lifter preload

[rv8500]

Hi, can anyone help me? I am a new owner of a 5ltr chimaera with a few problems. What should the preload be set too? Is it .020" - .060" as in a normal rover v8. Mine appears to be .100" (must be too much) Also my car is a 97 but my cylinder heads and rockers are all dated 94, is this normal or has my car its heads changed? Thanks

[boosted ls1]

It's still a rover engine so I'd stick to the measurements you have. You can measure it with a paperclip after the clip has been checked with a micrometer. I don't knoiw if tvr have there own clearance but doubt it. Have you had the heads skimmed or got tin gaskets fitted?

[rv8500]

I havn't had the heads skimmed, but they might have been done before I bought it. The engine has been to bits before, because the inlet gasket was covered in black sealer and that can't be original I'm using a composit gasket from tvr gear. The cars only done 18500 miles so it can't be too bad! (I hope) Thanks

[boosted ls1]

The .100" clearance you have will make the valves lift less. Composite gaskets are usually around .040" thick. Tin gaskets are usually .025" and will raise your c/r a smidgen. You may be able to measure the thickness you have with feeler guages inserted in between the head and block. The new gasket may be thicker then the old if it's a different type. If your engine isn't rattling you could leave as is or rectify it. Rectification is usually via adjustable rocker arms or adjustable pushrods. I'd guess that you have adjustable arms. You could have the rocker posts milled shorter or remove any shims underneath them to restore a more acceptable clearance. Don't forget that if you do this you have to be aware of the rocker arm ratio which is 1.6 for a stock arm IIRC. So a small shil under the pedestal has a greater effect at the lifter.

[rv8500]

Oh no, thanks for the reply but I thought the bigger the shim under the rocker pedestal the less the preload. I've taken the cylinder head off the drivers side today and valves 4 and 6 havn't been closing properly, I'm guessing this is my problem. If the heads dated 94 it must have been changed at some time, so could be a miss-match of bits.

[boosted ls1]

If you examine the heads there will be a date in the casting. I think you will find it by one of the exhaust ports. It will be a circle with the year in the middle. Both your heads should be the same and hopefully to the exact same spec. How do you know those valves aren't closing if you don't mind my asking. Have you got a stock head on one bank? Mike.

[rv8500]

Yep, the date on the heads (both of them) is 94, also on the rockers. They are tvr spec with 42.8mm inlets and really well ported and polished. The exhaust valves on 4 and 6 have black soot on the seating face ( I had low compresion on those two cylinders only when warm) The bores look imaculate tho.

[HarryW]

rv8500 said:

Yep, the date on the heads (both of them) is 94, also on the rockers. They are tvr spec with 42.8mm inlets and really well ported and polished. The exhaust valves on 4 and 6 have black soot on the seating face ( I had low compresion on those two cylinders only when warm) The bores look imaculate tho.

Not sure what the standard valve size is on the 500 but at 42.8mm that equates to 1.67" in old money which is BV country, if its fully ported then they could be stage IV after-market heads, which could help explain the year stamp.
I'm sure there are more knowledgeable people on here with 500's who could clear that point up .
Out of interest, what compression figures did you get to make you take it all apart . Did you do just static compressions or a set of dynamic ones as well, if so, if you don't mind me asking what figures did you get .

Harry

[rv8500]

I just did a static compression test with a not very good tester, but when it was hot I got 15 psi The good valves were reading about 125 psi, which isnt great either but my guage might not be too acurate. The car did run well tho, just had a bit rough idle and a miss fire upto 2000 rpm then was fine. I'm sure its had work done but not had its pre load set holding these two valves slightly open (they gave a good seal when the rockers were removed) so it cant have run properly for a long time.