View Full Version : Lifter Pre-Load

03-07-04, 12:45 PM
I have a 3.9L RV8 in a GD that has done several thousand miles, but I am still not convinced that lifter pre-load has been set correctly during assembly. A rolling road session shows only 195 bhp at 5500 rpm at the flywheel, and 218 lb-ft at 3500 rpm. The car runs OKish - but nothing special, and is difficult to get within the legal 1200ppm hydrocarbon emissions at idle speed and 3.5% CO for the MOT. Idle is not smooth, and engine hunts a little.

The 3.9L block from RPi was built up with: Stage 2 heads; Piper HR 270 cam; Offenhauser-JWR inlet manifold; Weber 500 carb (jetted by RPi); Mallory dual-point dizzy set to 33 degs dwell; Cloyes duplex timing chain; NGK BP6ES plugs; a compression ratio of 9.75:1; timing set to 6degs btdc; and runs on 95 octane unleaded. A measure of compression showed all cylinders in range 9.8 to 10.4 bar, except one at 11.2 bar

I read that poorly set lifter pre-load can be a source of engine under-performance. Do you experts out there agree? If so, can it be easily reset on a fully assembled engine, or should I be looking at other causes for my disappointing engine performance?


03-07-04, 01:00 PM
Hi Rusty, with that cam in your tick over should be smooth as it is a bit tame. It is passable to check your pre-load on the hydraulic lifters but you will have to get all the oil out of them first as you can only do a preload check if they are empty. I would make sure that your cam is timed correctly as well as this will have a big effect on power verses torque. I also have a RV8 which I completely built myself and when I took it to a rolling road got a max power of 275bhp ( which I think is a bit high ) at the flywheel. Only real difference between our engines is I have a Piper 285 cam and stage 3 heads.


03-07-04, 03:29 PM
Hi Martin
Thanks for swift response! I guess I am going to have to get the heads off and double check the pre-load and cam timing even though I do believe they were set correctly when I built the engine - I am no expert but I did read relevant articles on how to do them correctly.
Incidently, can you recommend a good RV8 engine builder in our region if I get stuck, and is there a good rolling road place locally?
Many thanks

03-07-04, 03:41 PM
Hi Rusty, you don't actually have to take the heads off to do either, As for the cam timing, using a dial Gage through No1 cylinder spark plug hole get the engine to TDC making sure that you are on the correct stroke and then if you look at No 6 cylinder the valves should be in exactly the middle of swapping from closing the exhaust and opening the inlet valves. This means that both hydraulic lifters will have moved slightly by exactly the same amount. Not sure how to empty the hydraulic lifters but if you can operate them a few times with the engine off this might pump enough fluid out to check them. Again you need the heads on for this.

Afraid I am not too sure of many engine builders near you but one good one is Racemetal in Gainsborough.


03-07-04, 06:34 PM

I`d agree with Martin on this one, check cam timing or swap for something a bit hotter.

195 bhp from a 3.9 is poor as the 3.5 Vitesse produced these figures (admittedly with fuel injection).I can`t imagine lifter pre-load robbing you of that much bhp.

You could alter timing to 10 degrees btdc. and see how that is I ran my tuned 3.5 at 10 degrees and it ran nicely. I`d expect 230bhp from a well tuned 3.9 at least, but you may pay the price in torque figures.

Tony. :)