E: Engine Cylinder Head Crack

LoneStar

Well Known and Active Forum User
VOC Member
I see. Actually I've made and installed one of these, based on your earlier posts, to replace the ET122 guide lock ring. This in response to the ring having come loose at one point, destroying the threads in the head.

But I don't know if I'd rely on it to hold the guide in place in a loose bore. I think the cracks would have to be welded up before machining a new bore for an oversize guide - unless the guide bore could be made large enough to eliminate them; not sure how deep they go.

All this skilled work is beyond my abilities and equipment, and will cost about what a new head would - so that looks like the better option at this point.

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Bill Thomas

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I think we can worry too much sometimes, I know I do !.
Welding can bring it's own problems,
I have had a small crack between the valve seats, On my L/ning rep',
For more years than I can think,
But it's up to you, Really it's a money thing, I don't have any ! :D .
 

timetraveller

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VOC Member
HI LoneStar' manufacture of these is beyond my capabilities as well. I had a batch CNC machined and they are not intended to hold a loose guide into place. Rather, if the guide has become loose and the hammering has worn both the hole and the thread beyond use then the idea is that an oversized guide should be made, with an interference fit, and held into place by the new gadget. I have designed the new batch so that they will work with both inlet and exhaust guides and allow the use of a seal as well. The single design can be used as is on an exhaust with a ruined thread, on a similar inlet by slightly reducing the diameter of the lower oil seal retaining recess or, if the thread is still useable then the lower part can be turned off so the bottom is flush and it can be used to prevent the guide ever coming loose again. I think there will be a full description with photographs in the next MPH.
 

ClassicBiker

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They aren't that difficult to make if you have a lathe. After I saw timetraveller's post about them in another thread when I discovered my retaining ring had backed out and allowed the guide to self destruct and destroy the threads. The hole for the guide was also a little wallowed out so I turned a reamer guide and selected an over sized reamer to clean it up and made an over sized guide. MartynG posted an article how Maughans does the job. I used that article to figure out how to make the reamer guide. If you use the search and look for valve guide or valve guide repair you should find them.
Steven
 

oexing

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I wonder why there are numerous problems with valve guides on Vincents when you have two guides per valve ?? Poor shrink fits or unsuitable fitting replacement guides by cold bashing them in ?? When the lock ring goes you had obviously loose guides and maybe some seizures on valve stems so high forces on the assembly ! So take care what material you decide to use for guides, chromed stems a good idea as well, but availability . . . .

Vic
 

ClassicBiker

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No I don't think my father installed them incorrectly 40 years ago. Neither he nor I had any issue in forty years, but obviously something went wrong. I do know that the owner previous to my father had some kind of issue as of the three surviving retainers two were UNF threads rather than the original thread. I have no idea what the destroyed thread was as there wasn't enough left to make a determination.
 

LoneStar

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VOC Member
There appear to be diverse causes for guide problems. In my own case, there were two rounds of difficulty:

- The ET122 lock ring had loosened, and wore away the threads in the head as it vibrated. The guide itself wasn't loose. I fixed this by making and installing the alloy spacer unit as described by TT.

- Later, the piston crown separated from the gudgeon pin, striking and bending the exhaust valve. This also forced the entire guide sideways, enlarging the bore and cracking the surrounding alloy. This is the current problem, and due to the cracks I don't think it can be fixed with a simple oversize guide.

The one-piece bronze guide with extended cylinder, as Lintman posts, is a nice solution. I think in all cases, though, one needs an interference fit between the guide and its bore to insure rigidity.

Cheers,

Dave

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