VALVE CLEARANCE AND PRELOAD PROBLEM

[gulf blue rsr]

Hi,

I'm building a 3.5 with Viper Typhoon cam and stage 2 heads.

I bought the block with the cam in and used for about 5,000 miles so the lifters (standard) are already pumped up, they have sat in my garage for a few months waiting for me to find the time to get on with the job and here I am!

Last night I did a trial test run to see if the valves are going to clear the pistons, I'm going to be using composite gaskets, rather than damage the new gaskets I decided to try with an old tin one using the theory that if they clear with the tin then I'm definitely safe with the composite!

1st I tried with no shims in the rocker gear and the valves "just" touched the piston, squashing the plasticine out and leaving the tiniest mark on the pistons, then I tried with the composite gasket and a shim, sorry forgot to check the thickness! but I then had plenty of clearance.

The thing I then thought of was, assuming the engine has been run and the lifters pumped up, would they have bled down whilst standing for months or would they have stayed fully pumped up and so I have now tested with the maximum lift? I know I have to strip and empty them to set the preload, I guess what I'm really asking is if I empty them and try again, what is the difference in lift between empty and pumped up? how can I set them at the highest lift to check valve/piston clearance?

sorry for the long post but bit difficult to explain!!

Thanks STEVE

[ChrisJC]

In my experience, lifters will stay pumped up, and the only way to get them to go down is to remove them, strip them down & remove the oil, reassemble and put back in.....

Others may have a different opinion.

Chris.

[sidecar]

I think that you need to set the engine up for the "worst case" in otherwords you need to check the clearance before, at , and after TDC with the lifter fully pumped up with something solid.

When I built my engine I used an OLD lifter that I heated up then filled with candle wax. Whilst it was still hot I fitted the inner cup an spring clip, I then poured in a bit more wax that run down the sides of the inner cup. Once the whole thing has cooled down clean off the excess wax from the inner cup and tested that inner cup can not be pressed down at all. Using a couple of followers that have been locked up solid will ensure that the measurements that you are taking are accurate and are "worse case".

It sounds to me that you setup is a bit marginal, I though that the cleanance needed to be in the order of at least a couple of mm.

A clever chap on this forum made a fly cutter out of some old chevy valves, it might be an idea to find out a bit more about them.

Oh by the way, if you cut in half an old rocker shaft spacer spring it makes two really good light weight tester springs that you can use for the valves. Using them means that you can set the engine up say 40 degrees BTDC then just push the valve by hand to see how much clearance there is. You can put a DTI on the end if you like. You can then turn the engine 10 degrees and repeat the test, do this until 40 degrees ATDC.

Personally I would not use shims to set the preload, I found them to be a total pain in the ass! I'd go for RS adjustable pushrods and set the pre load to 20 thou. You could use two tin gaskets on one head to simulate one comp gasket.

HTH,

Pete

[HairbearTE]

I stripped down a 3.5 last monday that, judging by the smell of it hadn't been opened up for a very long time (I've had it over 10 years and never touched it). It was a p5/p6 engine and may not have ran for 20+ years. Almost all the lifters were pumped still, only 2 or 3 had bled down. There was a guy who used to sell useful little tools for working on RV8's on ebay. He used to sell lifters that been made solid by whatever means for people to use for checking valve clearance etc., he used to sell 'em for around £4 a pop iirc.

[450 racein]

Hi,pre/load aside, your valve to piston clearance hear sounds like an isue, you are going to have to make sure it ok , if not it's cut out's in pistons. has this motor run prior to this stopage ok? . DB p/s If you are not sure check your valve train tollerances all the way through .