TR25W- Exhaust valve problem?

[cpp01]

Hi all,

I took my TR25W out for a longish run (30 miles) on Saturday only for it to lose power fortunately close to home. On inspection the push rod to the exhaust valve had come out of place which I thought was very strange. Trying to refit the push rod in position I found that it was sitting fairly high but through a bit of bodging I managed to refit it in place, in doing so the component which goes between the push rod and cam shaft dropped back into the normal(?) height position. Now when I kick the engine over the inlet valve moves up and down a reasonable distance but the exhaust valve push rod/rocker arm barely moves at all. There is also an occasional 'pinging noise' but I'm not sure of the source.

The engine has compression, fuel and electrics.

Does anyone know what the problem may be? Being a pessimist I suspect the cam but I'm not sure how to work this out without strpiping down the engine.

Any thoughts/help would be greatly appreciated.

Thanks,
cpp01

[R]

From your initial description, and also being a bit of a pessimist, it sounds like you have/had a sticky exhaust valve.

This is where the valve sticks partly open in its guide - and you lose compression - and, depending on the engine, the piston can in some cases clout the valve. Not good. This is about the only scenario where the exhaust pushrod can escape. Doesn't sound like your valve was clouted, however, we can but hope.

Don't know about the cam side of things, but the follower could just sit there once the pushrod was not returning it.

Sticky valves are usually just a gummed up valve in the guide, and a clean will cure things. Rarely will they fix themselves, better to whip the head off and investigate. If its not gummy or even dirty, you'll have to investigate further.
Doing nothing is not a good option, reliability and not being stranded being at stake.

You running petrol with ethanol ?
Your tank got a liner/sealer in it ? Still all intact ?
This does sound a little like some of the odd things folks are seeing.

Sticky valves go back into the dawn of motoring though.
Your engine burn a bit of oil ?

[R]

P.S. What we probably should have asked first is how much valve clearance do you now have on the exhaust valve ?  Did you have to alter/adjust anything to get this clearance ?

Still wondering if something has broken in the cam follower dept downstairs, which is the other possibility, as you mention.

[Goldy]

I agree it sounds as though the valve has stuck and it may have bent the push rod. The only thing to do is take the head off and see what has happened.

[cpp01]

Hello,

Sorry for the slow response, been at relatives this weekend.

Thank you for your responses R and Goldy. I've not had a chance to examine things again but I do have some questions! Don't read them as an attack on your suggestions, just me trying to understand the problem better.

The valves were replaced about a year ago and have had less than 250 miles use. Does this make it any less likely that the valve has stuck, this combined with the fact it would have stuck after 30 miles of riding. I might not understand the mechanisms with which a valve would stick properly, but surely it would be at the start of a journey? Is it just a build up of dirt which would cause sticking or is it a tight valve expanding and sticking inside the guide?

I'm also quite surprised at the small amount of movement in the cam follower, I actually noted this before replacing the push rod (watched it using a mirror, the inlet rod appeared to move a lot compared to this one). I thought perhaps the exhaust cam follower had dropped which allowed the rod to fall out of place (indication of a failed cam shaft/cam follower?).

With regards to your question, there was a very large valve clearance (>>0.25 inches) when I started to look at the problem. I adjusted this back to spec but the push rod movement is so small it isn't really shifting the valve at all.

I'm not going to get a proper look at the engine until next weekend but look forward to any suggestions you have.

Thanks again for your help.
cpp01

[esometisse]

have a look at the cam and followers. Your problem goes deeper than a sticking valve. There is no way round a thorough investigation!

Good Luck
Andy