump works on the SD22 though.
The Inline IP uses a four-bolt, rectangular mounting.
The Distributor IP uses a three-bolt, triangular mounting.

So, you'd have to modify the mounting plate or get one from a matching engine.

EGT should not run over 1150°F continuously for reliable operation. I think we have a link somewhere to Banks' website where they put out that number.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.
plenzen
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#32

Post by plenzen »

Pump number recorded by rebuild shop where i just had it done is

Zex104740-4790
Ser# 16700-4790

HTH
Retired Pauly
Problem with being retired is that you never get a day off.
1987 D21-J SD25 KC
KJLGD21FN
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asavage
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#33

Post by asavage »

Yeah, but that's not all the numbers related to the IP. There are more there.
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asavage
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#34

Post by asavage »

I hate to suggest it, but . . . wrong head gasket?

Wrong head gasket (too thick) would reduce your compression. On a diesel, a few thousandths can make a large difference.
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dc1184
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#35

Post by dc1184 »

well, the more I think about this, the more suspicious I become. Am I sure that the valve and piston came out of my engine? That's probably the best question to ask here, and my answer would be "no". I was not present when the engine was disassembled.

Fraud is rampant here, especially among "mechanics". These engines are quite common here too, so it would be very easy to hand me a banged up SD25 piston and valve that were sitting around the shop and say "here's your piston, and valve, you'll pay me $xxxx to rebuild the engine, right?"

I bet that is what happened. Lucky for me, I smelled something fishy at the time, and had the engine rebuilt elsewhere. wouldn't it be surprising that the bore that the damaged piston came from didn't show much damage at all?

I am positive that the headgasket is the right one, I purchased it. I first used an aftermarket headgasket that was stamped for "SD23/25", but it leaked a bit. I then went to the nissan dealer and bought an OEM headgasket, some copper gasket sealant, and it hasn't leaked a bit. I'm confident about the headgasket, much less confident about the integrity of the local mechanics.

I am running short gearing, and she does runs at high rpms frequently. a tach and an overdrive are both in order. I try to be very cognizant not to push her at max rpms for extended periods of time though. usually it's only climbing a big hill on the freeway. the turbo allows me to back off the throttle a bit.
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asavage
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#36

Post by asavage »

dc1184 wrote:wouldn't it be surprising that the bore that the damaged piston came from didn't show much damage at all?
You might be surprised. I"ve seen a piston with a hole in it (old VWs were famous for that) with a quite decent bore.
I am positive that the headgasket is the right one, I purchased it.
As you re-used three of your pistons, I'm out of guesses at to the reason for the low compression. I suppose you could second-guess the compression tester.

As you're not really experiencing problems, maybe this is something you should just [shrug] at. That is, if it starts OK, doesn't use oil and doesn't belch blue-ish smoke, it's not broken.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.
ehtrain
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#37

Post by ehtrain »

my injection pump numbers are
16700 14G03
104740-4790

i have another ve pump body ill dig out when i remember and see what those numbers are for refference also
ehtrain
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#38

Post by ehtrain »

did you get your truck running good? are you still able to get rotary injection pumps? i may need some other parts for my next project
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