Valves loosening?

BrianK · Aug 5, 2009

When I got my 73 850 Commando a while ago, I adjusted the valve clearances (I don't think they were far off) to .008" exhaust and .006" intake.

I just rechecked them (it's been about 4000 miles) and all of them were LOOSER than where I'd put them, some by as much as .004". All of the locknuts were firmly in place and hadn't loosened.

I'm used to valves TIGHTENING with use, not loosening. Anybody ever run into this?

Thanks - BrianK

maylar · Aug 5, 2009

I can think of 3 possibilities:

1) Cam wear making the lobes shorter (hope not).
2) Valves not seating (you'd notice that in the way it runs).
3) Pushrods "settling in". This is possible if they were new when installed, or the end caps had been removed.

L.A.B. · Aug 5, 2009

maylar said:
1) Cam wear making the lobes shorter (hope not).

When the valve clearances are checked/adjusted, this is done with the followers on the base circles of the cam, so cam lobe wear does not affect the valve clearances.

BrianK · Aug 5, 2009

Thanks guys. Runs all right, especially for a bike that fairly badly needs rings, and possibly valve guides as well (right cylinder - 150PSI, left cylinder - 120 PSI dry, 180 PSI wet!). Guess I'll see if they continue to change over time. Maybe I just didn't do it right last time around - was my first time with screw-type adjusters, so perhaps that's all it is.

B+Bogus · Aug 5, 2009

L.A.B. said:
When the valve clearances are checked/adjusted, this is done with the followers on the base circles of the cam, so cam lobe wear does not affect the valve clearances.

However, wear on the followers will result in increased valve clearances.
/pedant mode

maylar · Aug 5, 2009

L.A.B. said:
maylar said:

1) Cam wear making the lobes shorter (hope not).

Click to expand...

When the valve clearances are checked/adjusted, this is done with the followers on the base circles of the cam, so cam lobe wear does not affect the valve clearances.

Duh. My bad.

daveparry · Aug 5, 2009

Maybe you didn't have the followers on the base circle of the cams when you adjusted the clearances?

BrianK · Aug 5, 2009

Certainly possible. In any event, operator (me) error does seem the most likely cause.

Buttoned her up after the adjustment, started up and felt noticeably stronger than before adjustment. Placebo effect, possibly. But I noticed right away that the exhaust "pulses," felt with a hand held behind the pipe exit holes, definitely felt stronger and "poppier." Had the same impression of a bit more ummph on the test ride. Again, could just be placebo effect but it really felt, subjectively, quite noticeable.

northern750 · Aug 5, 2009

I am no authority on Commando valve wear as I am new to these (and all British bikes) but a topic of some interest amongst vintage car owners is the question of emmissions regulations requiring the removal of zinc (zddp) from motor oils over the past few years. Flat tappet engines like the Commando need the zinc additive to prevent wear on cam/tappet lobes. This is a non- issue with ohc or roller tappet engines.

It may be worthwhile to check that the specs of the oil you are using is high in zddp; Castrol GTX 20w-50 and Grand Prix 20W-50 has good zddp content as do many 20w-50 grades but many brands don't contain enough of this additive for our old engines...

Derek.

BrianK · Aug 6, 2009

Thanks Derek. I use Redline 20W-50, which is very high in ZDDP. No telling what the PO used, though.

Hortons Norton · Aug 6, 2009

Derek, I think in the States they have removed the zinc from the Castrol GTX? At least that is what they say. No more SG rating. Could be wrong on this.

Valves loosening?

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