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ET: Engine (Twin) Fogging for Mosquitos; Valve Guide Issues and Solutions


Cyborg

Well Known and Active Website User
VOC Member
I’ll be dropping some stuff off at his place sometime in the not too distant future, so will ask if I can take a photo or two.
 

Tracey Tilley

Well Known and Active Website User
VOC Member
I am going to add my story here. After investigating an oil leak on the way home from the Annual Rally, turns out the Comet has exactly the same problem.
Seeing as Chris just did this on the Rapide, we thought it would be relatively straight forward, ha ! wrong.
This Comet head has had a hard life. How was this bike even running? One of the locking rings was glued in, the other disintegrated, the valves are toast.
The work needs an engineer, new guides, valves, re-cut the seats etc.
Trouble is, there is nobody that can do the job and get the head back in time for me to ride it before Summer's over. Unbelievable.
{ Wouldn't it be great if a rich person/company sponsored a Vincent apprentice scheme to get young or established engineers learning the speciality, knowing they had customers lined up waiting ? Perhaps it would create an interest in the Marque amongst young people? }
Anyway, Chris is going to do it himself. The oversize guide is 566", and I can order everything he needs.
Buying a valve cutter, learning how to use it and getting that angle right should be fun.
Photos of the metal flying around in the head, the damage and the valve which looks like it's been used for golf.
 

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peter holmes

Well Known and Active Website User
VOC Member
I agree, things are getting very difficult on the Vincent front, there are plenty of cosmetic restorers around, we are probably spoilt for choice, but skilled Vincent engineers are quite a different story, very thin on the ground, and as for hoping to get a cylinder head rebuild done before the end of the summer, well my first question would be what summer were you thinking of.
Tracey, did your bike come from a known source or an auction house or dealer, you see so many bikes that purportedly have been rebuilt by a respected Vincent engineer that no one has actually heard of, it is all a bit risky when Comets are changing hands for £20k+
 
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timetraveller

Well Known and Active Website User
VOC Member
Hi Tracy, sorry to read of your troubles. The thing is you will keep riding it! Before you get a valve seat cutter find out what type of valve seats you have. If the originals have been replaced with lead free seats at some stage then these are much harder than the originals and some of the seat cutters will not touch them. I use a purpose designed grind stone, 45 on one side and 30 on the other. One of the Sussex section chaps tells me that the correct, expensive cutter will work on the hard seats but check it out before you spend your money.
 

nortonpower

Website User
Non-VOC Member
It seems that some of you have long delays on your engine rebuilds. If anyone needs mechanical assistance on his engine, my well equipped workshop and I could get you on the road again quickly. Just contact me.
cheers, Hartmut
 

MartynG

Well Known and Active Website User
VOC Member
I am going to add my story here. After investigating an oil leak on the way home from the Annual Rally, turns out the Comet has exactly the same problem.
Seeing as Chris just did this on the Rapide, we thought it would be relatively straight forward, ha ! wrong.
This Comet head has had a hard life. How was this bike even running? One of the locking rings was glued in, the other disintegrated, the valves are toast.
The work needs an engineer, new guides, valves, re-cut the seats etc.
Trouble is, there is nobody that can do the job and get the head back in time for me to ride it before Summer's over. Unbelievable.
{ Wouldn't it be great if a rich person/company sponsored a Vincent apprentice scheme to get young or established engineers learning the speciality, knowing they had customers lined up waiting ? Perhaps it would create an interest in the Marque amongst young people? }
Anyway, Chris is going to do it himself. The oversize guide is 566", and I can order everything he needs.
Buying a valve cutter, learning how to use it and getting that angle right should be fun.
Photos of the metal flying around in the head, the damage and the valve which looks like it's been used for golf.
I found the attached in a 1983 magazine at the back of my bookcase. It may have some information of interest. It describes how (back then) Maughan's did the job.
 

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ClassicBiker

Well Known and Active Website User
VOC Member
I read Martyn's attachment and it got me thinking. So I started to make my own steady bush that will locate on the upper valve guide seat area. As I am going to ream the hole for front exhaust lower guide in the head to clean up that hole, I was thinking of making my guide bush with interchangeable bushes at the very top to accommodate the different size shanks of the reamers I will be using rather than make two steady bushes.
Which then lead me to thinking about cutting the valves seats prior to lapping them in. Which leads to the question which cutter sizes? I believe from searching through threads here the angle I need is 30 degrees as they are the original seats. I was thinking on purchasing one or two of these cutters https://www.cylinderheadsupply.com/cu616.html but wasn't sure of the size. I was worried that the inserts might contact the lip of the cylinder head. Has anyone used this type of cutter or similar?
Slowly and cautiously moving forward.

Steven
 

Cyborg

Well Known and Active Website User
VOC Member
I have used them and sometimes you can get some chatter. Personally I prefer stones, but there are folks out there that think I’m nuts and they prefer Neway. Whatever you are used to I suppose. Only thing with stones, small drivers seem to be extremely uncommon, at least around here, so end up using automotive equipment. Not a problem, just a little unwieldy for smaller delicate heads.
 

Kiwi_Tim

Active Website User
VOC Member
I've likewise just had issues with loose inlet guides giving me a smokescreen. To compound the problem it turned out one of the upper guides footing wasnt parallel to the lower guide. Presumably has never been so.
Luckily Alan at "Harris Performance" managed to sort it out harrisperformancenz.co.nz and I hope to have it ready for the NZ riders rally coming up very soon.
 

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timetraveller

Well Known and Active Website User
VOC Member
It seems that this fault is occurring more frequently as the bikes get older. Some of you will be aware that when Chris Tilley had this problem I was able to provide him with a drawing of a way to get round this and prevent it happening. Chris managed to get a local machinist to make the parts. I got a price for making ten of these and it worked out at £45 each. These would be CNCd and there is a lot of setting up time which means that it is expensive to make small numbers. I am contemplating getting twenty made this autumn which would have a recess for the oil seal built in. As far as I can tell I can get away with one size which would work with both inlet and exhaust valves. If the valve guide has also been destroyed than a new one of those would also be required but the proposed gadgets will work even if the thread had gone. They would be made of 7075 aluminium alloy which has similar strength to mild steel. If I have to fund all this myself then I will get ten only made as I don't want hundreds of pounds sitting on the shelf for years. It seems to me that a case could be made for several sections or repairers holding some of these in order to do rapid repairs. If anyone out there is prepared to hold a few of these to help out local riders then please contact me at enw07@btinternet.com. The more that are made in one batch then the cheaper they will be.
 

MartynG

Well Known and Active Website User
VOC Member
Norman,

Just to be clear. exactly what are you talking about being made?

Martyn
 

timetraveller

Well Known and Active Website User
VOC Member
It is a tube with a slot in the side to allow the rocker to pass. It is intended to be tight push fit in the cylindrical hole below the upper valve guide. On the top is a part flange which fits into the semi circular cut out for the rocker tunnel to prevent it rotating. At the bottom there is an extrusion which fits on to the top of the flange on the valve guide. If the lock ring is still in good order then this extrusion can be machined off and the gadget will sit on top of the lock ring, I think that I published a drawing of the item earlier on this thread but will try to attach a photo.
View attachment 29354H]
This was an earlier steel version, designed for a local Comet owner and it worked for years. It sat on top of the lock ring but the new design will not require a lock ring to be used. It is black coloured from years of use in the cylinder head
 

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MartynG

Well Known and Active Website User
VOC Member
Thanks Norman,

And here was me thinking it was going to be a steady bushing to ensure correct reaming and positioning for the valve guides.

M
 

timetraveller

Well Known and Active Website User
VOC Member
No Martyn, that is another thing all together. I do that by putting in the top guide and then holding it in place with a tube held down by the valve spring cap. If I do not have access to a stepped mandrel for the reamer I sacrifice a top guide by opening up the central hole in it. The other gadget is intended to overcome a problem which seems to becoming more frequent as the bikes get older. That is the lower valve guide becoming loose, which can only happen if the lock ring somehow fails, The valve guide then becomes loose and makes a mess of the hole it is supposed to fit in in the cylinder head casting. In my own case there were no symptoms I had noticed. I took the bike down to do a different job and found no lower front exhaust guide and the lock ring in three pieces up with the valve spring. No! I don't know how it could do that either. In the case of both of the Tilley's bikes they noticed excessive smoke from the exhaust, hence the title of this thread. The idea of my gadget is that if the hole for the lower guide is worn then one has to make a new oversized guide, The problem then is if the thread for the lock ring has been destroyed, There are people who are clever enough to weld up the hole and then re-machine a thread in there and make a new hole for the lower guide itself. They are rare specialists and I personally do not know any. My gadget is a simple mans approach to the problem and seems to work well enough by lasting for years. None has ever caused further trouble yet.
 

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