Tappet / lifter preload

[Tobs]

How important is getting the preload correct?

I am under the impression that it is only done to stop the possibility of the lifter pumping up at high RPM. So the preload is set to only allow a max of 0.5mm or so of movement.

I am asking this as I have recently fitted a new cam / lifters / rockers. I set the pre-load as best I could, ending up with I think 40 thou shims under the rocker posts. However I am still getting some valve train noise (better than before I changed the cam which had 2mm missing from some lobes) See my other thread on this.....

If I was to remove the shims, to see if this quietens things down at all would this cause a problem? My only concern is that the lifters will initially be more pumped up than they should be after i remove the shims - will they empty themselves of a bit of oil?

Edited by Tobs on Wednesday 2nd May 11:39

[jonnyb]

Im not an expert, but I have just changed the cam on mine and after 3 days of trying and failing to set the pre-load I still have some valve train noise. At this point a phoned a few engine builders and TVR Power to ask their opinion. None said it was an absolutely vital operation, two said as long as it is a road going car and unlikely to rev over 6000rpm then they wouldn't bother. One TVR indi seamed quite surprised I was even asking.

According to V8D and RPI it should be done but they didn't say how important it was. I don't think TVR Power did it when they built the engine, or according to them they didn't as it should all be within tolerances. And I didn't find any evidence of the pre-load being set when I striped the engine.

Best bet is to phone the people you got the cam off and have a chat with them. They will be able to point you in the right direction.

I am going to see how the car goes and if the noise starts to get annoying then V8D may well find me on their door step so have it set correctly.

[GreenV8S]

Tobs said:

I am under the impression that it is only done to stop the possibility of the lifter pumping up at high RPM.

Obviously you *must* make sure there is some preload, but you only need enough to cope with thermal expansion.

Preload is usually set dry, I don't know if it is absolutely necessary but I think the advice if the engine has already run is to dismantle and empty the lifters before trying to set the preload.

[spend]

Are your valve springs matched for your new cam, did you check they were still good? (PITA if you didnt pop the heads tho ) Its better if you can to get all kit from single supplier who should make sure they are all suitable + give any advice you need IMHO.

Dave

[Tobs]

Yes, new springs supplied with cam (MC1 from V8Dev). Your right PITA to change with the heads on - esp the most rearward OS one!

[2Munkys]

I'd have thought that if the base circle of your new cam is the same as the old and your lifters and rockers have been replaced with like for like then there'd be no need to shim.

[Tobs]

2Munkys said:

I'd have thought that if the base circle of your new cam is the same as the old and your lifters and rockers have been replaced with like for like then there'd be no need to shim.

Yes should be the case - the shims just reduce the ammount of movement left in the tappets, to reduce the ammount they can pump up.

I think I am going to just remove the shims and try it to see if it makes things quieter. I think the new rockers I bought are not the best quality, as they seem to have varing depths of cutouts for the pushrods - this means that there was a large variation in the preloads. I think I may put my old rocker assemblies back on as well as removing the shims (they are not too worn anyway).

[GreenV8S]

Tobs said:

Yes, new springs supplied with cam (MC1 from V8Dev). Your right PITA to change with the heads on - esp the most rearward OS one!

Curious, I've not found that to be a problem on the V8S. Does the bulkhead get in the way on the Chimaera?

[Tobs]

GreenV8S said:

Tobs said:

Yes, new springs supplied with cam (MC1 from V8Dev). Your right PITA to change with the heads on - esp the most rearward OS one!

Curious, I've not found that to be a problem on the V8S. Does the bulkhead get in the way on the Chimaera?

Yes, the bulkhead is quite close, as well as the bonnet catch mechanism (still got the marks on my hand from the frayed cable!), the heater pipes (on the serp engine), and fuel pipes. All seem to be in that region!

[captiv8ed]

I've just done mine, as I've fitted a shiny new stealth cam. I used 2 bits of welding rod, 45 and 60 thou. All but 3 tappets came in this range with the 34 thou shims. I spoke to Ray at V8D and he advised me that the tolerances are 20 - 80 thou though 50-60 is ideal.

I reckon my 3 that were higher were about 70. Remember the rocker ratio of 1.6, so your 40 thou shims actually raise the gap to 64 thou!

[rev-erend]

I've always found this preload business a bit confusing ..

So - what the heck I just called V8 Developments and luckily I don't need to do it on my engine..

Think I'll just check the valve lift is correct on all at 12.827mm though

[spend]

rev-erend said:

I've always found this preload business a bit confusing ..

So - what the heck I just called V8 Developments and luckily I don't need to do it on my engine..

Think I'll just check the valve lift is correct on all at 12.827mm though

Good, I know where to send the contract engine strippers now

Dave

[rev-erend]

spend said:

rev-erend said:

I've always found this preload business a bit confusing ..

So - what the heck I just called V8 Developments and luckily I don't need to do it on my engine..

Think I'll just check the valve lift is correct on all at 12.827mm though

Good, I know where to send the contract engine strippers now

Dave

Don't tell the g/f but the engine in hiding under the coffee table..