Engine Sounds Like A Machine Gun

Hi Guys, I posted about tappets yesterday, I have now had a better look (1998 Trophy 900). My clearances all check out spot on - 10-15 inlet, 15-20 exhaust. There is no sign of cam damage, the cam retaining bolts are all tight. When starting from cold she sounds ok, usual bit of Triumph rattle. When I rev her though she sounds like a machine gun at the top end. I'm starting to think a valve is sticking - is that plausible? She seems to rev ok, no sign of overheating, I've changed the oil and don't see any contamination in water or oil. Thoughts?

 

Tensioner looks fine, it sounds like it's coming from the area of the top of the middle cylinder. It's weird that the tappets measure fine, It's almost as if one of the valves is closing too slowly.That's the only thing I can think of. I now have to decide whether to take the head off or just bung my spare engine in there.

 

Fairing was off, I don't believe it's clutch noise. It's also way louder than normal tappet noise, I'll try and get a video. Inlets were all about the 12 thou +- 1, exhausts were all under 20, except one that was bang on 20 - the middle pot. This is like nothing else I have ever heard, you can easily hear it over the exhaust noise. I'm still sure it's top end, I didn't know the liners had to be messed with if the head is removed - that probably tilts the balance in favour of sticking my spare engine in it. It tends to come and go a bit, which makes me think sticky valve not returning fast enough, I don't know how plausible that is though and would only find out by taking the head off.

 

I can't upload a video :-(

 

I'll try that. I turned it over with the cover off and plugs in but it doesn't make the noise at cranking revs. Sometimes it's quiet at tickover but the noise starts again when it's revved, which is why I am thinking something is sticky but I would have thought unless a valve is bent it would have worked itself loose by now.

 

LOL, sorry Oldyam, that's a decimal point issue. Should have read 0.12mm. Anyways, just had another look in better light. I think my cams are knackered. When looking at the middle ones they look like something naughty has happened in there. What do you reckon? Sorry if it takes a while to load I have used quite a high resolution.

 

Just to clarify on the clearances, sorry I have always used thou up until now but I couldn't find my feeler gauges and the only set I could buy were metric. The clearances are correct at 0.12 inlet and 0.17 out, give or take 0.01 or so.

 

The one in the photo is the worse one, the other exhaust on that pot looks nearly as bad, the intakes not so bad. It really does sound like the noise is coming from the middle pot. I think I will try a cam change and see where it takes me. When I just started it up from cold and let it idle it actually sounded ok but get her up to 1200-1500 revs and she starts rattling again. Thanks for your input, it's nice to have a sanity check sometimes.

 

I just found a complete head for sale at a sensible price but it's for a Thunderbird - it's part number 1150558. I could get the cams and followers out of it that way I don't have to disturb my liners or anything. Anybody know for sure if they are compatible? I know my cams are marked 1140345 if that helps?

 

Just been doing a ton of research, apparently there are 3 cam profiles - green blue and red. Mine are green the Thunderbird ones are blue so would not be compatible. They have a much shorter duration and less overlap apparently. I figure that the cam swap should be the first step as it's the most likely source of the problem and it's the easiest thing to do. I have bought a pair, the only down side is that a complete head would give me some shims to play with as well. It seems a bit of a ball ache on this engine if you don't have the special tool that allows you to swap shims without removing the cams. The number is what I took off the cam fitted in my engine, it comes up on a google search.

 

The plot thickens. I just removed some of the oil that went in it yesterday, it's badly contaminated with something. It looks like there is some fine black dust in there and it's gone cloudy. I think the previous owner put something in there to try to quieten it down. Before I do too much more I will drain it down again, flush it and put new oil and filter in. Could be a new motor is the best / safest option after all. I don't know, it's making my head hurt. I need beer.