ET: Engine (Twin) Engine Intermittent Cutting Out of One Cylinder

[Rob H]

Don't rush off and buy a head, If I remember where the rocker was , Was very dry ?, Does it look like there is enough oil getting there now ?, Maybe the piston is in trouble, Did you have the barrel off when you did the valve job ?, Seems strange that you are happy with the running of it most of the time.
Cheers Bill.

Rocker is wet and moves freely. I had the barrels off and pistons off, front and rear were pretty much identical. no scoring honing marks still present in some areas of the bore, only signs were slight wear to the rear of the piston which is to be expected I guess. It runs at cruising speed but, not perfectly happy with it as it does not feel as if it is running right.

The reason for looking for another head is that I understood that the wear caused by the loose guide was extensive and it was difficult to fix as a special oversize guide had to be used. I also asked the question at the time whether the valve and seat needed to be replaced as I thought the lateral movement would have damaged the seating on both but was told no.

 

[greg brillus]

A replacement head sounds easy, but hideously expensive..........If you could find one. You would be best off giving the head to a well known machinist who is Vincent savvy, like Maughan's and they could true up the hole and make a special over-sized guide for it. I have done this many times and usually works well, provided the lock ring thread is not damaged badly. The valve seats are extremely tough, so damage is unlikely but would generally clean up with a fresh cut so long as the seats aren't too deeply recessed in the head. Good luck...............Greg.

 

[Bill Thomas]

I understand your worry, I worry over everything, But the lower guide does not have to do much, As has been said, It will run without it !.
The fact that you are not wetting plugs, To me is good.
It's not often I come home from a Vin' ride and say that was perfect.
There are so many things that can upset a Vin'.
I have never done a leak down test, Davidd is always talking about it, But in your case, It might be a good idea
I would try and do some miles and see if it gets better, After all, It's just been in bits for a big job.
Squirt a bit of oil on the inlet manifold joints, To see if it's sucking air ?.
Good Luck, Bill.

 

[oexing]

I would better not do too many miles with an obvious leak down that is even felt by only kicking. A badly sealing exhaust valve would get severe burns and the seat ring as well in the short run. The leak down test is done with aero engines at each annual - for a reason. When a poor cylinder is found they do a flight test of max. one hour and do another test. When OK it was some dirt on seat or valve, otherwise off with the cylinder and head for close inspection , it will NOT heal by itself. In case somebody has been at your engine recently he must have done a poor job, not checking ALL components for correct fits.

Vic

 

[Rob H]

A replacement head sounds easy, but hideously expensive..........If you could find one. You would be best off giving the head to a well known machinist who is Vincent savvy, like Maughan's and they could true up the hole and make a special over-sized guide for it. I have done this many times and usually works well, provided the lock ring thread is not damaged badly. The valve seats are extremely tough, so damage is unlikely but would generally clean up with a fresh cut so long as the seats aren't too deeply recessed in the head. Good luck...............Greg.

The head did go to well known vincent savvy machinist and was told the valve guide had to be made so big it was just only secured by the lock ring. I will do a compression test on both cylinders and a leak down test if I can get the adapter for the plug and will post later. I will not be using the bike until the issue is sorted in case of even more damage

 

[ossie]

Does it chime in on both cylinders if you close the relevent air lever? If so,it must be fuel and not ignition.

MINE HAS NEVER HAD AIR LEVERS JUST FLOOD IT AND GO.

 

[Comet Rider]

Rob,
Where are you?

I can lend you a leakdown tester if you want?

Neil

 

[Rob H]

Rob,
Where are you?

I can lend you a leakdown tester if you want?

Neil

Thanks but you are probably a fair distance away as I live up in Newcastle / Tyne. I had a look on the internet, looks like you can buy a test kit for about £16.00 so will do that unless you live close by that is!

 

[Rob H]

Ok here's an update. Got a leak down tester off ebay, not a bad piece of kit for the price which was only about £16.00 inc P&P, from China but still how can they make, ship and have profit is amazing.

Anyway tried on the front cylinder no tell tale signs of hissing leakage rate at around 10% on the gauge. Tried on the rear cylinder piston tdc and both valves slackened off and to be honest did not need a gauge or the test kit, probably could have done it by just connecting an air line.

Loud hissing noise coming from the exhaust and can actually feel the air coming out so that's about it for the moment until I get the head off, diagnosis exhaust valve repair not working and passing air

 

[chankly bore]

Amongst all the other things to check, some piston crowns have too little clearance in the valve pockets. They need widening a freep. Check the valves for bending, of course.