stuck valve update

Not that it matters, but I did manage to get the top end torn down on the bike I just bought and thought I stuck a valve in the first mile of riding. The left intake is bent and had nicked the piston twice. No real damage other than the valve, Guide clearance is good. I ordered a new intake and should have next week. Hopefully I'll have it on the road in a few weeks and all will be good in Norton land again.

Yeah serves ya right for breaking it in harsh like you stole the thing : )
Just a nod to the extra life and time that must be spent to get what you want/need in a Commando yet no fault of your own, but choice of hobby.

hobot

Musta read too many Hobot stories over the last 8 years :lol:

Head is done will try and get darn bike back together this weekend. Given I can get the defective head bolt I ordered to thread properly.

britbike220 said:

Head is done will try and get darn bike back together this weekend. Given I can get the defective head bolt I ordered to thread properly.

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So it stuck and then hit the piston? Any idea what caused it to stick?

Dave, not sure. The guide seems ok, perhaps just being a new motor, tight spot or lubrication wasn't enough? Just hope it doesn't happen again..................

I can think of two reasons for a valve to stick: 1) incorrect guide/valve clearance on initial assembly 2) valve "kisses" piston and takes a "set" that prevents it from returning. In the second case it is common to find that the old (really old) valve springs were reinstalled.

In the mid 50s valve spring technology/material was in such a state that Mercedes invented the desmodromic valve actuation system so that they could consistenly finish races with the engine running on all cylinders. By the late 60s-->mid 70s valve springs had come a long way. but were (by modern standards) still pretty primitive.

If you are doing a valve job replace your valve springs, the ones that the factory installed may feel incredibly stiff, but consider that at 6000 RPM the valve experiences an opening acceleration of near 1500 Gs---the standard retainers and collars that statically weigh a few grams dynamically weigh a few kilograms!! A porperly matched set of inner/outer and insulator, if fitted are crucial to reliability, relativly inexpensive to boot.

RS

"Just hope it doesn't happen again.................."

I'd be real reluctant to just install a new valve and hope it doesn't happen again. Something caused it and you need to find out what and correct it. As noted, perhaps valve spring, perhaps lack of lube. In either case there is a problem to be fixed. Was engine running ok before teardown? If so, one would tend to believe that something in the rebuild caused the issue. Was the head or barrels milled so as to reduce the clearance between valve and piston? Were different pistons installed that may have done the same? Was the oiling system compromised somehow - were the rocker spindles mis-aligned so that oil was not delivered properly; did the spindles rotate even after installed properly because the keepers failed to adequately seat in the spindles?

There's a whole bunch of stuff to check to ensure this doesn't happen again...

Mike, The old friend that installed the new valve did check everything he could. I trust him implicitly and he has been doing engine rebuilding for around 30 years. The head has not been altered, the guide appeared to be ok. the new valve is seated correctly and all other parts invloved check out ok. Basically there is nothing visibly wrong at this point. With the old valve being bent it is pretty difficult to figure out what went wrong. Everything appears and measures correct in assembly. You are right something caused it, but short of doing the necessary measuring and assembly I cannot explain why this happened or if it will happen again w/o running the motor. This is a case where I'll keep the fingers crossed. If it does happen again, I'll be tearing it down again an trying harder to find a reasonable answer.

The two things I have seen that caused a valve to stick were old gas and desolving tank liner.
I did a valve job on a Ford Pickup some years back, while it was in the shop the owner asked me to check out the fuel tank switching valve because his auxiliary tank didn't work. So a week later we gave the truck back to the customer with new valves and guides and a nicely running motor, WITH a new fuse in the fusebox for the tank valve.
The next day the truck came back on a hook, zero compression. What we found was all the intake valves were stuck in the guides. We had to use a press to push them out. They were glued in place.
What we found out was the auxiliary tank had not worked for " a couple years" The customer had switched to the aux tank on the interstae and the old gas got run through the motor. He noticed it starting to miss and pulled off an exit ramp and the motor just died as he stopped. Expensive lesson. Jim

In the mid 50s valve spring technology/material was in such a state that Mercedes invented the desmodromic valve actuation system

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Sacrilege!! :shock: :lol:

Mercedes did not invent the desmodromic valve system, only a desmodromic valve system. There were several such systems prior to the Mercedes racer of the '50's, including a patent by one James Lansdowne Norton in the 1920's!! Mercedes was probably the first truly successful application and none of Pa Norton's designs was ever used in an engine. Of course Ducati is probably the most recognized user of the design.

http://members.chello.nl/~wgj.jansen/text/Walker.PDF

Jim, the ford truck sounds pretty much like what happened to me, but I have no tank liner and I believe the gas was new, at least no older than a couple weeks in my bike gas can. Doesn't mean it wasn't bad, but there isn't really anything to pin point. You are right about expensive lessons.

About five years back we had a four or five of the bent valve syndromes happen. In each case you would find a heavy carbon build up on the pistons flakes of the stuff. These were only counting bikes with metal tanks. We haven't heard from anyone in a while with that problem. Mainly it was older riders who never rev out the motor. “Old Man Syndrome”.
Wearing the hone job out before breaking in the rings and making them fit the cylinder. That gives oil a way in to the top of the piston that kills the mixture and on goes the carbon.

britbike220 said:

Jim, the ford truck sounds pretty much like what happened to me, but I have no tank liner and I believe the gas was new, at least no older than a couple weeks in my bike gas can. Doesn't mean it wasn't bad, but there isn't really anything to pin point. You are right about expensive lessons.

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I suspect if the gas did not smell bad then it wasn't likely the problem. When we tore into the Ford truck the smell of bad gas was hard to miss. I have heard of some gas additives causing the same problem some years back. I think it was some kind of octain booster.
Of course if the carbs and fuel lines were full of old gas that might be enough. Jim