Is it possible the cam has slipped in the pinion.........
Exhaust reversion
- Thread starter charles d cannon jr
- Start date
Is the inlet valve in question gas tight when tested for leakage at seat? In the 1970s, I saw lots of mixture blowback on little Hondas with worn out valves. A valve grind generally cured this.
Also, are these club springs or RD race springs? Some years ago John Mcdougall had a problem with a Customer's bike not performing well a few thousand miles after he had rebuilt the motor. He tested the spring pressure and found it had dropped to about one third of the installed pressure, in a word, knackered.
He then installed RD valve springs and the bike instantly had full power, about twenty MPH greater top speed, as I recall. RD springs now get fitted to every engine he builds. I
think Dan Smith was the first to contact RD about making up valve springs for Vincents and probably the first to use them.
Glen
Also, are these club springs or RD race springs? Some years ago John Mcdougall had a problem with a Customer's bike not performing well a few thousand miles after he had rebuilt the motor. He tested the spring pressure and found it had dropped to about one third of the installed pressure, in a word, knackered.
He then installed RD valve springs and the bike instantly had full power, about twenty MPH greater top speed, as I recall. RD springs now get fitted to every engine he builds. I
think Dan Smith was the first to contact RD about making up valve springs for Vincents and probably the first to use them.
Glen
I use RD springs, but I am not sure that it is a simple replacement. I use their titanium collar and their keepers which means that you have to turn the valve stem down for their keepers. I believe they supply the Goldstar spring for Vincents. Because you are locating new keepers on the valve stem and using all the stem because the spring is a little longer, you may have to raise the valve caps for clearance and you will definitely have to adjust for your desired cam pressure.
But Glen is correct that the springs can go wobbly. I had an engine that was not performing well and when I took the valve caps off I could push the springs open easily by hand.
For the hot-rodders, RD does sell beehive springs even though they are not listed on their website.
http://www.rdvalvespring.com/
David
But Glen is correct that the springs can go wobbly. I had an engine that was not performing well and when I took the valve caps off I could push the springs open easily by hand.
For the hot-rodders, RD does sell beehive springs even though they are not listed on their website.
http://www.rdvalvespring.com/
David
David, I used the Terry Prince RD kit and some of Terry's keepers on the Oz Rapide. I was there when John Mcdougall fitted the new valves, which were standard issue, tho purchased from Terry. John tests every installed valve setup by giving the stem a big smack on top with a mallet. Occasionally he encounters keepers that do not fit properly. This was one of those intances, a keeper let go and flew out. He substituted Spares Co. keepers and all has been well for 40,000 miles.
Now that you mention turning down the stems a little, this was the problem, the keepers Terry supplied (probably RD) were a bit too small in radius to fit the stock valve. Rather than turn down the valve stem, changing to standard keepers worked and must have fit in the RD collar ok as well.
Now that you mention turning down the stems a little, this was the problem, the keepers Terry supplied (probably RD) were a bit too small in radius to fit the stock valve. Rather than turn down the valve stem, changing to standard keepers worked and must have fit in the RD collar ok as well.
Regarding my heads, Jim Baltusnik,who sold me the basket case, had had both heads done by Steve Hamel, who has a very good reputation. The heads had not even been used after rebuilding. I've done leak downs and compression checks. There is minimal leak down and I've got 150-155 pounds on each cylinder.
interesting to know thoughts on spring poundage at seat. I just renew my standard springs but last time I had some valves with a smigen of extra lift I went for some Molnar springs and a poundage of (from memory) 120lbs at seat height. I have to look for some specials again soon....
I think that you will find that Terry Prince sells springs which give a standard seat pressure and allows up to half an inch of lift without becoming coil bound. They might be of Jawa origin but that needs to be checked.
Qute right T T, Terry sold me "the springs to go with mk4 cams" When the heads were mounted in the vice with the plughole holder I had to use an 18" lever to make them move! when investigated by my pal who builds w r c motors he was horrified, the seat pressures were 200 lbs, over the nose 340 lbs! We all know that vins suffer with cam/ follower troubles, reckon mine would have lasted 5 minutes like this. We have gone for 85 lbs seat 120 over the nose. Trust no-one, always do your own homework.
If my experience with the springs this man supplies is anything to go by, the wire is of heavier gauge which results in a greater than standard O.D. causing the springs to not fit into the lower guide and sit at an angle, therefore putting an axial load on the valve stem. As you have also found the huge increase in pressure from these springs is trouble waiting to happen. Fortunately I was alerted to the problem by the posts on this forum a few years ago, (May 2007 if you wish to read the full horror story) when “Black Lightning 998” ran his Australian re-built engine to a disastrous end. In the event a check revealed my engine fitted with the same non standard springs, as for the re-built engine, having run very little, no apparent damage had occurred and it only cost me a new set of springs! What a useful resource the forum is, and thanks go to Graham.
Col.
Col.