E: Engine Cylinder Head Crack

LoneStar

Well Known and Active Forum User
VOC Member
Hello all,

The rear cylinder head on my Series C Black Shadow has developed a crack at the exhaust valve guide bore. The bore is also belled out, measuring .566 x .585" at the inner end. This was likely caused by the piston having broken apart, with the separated crown hitting and bending the valve.

What's the best way to deal with this unpleasantness?

Thanks,

Dave

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brian gains

Well Known and Active Forum User
VOC Member
are head castings that porous not unusual , I don' recall mine having that appearance or is that just a consequence of the spontaneous porting job ?.

jobs like that I split between dedicated welders and dedicated machinest and if you're lucky they talk to each other.

Or, Alp Racing Design. No affiliation etc etc but the fellah seems to have the gift with skills.
 
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Vincent Brake

Well Known and Active Forum User
VOC Member
Or leave it be and put in a full valve guide all the way up. Over forks and closed up by the top valve guide.

May be only solder a bit on outside.

Like the heads of Ernst Hegeler.

Easy repair.

Welding is messing up a lot there....

Or godo when you want to trash down the roads (riding i mean)

Not to much interf fit.
Say 2-3 thou.

A good bronze.
Alu Fe bronze?
Ampco 45?

Much wisdom send to you
 

roy the mechanic

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VOC Member
Looking at the picture, it has been "mended" before. If it was mine, by the time it has been welded, machined back, one-off guide made and fitted, I would just buy a new head and get most of the cost back from evil bay.
 

Vincent Brake

Well Known and Active Forum User
VOC Member
Looking at the picture, it has been "mended" before. If it was mine, by the time it has been welded, machined back, one-off guide made and fitted, I would just buy a new head and get most of the cost back from evil bay.
Haha Roy,
Was it yours that i bought.
It was advertised correctly though
Presse Papier.

Cheers

But i guess your right
 

LoneStar

Well Known and Active Forum User
VOC Member
Thanks for the ideas, everyone. I consulted with Glenn Bewley - the head can be repaired, but the cost approaches that of a new one. So, I'm leaning towards replacing it.

I hadn't considered listing the current one on Ebay, but it does seem to be a mainstream idea; quite a few Vincent parts there are clearly replaced rejects. No harm if disclosed, I guess.

VB - I'm not understanding your idea of a full-length guide. How does the rocker fork reach the valve stem? Any photos of this setup?

Cheers,

Dave
 

davidd

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VOC Member
VB - I'm not understanding your idea of a full-length guide. How does the rocker fork reach the valve stem? Any photos of this setup?

This is the set-up:

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I think think that this would definitely repair it, but it seems like some serious overkill. I would be inclined to machine the hole round and fit an oversize guide.

Alp has done this repair because one of the heads had a broken a valve and cracked the guide:

Head Repair  (9).jpg


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Head Repair  (13).jpg


Head Repair  (11).jpg


David
 
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