Valve clearances keep changing

[bnam]

I'm reassembling my engine and have got to the part where I'm setting valve clearances. I've not changed the head or valves. I have changed the adjusting screws for new one from Aircooled as the old ones were a unevenly worn/flattened.

I set each cylinder (going 1-2-3-4 per Bentley) to 0.006". But when I recheck after turning the crank a few times, the clearances changed. So re-did them again and checked again. Even now, sometimes I'll get a 0.007 on a valve even though I had set it to 0.006".

I know the screws do not contact the valve ends in the center, but are offset to cause the valve to rotate. So could it be that the ends are not evenly worn and sometimes I am getting a low point reading? Just a wild guess.

Anything else I should consider?

If my guess is right? Is it better to set it so that it varies from 0.005 to 006" or from 0.006-0.007?

Thanks!
Byas

[Boolean]

You are on the right track. The base circle of some cams does not give the same lash all around. Just check so it isn't too tight somewhere. .005 is fine with the stock cam and pushrods.
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[FeelthySanchez]

Using a stock pulley? If so, it's easy to miss the exact mark (base circle) for a couple valve positions.
Using some new parts: they're not yet broken-in/seated.
1 thou extra clearance is nothin' to sweat over, & better a bit loose than tight.
Of course, all will change after the fires are first lit: when she cools-off, don't be surprised to find them loose again.
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[mark tucker]

cam fles and flex of the rest of the system, do it the preload method.

[FreeBug]

Brand new engine? You're wiping the assembly lube off the cam, every tunr a little more..

[bnam]

Thx!

It's the old original engine on my 71 T1 vert. Got slightly over 100K km (60K+miles) on the bottom end and 25-40K kms on the rings and valves (pistons/cylinder/head are original).

BTW, what is the pre-load method?

Byas

[mark tucker]

when the ex valve is about 6-8mm down you adjust that cylinders intake lash. turn the crank till the intake valve go,s down then starts coming back up and stop around 6-8mm before it is closed and then adjust that exhaust valve next to it. this accounts for flex and wear&other clearances in the system.

[modok]

[richparker]

I was taught to adjust the 4,3,2,1.
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[gt1953]

Set them and start the darn motor. Break the cam and lifters in and let us know.
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[bnam]

[Boolean]

You are overthinking it. The engine will run fine with even double lash.
Just adjust so it's not too tight. Run it a while and readjust as necessary.
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[bnam]

Agree. But, I am still curious as to why there is so much variance. Engine was running well before, so not concerned about that. But, I did feel in the past that even after adjusting the valves, I was hearing a bit of valve clatter. Perhaps this variance explains that.

Only valves which have high variance are #1 and 3 intakes. Where I've now set them to 0.004" at TDC which then opens up to 0.008 at the preloaded measurement. With this range, I was shooting to be 0.006+/- 0.002". Any other setting causes it to be either too tight or too loose at one of the measurements.

[modok]

what is the clearance of the cam in it's bearings?

[FeelthySanchez]

Given: " .... 25-40K kms on the rings and valves (pistons/cylinder/head are original)".

Have to suggest that the valve guides & possibly seats are worn.
Also, disassemble both heads (but keep valves indexed) & check for a loose valve GUIDE.
I had the same symptoms in late '90s on mamma's last Beetle & it drove me nuts - until I saw the loose intake guide: which had worked itself half-way up to the spring retainer!
Pulled that head & springs, noting that same guide was not even finger-tight in the head - was actually RATTLING in the guide boss.
G' luck!
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[bnam]

Glen,
I didn't split the case - so don't know the clearances at the bearing. Engine has 100K kilometers on it. I don't believe the bottom end was ever rebuilt. I drive it about 1000K/year now and engine runs well enough that I was hoping not to have to split he case. Crank end play was ok. But, pistons/rings are at the limit of their wear -- so that's on my list.

I just looked up this pic from the gallery. #2&4 intakes and #1&3 exhausts are all very consistent -- with almost no variation. If the variance on #1&3 intakes were caused by play in center bearing for the cam, should it not show up on #2/4 intakes as well?


Byas

[modok]

????
If you want to know, take the rockers off one side and try it again.

This will eliminate the variable, as the cam will stay pushed only to one side.

I don't know. I do know the average clearance of the cam bearings, in a old engine .003-.005 From this I assume the position of the cam, at any given degree, is, in technical terms
"wobbly as all get out"

I don't think you are the first guy to obsess about it, might be interesting to compare with the last guy, but I don't have much hope of finding the others with search. Not sure what keyword to use. Lash....variation?

[bnam]

Will try that out this evening. THx!

[Volks Wagen]

[bnam]

I did not disassemble the head this time as I didn't have the spring compressor tool. So worn seats, tips, valve play in guide are all still possibilities plus modok's suggestion of cam bearing as well. I'll try to do the cam bearing check by pulling off the opposite rocker as he suggested. My initial thought was worn tips due to the beat up adjusters that were on there before.

I did measure the piston/rings clearance and they are at the limit or just beyond. So do need to replace those in the future and will slowly get the parts together. Will also get valves and guides and redo seats at that time. Plus the Pistons are the low compression (6.3:1 option m240 ones) -- will go with regular pistons and get the 4 more hp.

One more question -- how much does a valve rotate on each cycle? I had read that the screws don't contact the tips centrally, but are offset to rotate the valves and create even wear in the seats. Since the high and low readings are not random but periodic - tight at TDC and loose at preload an unevenly worn valve tip that rotates just the right amount each turn could correlate with that.