When Valve Shim Clearances Are On the Loose Side ?

Hi everyone,

Have just done a clearance check on my valves, at 27k miles. I don't know if they've ever been done before. I am a bit puzzled by the results.

Inlet range is given as 0.11 to 0.15.

I have readings of 0.15, 0.16, 0.15, 0.15


Exhaust range is given as 0.16 to 0.20

I have readings of 0.22, 0.21, 0.21, and 0.19.


So out of 8 readings, half are out of spec, but on the loose side. Isn't this the opposite of most people's experience ?

I am using a comprehensive set of metric gauges. Basically I used a go/no go method, rotating the cams say 20 degrees either side of ''bottom dead centre''. A bit tricky actually to ''see'' the point at which the cam was correctly perpendicular to the shim face. I'm pretty confident I got it right though.

I know the effects of too-tight clearances have been covered here, regarding potential damage, problems with vacuum synching etc.

IS out of synch on the loose side detrimental to properly synching the carbs ?

Appreciate any thoughts...

 

I'm betting somebody before you believed the wrong numbers in the Haynes and used .16mm~.20mm for the intakes too. (Which is wrong.) It would explain the intake measurements, even the "in-spec" ones (having tightened up from .16.)

Suspect PO shenanigans and put them all in spec.

Check again in 5K miles as recommended, and see what happened. I'm betting nothing (I have a 27K miles 550 and it is now holding clearances somewhat surprisingly.)

 

Hi bigfitz, thanks for taking the time to reply.

I assume the Haynes mistake you are hinting at is in the 650cc/750cc book, as my Haynes states 0.11-0.15mm for the intakes, not 0.15 to 0.20mm. Quite possible a PO was chancing their arm that the specs would be the same as for the 900cc, I suppose.

Anyway, what should I do about the exhaust side, with three out of four being on the loose side ? For peace of mind I will change those to bring them within spec, but will it achieve anything for me regards to vacuum synching ?

Are they causing damage ? Or signifying another problem maybe ?

 

Yep, I was referring to the 650/750, book, as well as the fact that the bogus spec gets passed on as correct on occasion.

Who KNOWS what a PO was thinking?

I would definitely bring them all into spec; and then check them at the recommended intervals.

As for the effect on your vacuum sync, any time you change a shim you'll throw your current vac sync off a tad. That's why the factory insists that the valve clearances be in spec before doing the vac sync. On the upside, it won't throw it off far (you will be able to notice) making it very easy to bring back into sync.

I doubt you're doing any damage but I'd get them in spec.

 

Will do. Thanks again for taking the time.