9 replies to this topic

[racingbob]

I thought I saw some 25 thou shims to go under rocker posts for heads that have been skimmed

 

but now cant find them on minispares website

 

also when is it you need to fit as far as thou taken off the head

 

I see there are some of the 50thou ones for the top of rocker post

[Batmini]

Shims for the top of the rocker posts? I thought you only had to shim UNDER the rocker posts (2A515) and this was only if you had machined a lot off the block/head. It is just so you can easily adjust the tappets.

[Wim Fournier]

Question is, how far the valve seats have worn already. The deeper they are the less thread remains on the tappets to adjust. In the end the valves don't shut anymore.

[racingbob]

Shims for the top of the rocker posts? I thought you only had to shim UNDER the rocker posts (2A515) and this was only if you had machined a lot off the block/head. It is just so you can easily adjust the tappets.

2a515 looks like its for the top

 

but you could put them under if 50thou was off the head

 

I think MED do a shim

[Dusky]

Shims for the top of the rocker posts? I thought you only had to shim UNDER the rocker posts (2A515) and this was only if you had machined a lot off the block/head. It is just so you can easily adjust the tappets.

2a515 looks like its for the top
 
but you could put them under if 50thou was off the head
 
I think MED do a shim

or just read the description. Spacers for under the rocker pedestals are used mainly by engine tuners to allow tappet adjustment to be made where cylinder head mods have been carried out. 1.3mm/0.0512" thick, this can be used to hold locating screw on rocker assembly but the centre hole will need elongating to accept 2A258 screw.

[nz_seamless]

I thought I saw some 25 thou shims to go under rocker posts for heads that have been skimmed

 

but now cant find them on minispares website

http://www.minispare...ries/2A515.aspx

 

And they go under the rocker pedestal, not above. If you stick them above the pedestal all you are doing is spacing the nuts further up the stud thread. You won't need that unless you have some oddball pedestals or unnecessarily long studs.

 

Under the pedestal moves the rocker adjuster further away from the rod, which is needed if you have taken material off the head/block, thus shortening the rod/rocker distance. On mine I have two sets of shims, otherwise the adjusters were screwed right up into the throat of the rocker. The shims bring the ball of the adjuster out to where it should be on a stock length arrangement.

Edited by nz_seamless, 27 November 2015 - 01:55 AM.

[Batmini]

Shims for the top of the rocker posts? I thought you only had to shim UNDER the rocker posts (2A515) and this was only if you had machined a lot off the block/head. It is just so you can easily adjust the tappets.

2a515 looks like its for the top
 
but you could put them under if 50thou was off the head
 
I think MED do a shim

I think you are misunderstanding their purpose. As per my previous post, they go under the rocker post and are only there to give you enough adjustment on the tappets if you have had the head or block skimmed.

[Earwax]

a further and reasonably common purpose these days is to correct the geometry on 1.5 rockers.  It seems a number of different types ( titan and HS) know this required but still don't include when you purchase. ( in other makes/ and bespoke fit outs it is more common to adjust the length of the pushrods to achieve this geometry....but that is a digression)  i just think it would be better if the makers included their own shims at least as an option -  sorry racingbob doesn't help but if you go to race mini builders i am sure they get them made up

[jaydee]

Actually their purpose is to optimise the rocker geometry, essential with high lift rockers that have short posts.

By adding the correct spacers the rocker can sit at 90°vs the post when its at half lift.

[tiger99]

Yes, exactly, and if you use them for the other purpose of compensating for a severely skimmed head you will often get very incorrect rocker geometry, and increased wear, with some loss of performance possible. Using shims under the pillars for that purpose is just plain wrong.

 

If the head has major skimming, you really do need shorter pushrods, although a cam regrind, plus grinding the tappet faces so the bottom of the tappet was at its minimum acceptable thickness, could possibly help to achieve the same result. A little bit off here and there might add up to what is needed.

 

This is true on all conventional overhead valve pushrod engines with the camshaft(s) in the block, not just the A series.