looking for valve/piston clearance solution
 

Clearance is good on #1 intake and exhaust and on #4 exhaust, but #4 intake is only about 1.2mm at the highest point on the lobe, estimated by turns of the valve adjuster screw.

1983 3.0
heads were resurfaced (for the first time)
964 cam grind
1 copper gasket at cylinder (.25)
timing set to 1.7 mm

I did some reading of other threads but am not sure what the best course of action is. Should I add another .25 gasket? Should I bring the timing back to 1.5 or so and re-check? If the later, can I do this with the hydraulic tensioners installed?

Clearence should't wary between #1 intake and #4 intake, assuming all heads was cut the equally. Recheck camshaft timing between left and right bank.

Have you checket piston to valve clearence over a wider range, not only at max lift?

Yes, I checked clearance over a range, per instructions in Wayne's book. I really meant when the piston is closest to the valve rather than max lift. If I have to reset the timing, can I do it with the tensioners intact, or should I remove them and hold the chain tight with a clamp as when I initially set it up?

Baby

If your tensioner is already decompressed and extended tightly, you can do the valve timing with them. You may prefer to use a clamp or something similar to keep the chain tight but you do not need to remove the tensioners.

Great, thanks!

I had similar intake clearance issues after rebuilt heads with new valve seats. I got a number of responses here suggesting 1.0mm is OK, I ran it with 1.25mm clearance (including track - hot & bouncing off rev limiter on occasion) and had no issues with clearance. Unfortunately I did eventually have issues with exhaust valve guides, but that's a different story.

http://forums.pelicanparts.com/911-engine-rebuilding-forum/694888-valve-piston-clearance-stock-3-2-engine.html

If you think about it, the intake valve won't hit the piston if it should float, as it's closest when it is opening. The exhaust valve is the one that would hit the piston if it floats, because it's closing when it is closest.

If clearances are close like this, I think you should check the other cylinders also just to make sure there isn't a really super tight one in there. There is going to be some variation - I had a range of 0.4 mm. So if randomly the larger clearance valves had been at the #1 & #4 location instead of the tighter ones, I'd never have been the wiser ...

As Bergermeister says, you don't have a problem. The min according to the factory manual is .8mm.

-Andy

Well, I am always happy to hear I don't have a problem! Burgermeister, I had read your thread earlier but wondered if possibly a 3.0 with the 964 grind might not present other issues or if the minimum measurement might actually be different.

If the factory manual says .8mm, why does Wayne's book advise 1.5mm? Padding for novices with toy tools?


I checked my timing carefully a few times per side once I had torqued the cam shaft bolts. I'll check it again and check the clearances across all the cylinders. I still don't quite understand everything that affects the clearance e.g., new valve seats, but thanks to you guys I'm learning.

I'm also running closer to 1 than 1.5 mm, don't remember how close. I'm regularly bouncing the stop at 6800.

You have clearance, Clarence...
https://www.youtube.com/watch?v=MQ9iPTu_FMA

Well, that puts it all in perspective...

Issue resolved. The timing on the passenger-side was off a few mm, compared to the driver side. Strange, as I checked it like four times after I torqued down the bolt. I adjusted it---basically moved the pin to the next hole. Now it matches the driver side, and there's all kinds of clearance, Clarence. Thanks again, everybody. It's hard to believe the end is in sight.

Not trying to be a jerk by mentioning this. Just curious why your cam timing lift spec. at TDC overlap is 1.7mm The common spec for 964 cam is 1.26mm

KTL, the gent who ground the cams recommended 1.7-1.8 mm. I guess the theory is you get back the bit of torque you lose with the 964. I'm always open to suggestions, so please don't worry about offending me. It's almost impossible.

Well reason I asked was because of what I experienced with some reground cams on my '87. They were stock cams ground to a DC-20 "Super C2" 964 modified profile. Recommended lift spec at TDC overlap for those is 2.2-2.4mm.

I have stock pistons and first time cut heads too. When checking P-V clearance, I couldn't get the recommended exhaust valve clearance. I ended up reducing the lift spec to 1.85mm? But keep in mind that I was going with the conservative rule of thumb for 2.0mm on exhaust clearance. I could have been closer to the recommended lift spec had I gone with a less conservative P-V clearance.

I have the 993SS grind in my 3.2 timed at 1.8 mm. It really didn't do anything good with my engine, when I get time I'll retime them to 1.2-1.3 mm.
If that sucks jast as much, I'll go back to the stock cams.

Not sure if 993SS is the same as DC20 or what.

Valve clearance
 

I have a similar problem with my 73 E. I made no performance changes, simply a boring stock rebuild. I was not even going to check the clearance but decided why not.
I checked #1 intake and exhaust as well as #4 exhaust and found not problem. Then on #4 intake I get approx. .75 mm. I can't figure whats up. I am positive(almost) that the pistons are in the proper position. The rocker on the shaft was a bit stiff but I rotated it 180 degrees and have fluid movement. The shaft was difficult to get into the cam housing bore but seems to move freely.
At this time i am going to remove the rocker shaft and recheck everything associated with it. BTW the cam timing is set at 2.90 side to side - however I get a difference of approx .04 mm sometimes as I check it again and again.
Any suggestions?
Thanks,
Bill

Bill - read the 2.7 cam discussion going on for a theory on why the timing can move around a little bit (and 0.04mm is a very little bit) normally.

When I find a tight rocker I also find I goofed up installing the shaft. If it is in wrong and tightened, that can nearly lock the rocker. Though usually when I make this mistake it is on a whole row of shafts. Or did you rotate your shaft 180 degrees and found things freer?

valve to piston clearance
 

I rotated the rocker on the shaft 180 degrees and found it not to bind. That is the way I installed it in the engine. It was also quite a tight fit having to be tapped in gently through the rocker and into the outer bore. I believe I need to remove the shaft and install a different one (for test purposes only) to see if indeed the shaft is binding. Any suggestions on removing the tight rocker shaft. It cannot be pushed out with my fingers and there is only so much room to tap or force it out from the cam box side of the engine. I also need to add that at the point the rocker gets tight (approx one turn), the crankshaft rotation gets tight to the point I do not want to force it.
It would seem to me if the rocker was binding the turning of the crank shaft would overcome the tightness. Before I installed the rocker I could rotate it on the shaft with only a tight area not a total bind.
Thanks for any help or suggestions.
Bill

Bill

Tight fit is good for rocker shafts in the housing - means possibility of less weaping of oil, and that the forces start being taken up by the housing right at the inner edge, and not back by where you expand the ends. Though some are a finger push through sometimes, and can work just fine.

But a rocker itself should not bind at all anywhere in its travel. With the adjuster screwed all the way up, you should be able to move the rocker with the cam on the base circle through all its travel without feeling anything at all. Rockers usually have a fair amount of side to side end play, so they ought not to bind against the sides of the housing. I suppose if a bushing is a bit long, that could happen (and be easy to fix). Short of some kind of damage in handling (maybe a gouge from tools used to push shafts out?), with the rockers out of the car the shafts should just drop through. If they don't, one guess would be that a rebushed rocker didn't get honed to the right ID?

You need to use ingenuity to get the rocker shafts out of an assembled motor without much disassembly (as in, it is in the car). But it can be done. You can put sockets in which are a bit smaller than the shaft OD, and pry against them. As the shaft moves in some, you use longer ones, or add a second, etc. You have to watch out for prying too hard using magnesium chain housings for the ones at the back of the motor, and there are problems with the sheet metal at the other end, so about a third of the shafts can be a bit of a bear.

With hardware removed, it is possible to run a long thin bolt through a shaft whose other end is hard to access (but you have to have some), and with suitable washers or similar things on it, use it and prying to pull a shaft rather than push.