Orangebean wrote:
Marty- I've just had a look at the RPI instructions (interesting- hadn't looked at these in detail) and I think you might be introducing a "fudge factor" into your measurements, which could potentially mean that you'll find it hard to get consistently repeatable results. I've picked out the problem area in bold:
"The following information assumes that the following components are in good condition - rockers, pushrods, valve guides and valve stems. a clearance of .020" to a maximum of 0.60" must exist between the spring loaded pushrod seat in the top of the lifter, and the underside of the retaining circlip. This check should be made with the valve gear fully assembled, and the lifter empty of oil, positioned on the lowest point, on the back of the camshaft. The simplest way to measure the gap is by using round wire. Use a piece .020" for the low clearance check, and a piece of .060" for the high clearance check. Check all 16 lifters individually."
You've primed your lifters and also they're skating on a raft of assembly lube. Both of these will give a variable cushion. The RPI instructions are based around a dry build (actually a pre assembly with only a squirt of light oil on touching surfaces). I'm going to pop over to V8 Devs site and have a look at what they say and will come back in a bit...
Orangebean wrote:
Well, if it were me.....
I like the V8 Devs way of measuring preload. Does the same thing as RPI only without bits of welding wire, just by using feelers under the pedestals with pushrods free spinning.
First thing to bear in mind is that the whole point of having hydraulic tappets is that you don't have to be accurate, the tappets do that for you. As long as you stay in the range and don't either have too much free play with the tappets at full expansion, or too little with the tappets empty, they'll just do their stuff.
Anyhow, get together a set of pushrods that are as close to the same length as you can. Use the V8 Devs method of checking preload. (Pedestal gap measurement x 1.6 = Pre-load at follower).
Shim rockers with equal sized shims to suit. Job done.
If you want to get really (poss pointlessly) precise, don't forget that you can buy shim steel in A4 sheets and cut out shims with a pair of scissors and a hole punch, in 1 thou increments (from 1 to 10 thou naturally- anything bigger requires special tools) :)
Oh and by the way, if you're going to cling wrap the block, and it's in your house garage rather than workshop, let it breathe!
When are you back from next trip? I'm happy to pop up and play clearances with you
Thanks for the information - and also the offer to come up.. I'll have another look over the weekend and if I'm not happy, then I'll drop you a message and we can work something out..
Yes, I think there is somewhat of a 'fudge factor' in my readings, also from looking at the RPI instructions and about everything being dry, whereas everything in my engine is somewhat moist now...
I have actually been doing a combination of the 2 methods.. the V8 Developments method only states doing it for the number 1 cylinder, rather than every tappet/pushrod, so my method was to get the no 1 cam lobe 180deg off, and then tighten down the rocker shaft slowly. I also used feeler gauges to make sure that at the point where I was seeing the tappet piston be depressed that all the rocker pedestals were the same distance, I didn't want one end of the shaft to be not as tight as the front, otherwise that would distort the geometry aswell. Once they were all pretty close, I tweaked the front one down a nudge until it started depressing and then measured the gap with the feeler gauge. (This was also after pulling the rods/tappets and checking them for length etc)
On the LH bank (well, RH as I'm looking at it from the front - but cyls 1,3,5,7), this was 0.05" - which with the 1.6 factor, would mean my preload on the tappet would be 0.08" if it were bolted all the way down. If I were aiming for 0.04", then I would need 0.04" off the preload, which then divided by 1.6 would give a shim height of 0.025". As I have 0.015" and 0.03" shims, I opted for the 0.03" and fitted them to all the pedestals. With this done, I then went through the RPI method and turned the engine by hand so every tappet in turn was opposite the cam lobe, and then did the feeling with the welding wire feelers I have (after giving them a file so they were a bit more accurate. This is where I found that the LH bank were all pretty close to each other.
Swapping to the RH bank (LH as I'm looking at it from the front, or cyls 2,4,6,8) I did the same - turned cranks so inlet valve was closed and tappet was 180deg from lobe. Tightened shaft down slowly and measured with feeler gauge, as the tappet piston was starting to be depressed, and got a reading of 0.061" - which with 1.6 factor gave a preload of 0.976". A bit more than the other side, but again worked back and to give an ideal preload of 0.04" I would need a 0.036" shim - so again opted for the 0.03" shims.
Fitted the shims and then measured, and the front 4 valves all were pretty much bang on 0.04" when I went back and did the RPI method - but getting to the rear 4 rockers/tappets is where I found that there was no preload at all. From there I decided to swap the shims for 0.015" and now get 30-40 thou on the rear 4 and 60-70thou on the fronts...
So.. my current thought... I'm going to leave the LH bank (cyls 1,3,5,7) alone... it's close enough now, and more than likely a lot better then if I'd just chucked it together without checking the preload and hoping for the best...
BUT - on the RH Bank (cyls 2,4,6,8) - I have an option... given they are about 30thou out.. do I just leave it, and as you say - they are hydraulic tappets, so will they take up 30 thou within them when it's up and running? Or do I see about getting/making some say 20 thou shims to split the difference and at least try and even them up?
Regarding leaving it - yes, the engine is in the garage at home, rather than the workshop. Once it's finished being assembled, I'll crane it into the back of the RR to take it to the workshop and then do the swap over up there. If it's worth leaving it open to breathe, then I have a sheet or cardboard that I can leave over it to prevent anything getting into it - though it also would absorb moisture, so maybe not... I can loosely clingfilm it..
I am back from the next trip just before Christmas - I head away next week at some point, so after I've got what I can done, she'll be stored on the stand in the garage until I get home, at which point I'd like to be ready to do the final assembly, and then get it loaded up and swapped over!
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