cylinder weld and powdercoat questions

maylar · Aug 12, 2012

A buddy of mine is repairing his 72 Combat motor and will be doing a bore & hone on the cylinders. He also wants to have them powder coated and we're considering the sequence that makes the most sense. I suggested powder coating first, then machine work - but on inspection of the cylinders we found that they had been repaired with a weld once before and it looks to me like it should be redone. You guys think this needs attention, and can it be done after powder coat?

Thanks

rvich · Aug 12, 2012

If I could afford new barrels, I would probably go that direction. If I couldn't afford new barrels I would probably run it as it is! What ill effect will it have other than holding some extra oil? As for powder coating, I wouldn't powder coat my barrels. I would instead use a product that helps shed the heat. If somebody is going to be welding on that, I would think you might destroy the powder coat.

Russ

kevbo82 · Aug 12, 2012

yeah i don't think powder coating will stand up to much heat either. maybe only 350-400ish?

SteveA · Aug 12, 2012

I bought a set of barrells yesterday...they are powder coated! They are also sleeved for a 920, and have every other fin machined off....

...and where they are sleeved there are no cut outs for conrod clearance in the spigots....

I am sure there is a lot of opinion available, but has any body got any factual experience of barrells like these? in a race bike context , not road.

My first motivation to buy the barrels is to use them in a mock up engine whilst dry building the rest of the bike, its a Rickman frame and I have a lot of fitting and alignment to do and will need an exhaust made around it so a mock up phase is essential. But I will consider using the barrels in a build if I can find out more about their potential.

Steve

Bob Z. · Aug 12, 2012

Was breakage at the cylinder bore base a fairly common problem?

I posted this photo previously of a spare 850 cylinder from a blown up motor.

comnoz · Aug 12, 2012

It is common if they break a rod or piston- or somebody drops them. Jim

Hobot · Aug 12, 2012

Trixie has run her broken out bottom bores for at least 8000 miles now no problemo. If your welded barrels survived runing prior should continue to. Many barrels survive just fine power coated in various colors to boot but its not very tough and does stifle heat dumping so not used on real hot rods holding on to hi fuel burning. Look up GunKote or similar for DIY simple spray on and bake on sight heat and corrosion covering. Its so thin it takes a few coats and will not cover up any surface texture, which is a good thing to me. Touch up is just spray more on and ride off to self bake set it.
http://www.larsontactical.com/id30.html

maylar · Aug 13, 2012

I know the repair is below the ring swept area, but it just feels wrong to have those voids showing through. And they'll no doubt get bigger with an overbore. I'm thinking the weld should be ground out and redone but I can't weld cast iron.

Oddly the bores are std sized.. is it possible they came from the factory like this?

comnoz · Aug 13, 2012

maylar said:
I know the repair is below the ring swept area, but it just feels wrong to have those voids showing through. And they'll no doubt get bigger with an overbore. I'm thinking the weld should be ground out and redone but I can't weld cast iron.

Oddly the bores are std sized.. is it possible they came from the factory like this?

I would doubt they came from the factory that way. To weld the bore the whole cylinder would need to be heated red hot and then after welding, slowly cooled over about 24 hours or you will end up with hard spots in the cast that cannot be bored. It would be cheaper for you [or the factory] to just use a different barrel. It might be a different story if you could weld it yourself and were not paying for the hours required to get it right. Jim

xbacksideslider · Aug 13, 2012

I wouldn't use that part. False economy, it puts the entire engine at risk.

Hobot · Aug 13, 2012

Ugh, it would be better peace of mind as home fades into back ground but not out of thoughts, ugh. We are not young struggling dependents anymore so less desperation repairs to live with like me on P!! with welded back fork slider when barely able to feed myself. Every decent Commando has its blood sweat swearing and tears tale attached.

Onder · Aug 13, 2012

Well put Hobot. A set of used jugs arent that much in the long run.
New ones arent worth it, might as well apply to Maney for his.

Hobot · Aug 13, 2012

I/\'m a bit schizophrenic, they tell us, and a bit poor semi-retired, so on the other hand I can equally rationalize if barrel has been run w/o issue then they're proven ok and not a high stress area anyway, so I'd likely spend on something else instead.
Sorry to confuse the decision - unless new data and history revealed.

Ron L · Aug 14, 2012

What about boring and sleeving the cylinder?

comnoz · Aug 14, 2012

Ron L said:
What about boring and sleeving the cylinder?

If it were an 850 that would work. I have done quite a few.

When you sleeve a 750 barrel it leaves a very weak area just above the bolt flange that is likely to crack. I won't do them any more. Jim

cylinder weld and powdercoat questions

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