Guzzi T3 running very hot on r/h cylinder almost certainly not carb or ignition?

[falcone]

A friend has bought a T3.

Not run for some time but purportedly rebuilt by a well known professional. He worked abroad and didn't have time to look at it 'til now.

It starts easily and runs fine to begin with but the right cyl is getting extremely hot, the right header pipe glows deep red hot at any sustained rpm of 2000 and upwards and heat rises in a column above the RH rocker cover, so burning and dissipating greater heat than normal.

The L/H cylinder runs fine.

Clearly the rh cyl is retaining far too much heat in the burn stroke for some reason, so what could cause this?

 a) The exhaust valve might not be opening fully, thus not fully exhausting, retaining heat on its stroke? What might cause such a symptom?

 b) if the push rods have been inadvertently swapped/not checked at rebuild for length/bent, the exhaust valve might not be fully opening, thus not fully exhausting, thus causing a heat build up?

The burn at the plugs is pretty good, they are a light brown, not grey, so the burn is not lean or too lean, and we have tried with 2 separate sets of plugs.

As the engine idles well, pulls well from low revs upwards and we’ve checked ignition and reasonable carburation tests, these 2 factors seem not to be the cause of the overheating, so rapidly running out of logical ideas, leads to an internal  engine occurrence/problem, which is tending to lead me to the exhaust valve area and possibly the pushrod or the valve spring.

Any thoughts? All most welcome.

Neither of us are experienced enough to be honest.

[Gliderjohn]

Have the valve clearances been checked?
GliderJohn

[guzzisteve]

I would do a compression & leakdown test after a proper tune up. Have you ridden it on a road? or just in shop?

[falcone]

Yes we aren't bright but we know that much :-( They are all fine :-(

[falcone]

Thanks for your message. We have only run in the shop and not on the road. A compresssion test is on the cards. Dave

[pete roper]

Double check the ignition timing. Sounds like the spark on the offending side is horribly retarded.

[rodekyll]

^^^ this, first.  Also check that the advance mechanism is working.  Otherwise, assuming the valves are in adjustment and the mixture is reasonable, the compression/leakdown test is in order.

[twowings]

Are you getting equal pulses from the exhaust system? Perhaps a blocked muffler?

[falcone]

Many thanks for the replies.

Next time I go I will check out various things:

Two wings - Pulses will check, blocked mufflers? both are brand new but you never know? Thank you.

Pete Roper - Have checked the ignition timing several times and 'seems' to be spot on but worth doing again thank you?

Rodekyll - interesting is made up of two units, came without advance mechanism etc and a second hand one put on,  so you never know? Will look again, thank you.

Glider john - the valve clearances have been checked but again will do again, thank you.

As 'seems' not to be carbs or ignition I suspect we will have to take the heads off again and look at the valves?

Again many thanks.

[dxhall]

If checking the obvious doesn't reveal the problem, I agree that the head should come off.  If I encountered this and the jetting and timing were right, the thing I would expect is an exhaust valve problem - something keeping the valve from making full contact with the seat. If the seat or valve head were bad, and allowing exhaust gasses to escape, the valve clearance would still appear to be correct.

I'd take the head off and lap the valves.  That will show if you have proper valve/seat contact. 

[falcone]

(dxhall) Thanks for that I'm sure we will end up doing that very thing :-)

[Chuck in Indiana]

(dxhall) Thanks for that I'm sure we will end up doing that very thing :-)

A leak down test will tell that in a heart beat. My list when trouble shooting is look at the plugs. You've done that, and say they look normal. Adjust the valves. Leak down test. That will tell you about everything about an engine's internal condition except for loose valves in the guides. Once it passes all that, *then* start looking at ignition, carburation, etc.

[Antietam Classic Cycle]

I just wonder during the rebuild if the pushrods weren't moved from one valve to another?  Probably the last thing to look for from the other stuff listed here.

Pushrods are all the same length (at least they are from the factory), so unless one is bent, they aren't likely at fault.

[Sheepdog]

Sounds like an intake leak.

[dxhall]

Agree that a leakdown test would show the valve problem, but most guys don't have a leakdown tester.  When I was racing, I'd do a leakdown test before the race, and again when I got back to the shop the next week.  I'd start at 3% or so Saturday morning, and see 20% when I got home.  Depressing.  Used to do a lot of valve lapping.

[Antietam Classic Cycle]

wouldn't they wear out at different shapes and lengths?  And then placed back in the wrong guide after rebuild affect valve lift?

They should all "wear" the same. In reality, I've never seen one wear any differently than the others. Any proper rebuild would have included replacement lifters, so the pushrod wouldn't be going back together with the "matching" part anyway. Any effect on the valve lift would be minuscule and unlikely to cause an issue.

[th_01]

I'd do the simplest things first.

Adjust the exhaust valve on the hot side a little loose and see if that has any effect.

Maybe Charlie can shake the cobwebs out of my brain here.   Air leak around the exhaust gasket or intake manifolds could also cause an issue. 

Good luck
Let us now what you find

[guzzisteve]

I would take it out and flog the hell out of it on a ride then see how it is.

[rodekyll]

What we're looking for is an imbalance between the pots.  There aren't a lot of things that affect just one side, and it appears that barring the really weird problems (wrong heat range spark plug in one side only, completely goofed up plug gap, or a burned piston, all the bases have been covered.  What I'd do is give a friend $20 and a half-rack to go back over my work and find it.  The OP is too convinced everything is right.  A fresh set of skeptical eyes is needed.


I'd think that one muffler plugged would affect engine performance, but I'd think (due to the crossover) that it would not overheat one side.  If it did overheat it would be both sides.  If both sides are restricted then the bike wouldn't run.