Stuck valve..

[Canuk]

Worked on all the wiring today...Started the car and took it for some new fuel...

The engine ran pretty rough so when I got home I did a compression test...It turns out I have a valve stuck open...

Any ideas or have I got to pull the head...

Feedback would be appreciated...

[Smiffy]

Your sure it's stuck and not burnt out

[Canuk]

I pulled the valve cover and the valve is stuck open...

It was fine last year when [arked up for the winter...

I have 160 PSI on the other 3 cylinders...

[Smiffy]

In either case you really need to remove the head and find out why, bent valve or seized in the guide due to incorrect clearances/fitting.

[Canuk]

It ripped it down today and found an open valve on #2....The head is pretty gummed...I pulled the valve and found the guide and valve tight....I cleaned down but could not get the valve to close,,,Pulled # 3 and found the problem, The brass guide in #2 is loose and had moved its self down...What do you recommend to sort this....any suggestions would be appreciated.

[Vegard]

Either you need to find some oversized guides, or knurl the existing one. That works best with bronze guides. I think that 251ENG talked about oversized guides? Simon?

[Canuk]

The guides are bronze,,,I will remove it and preen it and see how that goes...Should the guides have rubber boots on them...

[36inter]

Please do not waste your time knurling or peening valve guides to fit in the head, the whole system revolves around shifting heat from the combustion chamber and the valves are at the forefront of this, heat goes into the valves which is transferred to the guides, if you peen the guides there is very little of the guide contacting the head therefore there is very little heat transferrence so it all overheats.

You need to bore the guide hole oversize back to clean metal and fit an oversize guide, nice and tight, this will ensure good heat transferrence, not only will the guide not move it will perform as it should.

I will probably open a can of worms now but if you are using stainless valves do not use cast guides, no matter if they are plasma nitrided, the valves that is. This is not a good combination whatever anyone says, I have vast experience with this on my 1930's Norton motorcycle, old style nimonic valves, as in KE965 work fine with cast guides, stainless does not, I can go through a new cast guide and stainless valve set up in less than 50 miles and have done so numerous times despite what the 'experts' tell me.

The valve picks up from the guide and it ends up like a rasp and eats its way through the guide big time.

Your valve rocker geometry is also vitally important, if you have had the head or block skimmed this may have changed and will need checking.

Good luck with resolving the poroblem.

Pete

[Canuk]

Thanks to all for the input...and thanks to Don, I will contact the machine shop tomorrow to have the head rebuilt...

[Canuk]

Goes in the the machine shop tomorrow for repair..Thanks for the contact info Don...

[Canuk]

The head is off the get rebuilt tomorrow...The engineering guy suggested replacing the guides all around, skimming the head, re-seat the valves and port and polish...so should be good once it comes back...Here's a pic as she sits...

[251 ENG]

I think MED does oversize guides .

Or get a stepped sleave put in the guide hole and use a std one

[Smiffy]

Are you sure the hole is worn and it wasn't fitted with a used guide, by some expert or other..........

[Canuk]

Apparently a previous owner used to slalom race the car and did a lot of upgrading to the car, especially the engine.

The reason the guide shifted is the valve gummed up in the bronze guide and when the engine started it pushed the valve and guide down and off the valve seat.

I was talking to the engineering shop and they said that bronze guides absorb oil and over time can gum up.

He suggesated and recommended that I have all the guides replaced with cast guides...

The pistons, and valves and guides all looked in great condition although carboned up some.

The car sat (Based on speedo) for some 13 years after the respray and only did a 1000km

Anyway at least now I feel I know the car a bit better...

[Canuk]

Well after almost 6 weeks my car fired up back to life tonight... I'll tune the carbs tomorrow...Every thing started up OK..I cut the 'S" spring on the oil pressure release valve (ball Bearing) and the pressure has now dropped from 100Lb to 70LB....Thanks for all the input and thanks to Don for the info on Competition Automotive, they did a great job.

[12G940]

has anyone checked the ID of valve guide hole, bronze is the sacrificial lamb here, it could be just fine,
once shifted it is lubricated in service so little if any wear takes place. BMC upped the interference fit in the sixties as this was common on the first 'S's and reamed after the fit, this mainly cured the problem.

[Canuk]

I went off advice and had all the valve guides replaced (Cast iron)...The head was jet cleaned, new guides honed, valves re-cut and head skimmed.

It was pressure tested, so all should be fine now...They recommended an oil from Joe Gibbs that has ZDDP additives....so fingers crossed.