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

timetraveller

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VOC Member
Steven, if you search these pages back a few weeks you will see that Chris Tilley from South Wales had a similar problem. I have also had the same problem as had one of my local chums. The solution was that I designed a part which fits between the top of the lower guide and the bottom of the top guide and this prevents the lower valve guide from ever starting to work itself loose. I sent drawings to Chris and he got a local machinist to make two very nice items which also allowed him to use the oil seal on top of the lower guide. I am prepared to get a batch of these made if the interest is there and although the two I had made originally were made of steel I would probably use 7075 aluminium alloy for these as it has proved its worth and strength in the aluminium John Emmanuel steering heads I have had made. It will have to be a batch. The reason is that the chaps who do the CNC work for me do not really want to make less than ten off of any item. When I try to get one (or four offs) I run into trouble with people fitting the work in. E.G. I have been waiting eight weeks for some minor stainless steel parts to be made to fit an alternator kit to an open 'D'. Have a look at the Chris Tilley correspondence, which does include a drawing so you can make your own if you have the skills, and then let us see whether there is enough interest to make it possible to get a batch made.
 

clevtrev

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VOC Member
Well personal circumstance didn't allow me to tear into the motor and find the cause of the problem. So I have resurrected this thread to bring everyone up to date. In another thread I mentioned I had purchased the new extended rockers to install when I figured out what was going on with the sudden smoking. Well over the Easter weekend I pulled the heads. Bur first I started the Shadow to see if by some miracle it had healed itself. Not. So I made a by pass on the oil line to the heads and rockers. That stopped the smoking and lead me to believe that the cause was an worn guide allowing excess oil into the cylinder and/or exhaust causing the smoking. When I removed the muffler/silencer I heard a rattle. I thought it was the baffle loose inside. Until a little something fell out. At first glance it appeared to be a lump of carbon. Closer inspection revealed it was metal. In fact it had a curve to it. I looked up the inlets and exhausts of both heads and could see the top of all the valve guides, except the front exhaust. I could see the valve guide retainers, except the front exhaust. This did not bode well. With both heads off, I removed the valves from the front head. The lower guide is completely gone. The little bit of shrapnel I found in the exhaust is all that remains. The threads for the guide retainer are completely fretted away, only the retainer remains.
Now I have to decide whether to repair the head by the methods I have seen on the forum of making an insert to retain the lower guide or purchase a new head. But first I must determine if the hole for the lower guide has been worn excessively or not. Does anyone know the standard o.d. of a lower guide?
Of interest the upper guide appears to have been sufficient to keep the valve aligned as there doesn't appear to be any damage to the valve or head in the seat area.
Steven
It would not have been the upper guide controlling the valve, it was the rocker arm, and if you look in the combustion chamber you will see where the head of the valve has been seating, you will notice that it has been seating more on the same side as the lot in the rocker arm.
The lower guide diameter was 9/16". Exhaust that, Inlet is 1/2".
 

chankly bore

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Non-VOC Member
Exhaust guide standard o.d. is .563", lockring thread is 7/8"x 20 t.p.i. Whitworth form. Maughans can probably reclaim it.
 

ClassicBiker

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VOC Member
TT, that is the thread and repair I was referring too. While I feel confident I could make the item myself, why re-invent wheel? If you were not considering having a batch made, I would under take making myself a set. Now that Clevtrev has kindly supplied the o.d.s (Thank you Clevtrev) I will get my telescoping gauges out and see if the bore of the missing valve guide is in any condition to take a standard or over sized guide, or if there are other issues as a result of the guide calling it quits.
Chankly Bore popped up while I was typing this.
I had not considered them. They (Maughans ) would definitely be less than a new head or two. I will have to see if the guide bore or valve seat is severely damaged. After reading what Clevtrev says about the valve seating to one side based on the slot in the rocker arm.
Thanks for the input and suggestions. I will update as I find out more.
Steven
 

timetraveller

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VOC Member
I got a price this morning from the CNC chaps. £45 each for ten off and a bit cheaper for 20 off. This is more than I expected so if any of the engineers in the Club feel like making a batch at a better price than that please talk to me on enw07@btinternet.com . Over to you guys.
 

ClassicBiker

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VOC Member
Just rang Maughans. They can reclaim the threads and do no-lead valve seats but they are so loaded up with work they are not currently taking any more on. Their suggestion was to call Conways and see if they would take it on. Thoughts?
Steven
 

Bill Thomas

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VOC Member
Have the threads been damaged Steven ?.
The Spares Company sold oversize lower guides, Last time I looked, Some years ago ?.
Good luck, Bill.
 

ClassicBiker

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VOC Member
Hi Bill, unfortunately the threads are completely gone. If it weren't for the fact that I know there should be threads there and the lock ring was floating about, you couldn't convince that there were ever threads there.:eek:
Steven
 

Bill Thomas

Well Known and Active Forum User
VOC Member
If you could sort out an oversize lower guide, I would have thought someone near you could put a bigger thread and make you a special thread ring ?, Just a thought. Cheers Bill.
 

roy the mechanic

Well Known and Active Forum User
VOC Member
Steven, first off you do not need no-lead valve seats. The originals in my rap have done the best part of 300000 miles and the tappets rarely need adjustments . I have visited Conways , they have a comprehensive machine shop. The only thing that would concern me is shipping parts for many thousands of miles, not only will they get there, but will they get back, having paid for the work. Whatever you decide, be lucky. Roy.
 
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