3.2 - Clearance piston/valve too tight - right side only

[cpetommy]

I'm in the process of re-building a '87 3.2 motor and in the process of checking the piston to valve clearance, the right side, cylinder # 4 , the intake clearance is only about 0.31 mm while the left side is an acceptable 1.5 mm (#1). This is a stock re-build with the exception of using DC-19 cams which were re-checked by John Dougherty. The lift at overlap is 1.93mm (John specs 1.8 - 2.0mm). The only machining done was R&R of the valve guides, re-bushing the connecting rods and rocker arms and re-facing the rocker arms. All (new) journal bearings were std. I've re-checked this several times and at a lost as to why this is happening

Appreciate any suggestions

[Eagledriver]

I don't know why the reading would be different side to side. Maybe the valve is seated deeper on the number 1 head than the number 4 head. Maybe more material was taken off the face of the heads on the right side. The cam is going to run closer than a stock cam would. You can either shim the cylinders, retard the cam timing, or have pockets cut in the pistons, or do a combination of these. If you want to cut the pistons, Ted Robinson at German Precision can do it.

-Andy

[KTL]

I had a problem with setting my lift @ TDC overlap with DC20 cams. Spec for DC20 is 2.2-2.4mm. I had to back mine down to 1.85mm because I couldn't get adequate piston-to-valve clearance at lift any more than that.

That's a substantial difference from side to side. Have you tried checking the intake P-V clearance on another cylinder on that same side? How does the exhaust clearance check on that same cylinder?

[cpetommy]

Kevin, Andy

Thanks for your advice, I will check the clearance on all the intakes and exhaust on the right side. Ted Robinson performed all the cleaning and machining on this engine so I know no anomalies were noted by Ted. The only difference that he did noticed was that one of the cam carriers had a 964 prefix in it's part number but since Ted didn't mention anything about it I figured they are interchangeable. If it turns out that every right side clearance is "tight" then my next step is to haul the motor off to Ted to confirm the clearance problem and have him machine the pockets into the pistons but it sure sounds strange to only have to do one side - I keep thinking that maybe I'm doing something wrong.

Tommy

[Aurel]

Maybe you had different chain tensions on both sides when you set the timing. That would cause timing values to differ once the tensionners reinstalled, resulting in different valve-piston clearance values. Did you make sure that the overlap at TDC was identical on both sides after reinstalling the tensioners?

Aurel

[cpetommy]

Aurel,
The lift at overlap were not exactly the same at TDC but they were in spec. You bring up a good point however, I didn't have the right tool to really put a strong tension on the right side chain. I 'm considering buying the fixed chain tensioners that Wayne sells and I'm also considering the purchase of the TDC indicating tool to verify the Z1 mark on my new pulley.

Tommy

[racing97]

The TDC mark is a good point to check any time you replace cams.

regards

[KTL]

TDC is the standard location to set the lift spec. But it is not always the point at which you will find minimum P-V clearance for any given cam. For instance, with my DC20 cams, I found the min. P-V clearance to be well past Z1/TDC overlap mark on the pulley. My min. P-V was found to be approx. 10 degrees past TDC overlap.

[Aurel]

Correct. The easiest way I found to check the PV clearance was to set the valve to the minimum clearance value with the adjustment screw, then rotate the crankshaft over the entire cycle to make sure the valve and piston never touch. Needless to say not to force if any resistance is encontered...

Aurel

[racing97]

Check for the TDC mark to be correct on the pulley by measursing psiton position and using a degree wheel and a dial indicator or a positive piston stop in the chamber rotate in both directions until you are against the stop both ways check and split your readings on the crank degree wheel. Rarely is this off and in your lifetime you may only see one but when it is it will cause a poor runing motor.

regards

[304065]

Pistons in upside down?

Right case half spigots decked at a prior rebuild due to broken headstud on one?

Are cylinder heights the same left to right?

964 cam carrier? Which side is it on? I would be extremely suspect of anything with a 964 part number where a 901 should be.