something is hanging up. newly rebuilt engine. vacuum gauge reading ~5 instead of ~18psi. Pulled the head and dismantled valves, polished valve stems and they spin nicely in the guides. Rocker arms spin smoothly on new bushings but occasionlly catch and don't close. The cylinder head has been shaved 100 thousands. The cam is ETC 7128 pushrods are slightly shorter than the originals for this engine but spec for this cam. I've polished the sides of the rockers and washers and pedestals. Tappet clearance is 10-12 thousands. If anyone has an idea of what is wrong, please let me know. I really don't know what to do to correct this problem. Thank you.
S2a rocker/arm hangup?
- Thread starter Samoth
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Tall Ratbag
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I would look carefully at the pads where the rocker contacts the top of the valve stem.
If there's a wear lip on this oad, that could stop the rocker returning freely - especially if the rocker geometry has been changed a bit owing to the head skim.
If there's a wear lip on this oad, that could stop the rocker returning freely - especially if the rocker geometry has been changed a bit owing to the head skim.
Thank you for that idea! Will check it out.
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Is this one rocker, or all of them? And it's definitely the rocker catching - so a loose pushrod? Just thinking that a damaged follower slide was more likely?
steve2286w
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Apologies for being a bit numptyish
Not sure what you mean by hanging up, can you expand on this
A tenth of an inch seems extreme to machine off cylinder head are you sure on this
And what have you measured the vacuum on
Not sure what you mean by hanging up, can you expand on this
A tenth of an inch seems extreme to machine off cylinder head are you sure on this
And what have you measured the vacuum on
It was 7 and 5(?). Pushrods are still straight. When I had the head off the engine turned over easily and looking down the lifter bores the lifter slides looked free and moved smoothly visually. I dribbled more Lucas assembly lube on the pushrods when I put the head back on. When I take the rocker assembly off in a few days I will check all the rocker pads and clean off any wear patterns or ridges. Thank you for responding. It's great having some support on this problem that I have been battling for a number of months now!
The valves seem to be sticking or slow closing. When setting tappet clearance I had several stay open partially. Then when I tapped on the adjuster it snapped shut. So I thought maybe there was too much friction where the rockers contacted the spacer washers and the pedestals and I polished the rocker side and washer and pedestal sides on 5 and 6, and 7and 8. Yes I had one hundred thousandths milled off the 7:1 head to give me about 8:1 compression. I have a vacuum gauge mounted on a fitting on the intake manifold over the cylinder 3 area. I appreciate your questions it helps me to think about it all. The engine starts right away and stops without running on. I've had the timing cover off 4 times trying to make sure the valve timing is right. This last I purchased a new cam gear and timed it off the cam key notch and the gear mark on the block as shown in the manual.
Well now I have the rocker assembly on the bench. And your right all of the pads have flat wear areas and looking closely there are also small ridges on the inner edges of the flat areas as well. I'm thinking that could account for valves not closing completely or rapidly enough. What do you guys think? Can I work out the flat areas on a flat surface with wet/dry sand paper sort of rotating the rocker pads over the paper with some oil? This is good. It gives me something positive to do!
Tall Ratbag
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It might be worth looking into fitting hardened valve stem caps. It all depends how bad the wear ridge is.
I've hand worked two of the rocker pads with 400 wet/dry paper and oil,keeping the curve on the pad. That eliminates the ridges easily enough leaving only a little residual flat area. How does that sound to you. Thanks for your help.
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They may be case hardened, and you may find the wear accelerating. (Start a fund for new ones).
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steve2286w
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I did that with mine and lasted a fair while but the valve stem top caps I used on the rebuild , can’t think that would be your problem though
I find it hard to believe that a valve spring can not overcome some slight friction/stickiness in the rocker arms.
But yet the engine runs fine, you say.
You say the valves spin freely (during rebuild) do they all move in/out freely in all rotational positions? I.E do you have a couple of bent valves in warn guides?
Be interesting to find the cause, I don't know the engine but its pretty basic, so watching. Wishing you luck.
J
But yet the engine runs fine, you say.
You say the valves spin freely (during rebuild) do they all move in/out freely in all rotational positions? I.E do you have a couple of bent valves in warn guides?
Be interesting to find the cause, I don't know the engine but its pretty basic, so watching. Wishing you luck.
J
steve2286w
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Interesting link here on pushrod lengths
www.landyzone.co.uk
is there an 8 on this cylinder head!?
Hi all, trying to work out compression ratio on my 1972 Series 3. Clearly has the raised level but can't tell whether there is an 8 stamped in (see arrows), or its just rusted that way?! Welcome any thoughts. TIA
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Thank you, I'm still trying to figure out the issue, but i agree with you.
According to Terry Ann pushrods for an 8:1 compression engine should be 7.175. The pushrods I have are 7.1875 or 12.5 thou longer. Maybe mine are too long? But I had room or space to set tappet clearance at 10-12 thousandths?Interesting link here on pushrod lengths
is there an 8 on this cylinder head!?
Hi all, trying to work out compression ratio on my 1972 Series 3. Clearly has the raised level but can't tell whether there is an 8 stamped in (see arrows), or its just rusted that way?! Welcome any thoughts. TIA
The engine runs very rough like stuck valves or bad valve timing
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Yes, insignificant.
