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

Kiwi_Tim

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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

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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.
 

timetraveller

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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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Martyn Goodwin

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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

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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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