SD22 cam profile

[philip]

For those of you familiar with cam profiles in gasoline engines, take a look at this cam profile (taken from the FSM) of the naturally aspirated SD diesels!

Camshaft Calculations - Lobe Center / Duration
The SD22 has an Overlap of 56.00 degrees and has in Intake Duration of 275.00 degrees. The Exhaust Duration is 275.00 degrees. The Inlet Cam has an Installed Centerline of 109.50 degrees ATDC. The exhaust cam has an Installed Centerline of 109.50 degrees BTDC.

[philip]

>Any idea what the valve lift on the SD22 is? I can't find it, nor can I deduce it from the specs that I have, but if my measurement of the wear on the valve stem is correct it's about .325". <

Galen. I looked high and low ... didn't find the actual advertised lift nor the base circle dimension in the FSM. But the dimension from the top of the cam lobe to the heel is provided. So ... all you need do is measure 90 degrees (across the cam) to get the base circle dimension and then subtract the difference to get lobe lift AND ... multiply by 1.5:1 which is the rocker arm ratio to get valve lift. The SD cam is not so 'wild' that you could not do this.

I notice the regrind has virtually the same lobe centers (110 vs. 109°) and the overlap had been reduced CONSIDERABLY. Considering the SD's low rpm operating RPM, the large amount of valve overlap can only be there for supplying more exhaust gas recirculation than the EGR valve by itself could provide. The high amount of base injection timing (20°) speaks to all this "built-in" EGR from valve overlap. The reduction in overlap induced EGR may well affect how much base injection timing the engine wants.

[Knucklehead]

The problem with that, if I understand you correctly, is that the base circle dimension of my cam is no longer the same. I should have measured it before I sent it out, but didn't realize the stock lift was unpublished. I'll check with the grinder. I'm going to check piston/valve clearance anyway. And get new springs. They're all about .1" low.

[philip]

The problem with that, if I understand you correctly, is that the base circle dimension of my cam is no longer the same. I should have measured it before I sent it out, but didn't realize the stock lift was unpublished. I'll check with the grinder. I'm going to check piston/valve clearance anyway. And get new springs. They're all about .1" low.

This is one of the "problems" (depending) with reground cams. The base circle is reduced with as little as possible metal removal from the lobe in order to get more lift. This can raise hell with flat tappet wear rates and if the profile gains more effective lift, then valve float is encouraged. But with the SD, RPM seldom reaches 4,000 rpm. Regrounds are a great / economical way to try out various cam profiles without spending a lot of money. But they are not a long term thing in many cases.

Anyway, you can still measure the total cam lobe height minus the cross measurement (90 degrees to lobe height) and subtract the difference... times the 1.5 rocker arm ratio to get valve lift. Yeah, I would still clay check the installed valve lift because afterall, these pistons have little in the way of protective valve pockets.

[philip]

SNIP I'm going to check piston/valve clearance anyway. SNIP

In these photos, Galen depicts one combustion chamber with modeling clay on the valve heads. The idea is to partially assemble the engine, install the cylinder head and valve gear. Then, turn the crankshaft from about 30 degrees BTDC through TDC to about 30 degrees ATDC (overlap: end of exhaust, beginning of intake stroke). The clay deforms leaving an impression of minimum piston/valve clearances.

[philip]

The problem with that, if I understand you correctly, is that the base circle dimension of my cam is no longer the same. I should have measured it before I sent it out, but didn't realize the stock lift was unpublished. I'll check with the grinder. I'm going to check piston/valve clearance anyway. And get new springs. They're all about .1" low.

I stumbled across this "advisory" on the Crower Cam website :

Camshaft Hardfacing and Regrinds

Crower is always introducing new cam cores to the market. In the pipeline are plans for BMW S14 (4 cyl) and S50 (6 cyl) DOHC cam cores. But until there's a core offered for your particular engine make...you'll have to settle for a regrind or hardface. When you supply Crower your stock cam core, we draw on 50 years of camshaft experience to grind the exact profile required for your particular application. Whether it's street, street/strip, road rally race or full blown drag, Crower has the profile you need. You supply factory core(s). Specify street (stage 1), street/strip (stage 2), race (stage 3).

Two options:
1. Hardfacing - This is a race application, limited street. Welding up stock lobes to allow unlimited spec while maintaining stock base circle. Cost is $40 per lobe (8 lobes = $320 total) plus $100 per cam for the grinding. You supply stock cores. No wear or compatibility issues.

2. Straight regrind- Reduced base circle allows more lobe lift. Limited spec, emphasis on top end power. Typical specs are .005" to .010" more lift, 5 to 10 degrees more duration at .050" and about 5-10 more hp depending on engine mods. $134.50 per cam for the grinding. You supply stock cores.