1986 930 w SC cams valve - piston clearance

[flatsix965]

Hi,
Just joined the forum today looking for some help
I am rebuilding my 1986 930 engine using Wayne's book. I decided to install SC cams on it as I understood from several threads that there should not be any issues with it. While I was doing the valve to piston clearance check recommended in the manual I noticed that the clearance on the intake valve#1 was marginal (close but not quite the recommended 1.5 mm). I decided to check the other 5 intake valves and I found the same results. The closest point is after TDC when the valve is fully open. Checked all the exhaust valves and are ok (above 2mm). The SC cams is the only modification on my engine and it has not been machined so I wonder why I am having this clearance issue. Both cams were timed close to 1.55mm with .1mm valve clearance. Has anybody experienced the same? What intake valve clearance values should I expect with the SC cams on a stock 3.3 engine? Any recommendations? Thanks!!!

[jwasbury]

Originally Posted by flatsix965

The SC cams is the only modification on my engine and it has not been machined

Have you owned the car since new? Are you certain that the engine has never been apart before? Maybe a PO had machine work done...you never really know unless you bought new.

When I tore down my engine, I found numbers scribed on the underside of the pistons...surprise! The engine was apart before. I spoke with most of the POs of my car, including the guy who owned the longest (for 20 years or so starting 1981). None of them remembered doing any major work on the car.

Just a thought.

[voitureltd]

When I tore down my engine, I found numbers scribed on the underside of the pistons...surprise! The engine was apart before. I spoke with most of the POs of my car, including the guy who owned the longest (for 20 years or so starting 1981). None of them remembered doing any major work on the car.

Just a thought.[/QUOTE]

Previous owner may have played with the boost or ??? also may have been Euro with bad EPA stuff added to pass when brought in. Is your car Euro? Judging by the parts replaced when you were in there what do you think was the causal part and what caused it to fail? A little off topic, Sorry

[TurboKraft]

Originally Posted by flatsix965

The closest point is after TDC when the valve is fully open. Checked all the exhaust valves and are ok (above 2mm). The SC cams is the only modification on my engine and it has not been machined so I wonder why I am having this clearance issue. Both cams were timed close to 1.55mm with .1mm valve clearance.

Are you saying you set the piston to TDC and set the valve at full open, too?
If so, that's not a scenario that's going to happen when running.

Set the piston to TDC.
Adjust the valve lash.
Time the camshaft to the spec you want, lock it down.

Now carefully loosen the valve adjuster locknut. Since the adjuster has 1.0mm threads, 1.5 turns is 1.5mm distance. You should be able to rotate the adjuster bolt (elephant foot) 1.5x and still not have the valve contact the piston.

Even if you set the cams at full advance, you should have plenty of piston-to-valve clearance.

If it contacts, have valve reliefs machined into the pistons.

[flatsix965]

Originally Posted by TurboKraft

Are you saying you set the piston to TDC and set the valve at full open, too?
If so, that's not a scenario that's going to happen when running.

Set the piston to TDC.
Adjust the valve lash.
Time the camshaft to the spec you want, lock it down.

Now carefully loosen the valve adjuster locknut. Since the adjuster has 1.0mm threads, 1.5 turns is 1.5mm distance. You should be able to rotate the adjuster bolt (elephant foot) 1.5x and still not have the valve contact the piston.

Even if you set the cams at full advance, you should have plenty of piston-to-valve clearance.

If it contacts, have valve reliefs machined into the pistons.

Chris,
I guess I did not explain it clearly. The procedure in Wayne's book ask to measure the valve to piston clearance when the valve starts to open and continue every 10 deg until it is fully open. What I was trying to describe is that in my case the smallest clearance occurs at the end of this process when the valve is fully open which is after TDC and the piston is moving towards the crankshaft. Any idea what the smallest values (above 1.5mm) should be for my combination (930 cams regrinded to SC profile on stock engine)? Thanks!!

[flatsix965]

To conclude this post. Clearance was not the problem it was coil bind, or the valve spring retainer hitting the seal. Thanks to John Doudherty for the advise.