Rocker arm shimming clearance question

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fid04

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Nov 12, 2022
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Just got my head serviced with new valves, guides and springs. All rockers had the spring/shim. One had 3 washer shims, the rest had one. Doesn't look right to me. What are thoughts on using, vs eliminating the spring/shims and just using just solid shim washers? What should the end clearance be, and should the rocker be centered over the valve stem? Any other information about installing the rockers is welcome.
 
The reason I like the stock Thackeray spring set up is that it makes it easier to assemble the head especially when it's 200 or more degrees. I assemble it cold with an undersize spindle.
Fiddling with spacers and shims gives the opportunity to align the rocker tip to the valve stem but it would be a lot of work for maybe a minute gain. Count me out.
 
I am running solid shim washers on my Commando. I used to have them on my Dominator, but I have had the head apart a few times in the last few years, and like seattle##gs says, they are a bit of a pain to align and install, so I decided to go back to Thackery washers. Initial install takes time and patience, each shim has to be ground down to size. I probably spent an hour or more on each one, grinding them to size by hand with a high quality fine grinding stone.

I do not notice any difference is noise. I think there is probably a slight reduction in friction with the solid shims. If you have the time and patience I don't think there is any overarching reason not to use them?
 
Last edited:
fid04 said:
Just got my head serviced with new valves, guides and springs. All rockers had the spring/shim. One had 3 washer shims, the rest had one. Doesn't look right to me. What are thoughts on using, vs eliminating the spring/shims and just using just solid shim washers? What should the end clearance be, and should the rocker be centered over the valve stem? Any other information about installing the rockers is welcome.
Click to expand...
I wish you were a Premier Member so I could PM you as I really don't need the feedback that will likely come from this:

The thin flat washer goes on the outside of each rocker. Unless someone has modified the rockers, there must be only one.
The spring goes on the inside of the rocker by itself.
The adjuster is NOT supposed to be centered on the valve stem. If very far off, suspect that someone before you has "fixed" the rocker.


A very famous race engine builder likes the adjuster dead center on the valve stem and no spring washer. He grinds the rockers and adds flat washers as needed to make that happen. I obviously disagree.

Some here also don't like the spring washers and have other solutions. I obviously disagree.
 
General end float, for crankshafts, camshafts in cars . 002"-.006". I'd say 4-5 thou would be fine, if you go that way. I had to file some oil grooves into mine, to help lube my exhaust valve, but that was an old BSA b33, not many original parts on the inside 🤣🤣. Cheers
 
marshg246 said:
I wish you were a Premier Member so I could PM you as I really don't need the feedback that will likely come from this:

The thin flat washer goes on the outside of each rocker. Unless someone has modified the rockers, there must be only one.
The spring goes on the inside of the rocker by itself.
The adjuster is NOT supposed to be centered on the valve stem. If very far off, suspect that someone before you has "fixed" the rocker.


A very famous race engine builder likes the adjuster dead center on the valve stem and no spring washer. He grinds the rockers and adds flat washers as needed to make that happen. I obviously disagree.

Some here also don't like the spring washers and have other solutions. I obviously disagree.
Click to expand...
Seems to be different schools of thought on the subject. Curious if you have ever put any kind of reference mark on the side of the valve stem to test out your theory and see if they do indeed turn.
 
Way back, in Comnoz’ fabulous ‘spintron’ thread, he suggested that the Thackeray washers probably provide a small damping effect to the rocker which would be beneficial for valve control, especially at higher rpms.
 
fid04 said:
Seems to be different schools of thought on the subject. Curious if you have ever put any kind of reference mark on the side of the valve stem to test out your theory and see if they do indeed turn.
Click to expand...
You can look at the wear pattern on the valve stem and see that they do.
 
C

Post in thread 'Thrust washers on rocker shaft'

marshg246 said:
BTW, IMHO, centering the rocker is bad - the valve is supposed to turn.
Click to expand...
I have only seen the top of used valve stems with one straight line scratch marks caused by the valve adjuster contact. There is no way for a valve to turn and there is no evidence that I have seen that they do. I like to see nicely centered valve stem to adjuster contact. And use bronze spacers instead of the Spring "washer" as they call it in the parts book. And different thickness "thrust" washers to get minimum end play. They can be had in 15 and 30 thou.
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https://www.accessnorton.com/NortonCommando/thrust-washers-on-rocker-shaft.40994/post-700245
"I just looked at maybe 20 old valves, and they all have linear wear marks.
They did not rotate."
 
I don’t believe replacing spring washers with shims, on a rocker shaft make a Commando go faster. It just seems like a “racing” thing to do.

I’m not clever enough to pass a judgment on centre or off-centre valve tip contact.
 

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