Valve clearances

Re5Guy

Re5Guy

Junior member
Location
New Zealand
Hello all,

As part of the process of getting my RGS Corsa on the road I have just checked my valve clearances and they are all tight with those for the centre Exhaust and Inlet valves needing quite small shims to get back to spec. The bike has only done 12,000kms so I was not expecting that at all. I have no idea of the bikes history. It has been sitting for some 30 years. The engine is in very good condition internally, nice and clean.

L to R123
Ex Measured valve clearance0.2300.1800.190
Measured shim size0.2500.2450.265
required shim0.2300.1750.205
In Measured valve clearance0.1500.1100.160
Measured shim size0.2500.2500.255
required shim0.2000.1600.215

Should I be concerned? It looks like I can get the correct shims from Precision Shims in Aussi.

Also the lower central exhaust camshaft holder is lightly scored, I can feel the roughness with my finger, It looks like a piece of sh*t has got in there, the cam is fine and the upper holder is fine as well as are all the other holders. Should I consider replacing it/fixing it/or it'll be fine....?

cheers

Tony
 
You've got something very wrong there...

Standard shim thickness started at 1.75mm and went to 2.80-2.90mm. New engines left the factory with shims in the 2.50-2.70mm range. I think you've misplaced the decimal point. Review that and re-calculate, you will find the shim sizes to all be in the ballpark. I'm aware rotaries don't have poppet valves, but it's not rocket surgery. ;)

eg, exhaust #2. Measured 0.18mm, needs 0.07 less to get it to 0.25mm. Shim goes from 2.45 to 2.38mm.

I've always adjusted valve clearances to the upper tolerance limits, ie, exhaust 0.25-0.30, inlet 0.20-0.25mm. Affords a lot of piece of mind when on long trips and I'm too lazy to check en route.

Not at all uncommon to find scoring in the cam bearings, testimony of slobbered oil changes... beats me why hardly anybody adhered to the 2500km change interval. Cam bearing clearance is quite generous, light scoring won't have much effect.

piet
 
Duhhhh....of course, looked at it for ages thinking something's not right.... sometimes the more you look the worse it gets 'cos you get stuck on one idea.

Glad I decided to open it up for those with an intellect greater than mine. Thanks for that short piece of enlightenment Piet.

What's wrong with screw and locknut, that's what I want to know!!! 😆
 
You mean screw and locknut on the valves?

On a DOHC it's physical engine height, space is at a premium in most bike frames of the period. Valve and intake angles are also limited by these old frames. Look at all the changes that have been implemented since cradle/backbone frames have been ditched!

The shim-on-valve sytem is tried and tested in countless hi-revving racing engines. No red-blooded italian engine designer would tolerate those half-arsed shims-in-tappets or even rocker arms in such an engine... live with it. ;)

piet
 
Re5Guy said:
Yep all true, but Kawasaki managed it with their GPZ900 of the same vintage...just saying
Click to expand...
That’s because most Japanese people have small hands, if you’ve ever adjusted GPZ900 tappets, you’ll know what I mean.

Signed
Bare Knuckles

PS: It took Kawasaki no time at all to realise the oil flow to the GPZ cams was inadequate and caused premature pitting, hence the larger oil galleries on later models.
 
chrisk said:
PS: It took Kawasaki no time at all to realise the oil flow to the GPZ cams was inadequate and caused premature pitting, hence the larger oil galleries on later models.
Click to expand...

Not all was milk and honey that came from the Land of the Rising Sun... for all the awe and hype that surrounded them, jap bikes also had their fair share of issues. Older survivors usually also show much the same symptoms as old italian clunkers, which goes to show that not even japanese engineers could defy the laws of physics, cue, "superior engineering techniques".

piet
 
I'm notoriously bad with arithmetic, so I work out what shims I need on a spreadsheet. That way I'm less likely to fuck up.
If I was to do it in my head, there's a pretty good chance I'd get at least one of the 6 wrong. It's even more of a challenge when I do my Kawasaki Z1300.

The useful thing about having everything on a spreadsheet is that you can record the date and save the file for that service. You then have a record of what shims went into each bucket, and you can easily monitor any changes next time you do it. Knowing what shims are in there is handy next time you do the clearances because you can work out what shims you need before removing the camshafts. If you don't have the required shims, you can slap the lid back on the engine and keep using the bike while you wait for your shim order to arrive.
 
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