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Author Topic: Piston hitting Exhaust Valve when Valve Lifter is engaged.  (Read 5682 times)

Delatite

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Piston hitting Exhaust Valve when Valve Lifter is engaged.
« on: September 22, 2006, 09:04:19 AM »
Hi
I have just finished restoring my Lister 3/1 and turned it over this afternoon for the first time. It turns over fine when the valve lifter is not engaged but as soon as I engage the lifter the piston hits the exhaust valve. Does anyone have any idea what may be the problem. The head was in very
poor shape and that was machined maybe thats the cause. Until I talk to the machinist on Monday I don't know how much he shaved it.            Head to piston clearance is set to 0.055" a tad more than the Lister reccomended 0.050". I removed the valve lifter pin from the valve lifter and that seems to have fixed the problem. Any input would be appreciated.

Thanks
Brent

emerald

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Re: Piston hitting Exhaust Valve when Valve Lifter is engaged.
« Reply #1 on: September 22, 2006, 10:55:47 AM »
It does sound like too much material was removed. Getting creative with a thin gasket under the block will help, its a little fiddly but done pretty often.

Emerald


Geno

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Re: Piston hitting Exhaust Valve when Valve Lifter is engaged.
« Reply #2 on: September 22, 2006, 11:44:19 AM »
If the head was shaved the distance between the decompressor and and head is less, increasing the chance of a collision. If piston to head clearance is ok I'd take some material off the bottom of the decompressor. If you take to much you can always shim it.

Thanks, Geno

Delatite

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Re: Piston hitting Exhaust Valve when Valve Lifter is engaged.
« Reply #3 on: September 22, 2006, 12:22:59 PM »
  By removing too much metal from the head I have effectively reduced the distance between the valves and the top of the piston. I feel this may be the cause of the problem. If I grind down the valve lifter pin so that the piston is not hitting the exhaust valve when valve lifter is engaged that should fix the problem. What worries me is that even though  the piston and  valves are not  hitting when I turn the engine over  by hand under normal running conditions they may be too close.

Thanks
Brent
« Last Edit: September 22, 2006, 12:25:11 PM by Delatite »

aqmxv

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Re: Piston hitting Exhaust Valve when Valve Lifter is engaged.
« Reply #4 on: September 22, 2006, 03:06:22 PM »
I wouldn't worry too much about that.  Lister used big rocker arms that rotate through a small arc with little lever action with pretty static geometry.  Also, the clearance adjustment is on the pushrod end, so it effectively changes the length of the pushrod, and not the fulcrum point, as is the case with many car engines.

In short:  If you fix the exhaust lifter problem and set the valve clearances to factory spec, you should have no problems.  A double-check is that the rocker arms should be pretty close to horizontal when the valves are closed.  If they're not, you have some altered geometry somewhere and should investigate.  It's all adjustable and repairable.
6/1 Metro IDI for home trigen

Geno

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Re: Piston hitting Exhaust Valve when Valve Lifter is engaged.
« Reply #5 on: September 22, 2006, 10:20:05 PM »
Since the relationship between the bottom of the head and the bottom of the valve has changed by whatever was was shaved off the head you may have a point. The valves will be that much closer to the piston. How much was taken off? Squish test it if your worried. I imagine some clay would work to get a good idea of whats there.

If you think the valve is to close with the decompressor engaged get the engine to TDC with the decompressor engaged and push down on the valve manually to make sure you get some movement. I would guess there is a spec for both clearances but I don't know what it is.

Thanks, Geno

snail

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Re: Piston hitting Exhaust Valve when Valve Lifter is engaged.
« Reply #6 on: September 22, 2006, 11:33:47 PM »
On the 6/1's there is a spec for the amount that the valves are sunk into the head.I could look it up I suppose, but from memory the inlet and exhaust valves are different.I'm sure that the 3/1 will have equivalent figures, and I'd have a look in one of the old manuals that are available online.
I trimmed the valve lifters on my 'roid, no problems!

Cheers

Brianl

dkwflight

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Re: Piston hitting Exhaust Valve when Valve Lifter is engaged.
« Reply #7 on: September 23, 2006, 12:11:52 AM »
Hi Double check the valve adjustments. I had mine out of spec and though I needed to modify the de compresser arm. It turned out not to be the case.
Dennis
28/2 powersolutions JKSon -20k gen head
Still in devlopment for 24/7 operation, 77 hours running time

Delatite

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Re: Piston hitting Exhaust Valve when Valve Lifter is engaged.
« Reply #8 on: September 24, 2006, 01:46:01 AM »
Thanks for the input everyone, I shall squish test it as Gino advised just to be on the safe side. ???

Thanks
Brent