Detonation damage?

[Truckedup]

The damage you see here....The engine is a 80's Moto Guzzi V twin bike engine, note the Heron head design...An elderly rider that may have been lugging the engine,...And many air cooled bike engines don't tolerate lugging but usually a piston seizes or preignition blows a hole in it......On this engine type it's not unheard of to drop an exhaust valve but some claim it's just inferior valves.....The rider has nothing to say about any funny noises before it lost power

[Truckedup]

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[mag2555]

Sorry , but I don't by the low speed lugging creating failures like here for the most part.
I think the valve was just ready to give up the Sprit!
It also looks like the piston may have failed first and sections of it jaming the Exh valve may have been what failed the Exh valve?
If air cooled motor can live under high speed high load conditions with out over heating , then what's the issue wuth low speed lugging?
How was the motors tune?
If it was at max temp and running lean at low speed with minimum octant fuel then I could see a issue in the making!

[Truckedup]

Sorry , but I don't by the low speed lugging creating failures like here for the most part.
I think the valve was just ready to give up the Sprit!
It also looks like the piston may have failed first and sections of it jaming the Exh valve may have been what failed the Exh valve?
If air cooled motor can live under high speed high load conditions with out over heating , then what's the issue wuth low speed lugging?
How was the motors tune?
If it was at max temp and running lean at low speed with minimum octant fuel then I could see a issue in the making!

Lugging an air cooled engine often results in detonation especially on older designs that are marginal on modern pump gas...Without the ability to deal with fast heat rise like on a liquid cooled engine, it all goes to shit very quickly..The engine is stock, state of tune is about one HP per cubic inch,7000 rpm maximum power, typical for a two valve pushrod bike engine .I'm not familiar with the Heron head's octane requirements.....I have seen the results of detonation damge from lugging many times but not like this exactly.....But I'm not saying this is detonation, just asking...

[4vpc]

Define 'Dropped a valve' as it's about as accurate as 'engine broken'.
You'll have your work cut out trying to do an accurate PM on that one given the damage left by the valve head.

[Truckedup]

Define 'Dropped a valve' as it's about as accurate as 'engine broken'.
You'll have your work cut out trying to do an accurate PM on that one given the damage left by the valve head.

Yes, so perhaps my question should be " can detonation alone cause an exhaust valve failure ?"

[Walter R. Malik]

IF the excess heat causes the stem to stick in the guide ... it sure can.

[Truckedup]

IF the excess heat causes the stem to stick in the guide ... it sure can.

I'm very familiar with severe detonation on the vintage Triumphs....It almost always causes a four corner piston seizure..In addition the piston pin can seize..This usually happens before the piston lands break.But this Guzzi engine may have different results, like a stuck valve.....Lugging for air cooled bike engines is any time you open the throttle and speed does not increase other than flat out in high gear...

[PackardV8]

Today's engines live live long and prosper with low RPM and high compression because they have ECMs/EFI. The old bikes, with their stone-age carb/distributor, survival was/is marginal even when tuned and ridden correctly. The worst I ever owned as a '66 BSA Lightning; fastest thing around until it made that noise. Years after the Beezer was junked after the third dropped exhaust valve, someone claimed the problem was an incorrectly profiled distributor point cam which caused random timing and overheating.

When the Beezer dropped a valve head, it was obvious the stem had stuck in the guide and been hammered off by the piston. As mentioned, from those photos, difficult to state definitively. An examination of where the stem and head parted company would give more info.

Does anyone else think there's enough oil evidence to have caused detonation?

[user-23911]

You'll see more once you get the piston out.

[4vpc]

And the valve stem...

[Truckedup]

Today's engines live live long and prosper with low RPM and high compression because they have ECMs/EFI. The old bikes, with their stone-age carb/distributor, survival was/is marginal even when tuned and ridden correctly. The worst I ever owned as a '66 BSA Lightning; fastest thing around until it made that noise. Years after the Beezer was junked after the third dropped exhaust valve, someone claimed the problem was an incorrectly profiled distributor point cam which caused random timing and overheating.

When the Beezer dropped a valve head, it was obvious the stem had stuck in the guide and been hammered off by the piston. As mentioned, from those photos, difficult to state definitively. An examination of where the stem and head parted company would give more info.

Does anyone else think there's enough oil evidence to have caused detonation?

Well, A Guzzi shop owner just told me the V65' engine shown above that are no longer in production have poor quality valves and too much valve spring pressure....And he said the Heron head isn't detonation prone...

The BSA's of that era were extremely poor built quality do to many labor and management problems. The points cam was a wrong profile and allowed a "phantom spark" causing preigntion and or detonation....Triumph 500-650's in their day were not fragile engines could be flogged without worry....but like you say the rider did need to pay attention to ignition timing if he rode hard...Today with 93 octane the rider needs to pay more attention because they don't tolerate heavy throttle detonation....Actually ,all the older air cooled bikes can hole a piston in a heartbeat ...

[HeinzE]

truckedup,

This looks like a Moto Guzzi V50 engine, yes? I worked for years in a Guzzi/Norton/Ducati/Ossa/Hodaka dealership. The V50 came out after I quit the dealership and opened my own shop, but I did see a couple and even converted one to 750...and no, don't even think about going there...one of the most nightmarish jobs I ever undertook. Anyway, my experience with these engines, albeit limited, was that they were a fairly nice runner with OK performance and good reliability. You said that the previous owner was "elderly". Do you know if the bike sat for any period of time? I've had my share of old bikes in my shop that had been stored for long periods and it was not unusual to see rust on the valve stems, especially if they had been stored outside or under only a tarp or car port. I agree with the earlier post that you'll know more once you get the valve stem out of the head. Take a close look for any signs of rust pitting or corrosion. Check the other valves as well. It wouldn't take much of a rust patch or corrosion line to block the migration of oil down the guide, and if that were in fact to happen, the valve would probably stick in the guide in fairly short order with the predictable results. But on a lighter note...once you get this repaired and back on the road I think you are in for a bit of a treat and surprise. While not a road rocket by any means, the V50 was a sweet, smooth runner with excellent handling and fine brakes. Good luck.

Karl Engellenner

[HeinzE]

truckedup,

Sorry, I missed the fact that this is a V65. But no matter. Everything I said about the V50 is even more true of the V65.

Karl Engellenner

[naukkis79]

Exhaust valve seat seems to be very wide. Usually that means that valve has sinked and valve clearance has lost. As valve is operated without enough clearance it will overheat and eventually fail.

With air cooled engines is crucial to check and increase exhaust valve clearances regularly.

And in combustion chamber I don't see any signs of detonation.