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Broken cylinder spigot

Submitted by peter_brown1 on Sat, 06/11/2021
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Heavy Twins

My 99 has a broken spigot, about 1/3 missing, bores are very good nick at 68.25. Seen a lot of comments about leaving it, machining them off and use or not use filler rings in the head. Can’t find any info about machining them off then counterboring into the barrel 1/8” deep then fitting steel rings to create new spigots. At only 1/8” deep the top ring won’t meet them. Is this a good idea?

cheers

Pete

Submitted by robert_tuck on Sat, 06/11/2021

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Leaving the broken spigot in use  is probably not good as it may continue to break up. I think I would try it without the rings  as they can have issues.  A slight reduction in compression is not a bad idea  as the engine will have an easier time.

Submitted by philip_hannam1 on Sat, 06/11/2021

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I had the same problem with my first 99 engine after it was rebored to +60".  I just sawed the spigots off both sides and then ground the remaining top surface smooth. The loss of the spigots made  no discerable difference to the engine performance when I used a Hallite head gasket. 

One of the big name suppliers was, until recently, selling cylinder head packing rings for the 88, 99 and early 650 engines. Also around, at the same time, was an oversize head gasket that filled in the gap left by the missing metal.

Thanks for commenting, what issues do you know of for rings let into the barrel, have heard of some with the ali filler rings for the head. Thanks

Submitted by david_cooper on Sat, 06/11/2021

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Later engines had no spigots. So removing them is not really a design change. Adding home made "improvements" is a change. It's OK for a factory to change the design because they can test to destruction if they want to, but the private owner can't do that (unless he's very rich). 

And rings would surely bring in all sorts of tolerance issues?

Will probably just take the spigots off, and maybe use the alloy head rings from RGM. Not sure what you mean by tolerance issues, I can machine to better than 0.001”?

Submitted by david_cooper on Sun, 07/11/2021

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When the head is pulled down onto its gasket, will it touch the ring or not? Will the gasket hold it up so the ring is loose, or will the ring hold the faces too far apart? The rings have been known to escape and end up inside the combustion chamber...and then you risk damage to pistons and valves. The gasket goes outside the spigot so it goes outside the filler rings. So it's not even as simple as making sure their thickness is the same as the depth of the recess in the head.  There's been previous correspondence here about them.

Sorry ref the tolerance thing thought you meant my ‘homemade’ jobs. You can buy a gasket for spigotless barrels that would help trap the filler ring, yes i too am concerned about the head filler rings falling out as little supporting them. If i did insert the barrels i plan to make the recess in the barrels larger than the spigots and have a step on the insert flush with joint face.  will probably follow general wisdom of just mill them off and live with the head gap

Submitted by philip_hannam1 on Sun, 07/11/2021

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Norvil have a range of cylinder head gap filler rings on sale. I believe they are still made from Aluminium. I purchased a set for my Atlas many years ago and they gave no problems being squashed between the inner lip of the cylinder head and barrel top. As the inner lip was slightly convex this also helped to stop any movement.

These are the Norvil part numbers....

750 engine - 25494

650 - 990613

500 - 61174 (this is a special set to allow larger heads to be fitted)

 


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