Six of my valves are out of spec, too tight. Of the six, five were only .001 under spec, the sixth had only .002 clearance. The PO said he never had them done in the 15k miles he rode it. It has 22k on it.
Sorry, I don't measure millimeters as well, knuckle-dragger musclecar type here, you know, solid lifter cams in hotrods and all.
I quickly ran out of the correct size in my assortment, and swapped in some used shims from other valves as I went. All of the shims looked so good that other than the spacing of the mark on the shim, they were indistinguishable from new.
Conventional wisdom in the car world is that you never place a used lifter on a different lobe, and never put used lifters on a new cam. So after jockeying 4 of the six valves into spec, I began to wonder if I would kneel before satan for doing this.
Nobody within 100 miles had 25mm shims. The price of semi rural living I guess.
no worries....the shim material is very hard and as long as you get the correct clearances you will be fine.
dont kneel.....do KOokaloo!
Frank
Not a problem at all. Most engine builders have a shim exchange program when doing re-builds to help keep the costs down. Use 'em if ya got 'em!
Quote from: junkyardroad on November 15, 2009, 04:40:38 PM
Nobody within 100 miles had 25mm shims. The price of semi rural living I guess.
A few Honda motorycles used 25mm shims as do some Toyota cars. Bet you have one or the other witin 100 miles (unless you're in the middle of Death Valley :-)
Cheers,
Arnie
junkyardroad,
Take one automotive (car/truck) lifter.
Point the cam contact face up.
Now you are imagining that this face is flat aren't you? :negative:
If you take an engineers square to this face you will find it is ground with a convex dome,
i.e. with a slight curve, the centre being the highest point.
This achieves two things:
1) ensures that the lifter rotates as it is lifting so as to spread wear across the face of the lifter,
2) this rotating motion imparts more of a wiping action onto the cam and lifter prolonging the life of both.
If you have ever had a stuck lifter in a bore this is because the contact face of the lifter is flat.
The convex machining has worn away exactly like a burr forms on a chisel head. Also if you look
very closely at an automotive camshaft you will see the lobe finish is usually #100 and not polished.
This is to help impart rotation onto the lifter by grabbing the contact face. Imagine the number on
a piece of sandpaper, the bigger the number the smoother the finish. Well #100 is something like
that, very smooth but not polished.
The conventional wisdom spoken of goes back too many years and is fact not conventional anymore. :blush:
Many engine parts were foundry cast and then machined. But since the late 1980's both metallurgy
and oil refining processes have improved. For example, forging and heat treatment are very
common in automotive applications. Along with the improvement in oil stock and additive
packages there is now no reason at all to keep parts in any order except to continue existing mating
patterns, specifically big end and main caps.
:nea: I've only just opened up my FJ1100 but there is no engineering reason at all not to swap shims
around. My reasoning is that a shim IS ground flat in order to promote stable clearances. There is a
layer of oil between the bucket and the shim to help rotation of the shim. And my final assumption,
that the shims are machined from a length of forged rod, i.e. NOT cast.
Hope this helps alleviate any concern you may have. :good2:
Cheers
ren-dog
QuoteHope this helps alleviate any concern you may have
It does. I observed ALL the shim/buckets rotating a 1/8 to a 1/4 turn or so thru every valve opening, so I think the convex shapes are still intact.
The maching shop dude 'splained that the wear patterns between cam/lifters are unique to each and with modern spring pressures, eventually they chew each other up. Last time I tore down an engine that ate a cam lobe (396) there was inbed in every bearing in the engine. Very ugly. Just want to be sure.
Thanks