Triumph ST wont start - 5psi compression ?

Guy at work with a '06 Triumph ST used mainly for commuting and Touring found it wouldn't start. After changing the original battery and checking the plugs are sparking finding the bike still dead he took into his bike mechanic who advised him all 3 cylinders are all at 5psi under compression test.

Anyone hazard a guess whats wrong as they are currently scratching their heads.

 

Bad compression tester?? lol How about one of cams is not turning or jumped timing? Hard to believe head gasket for all 3 cylinders went at once.

I'd change mechanics also. Why is he scratching his head over this. Think about it. There's only a couple of things that would kill all the cylinders from not having compression all at once and so sudden. Not counting major internal explosion.

 

Wtf?

I am scratching my head that the mechanic is scratching his.From he little bit described a fuel system problem is my first guess and next step in search.

 

Well actually the next stage of diagnostics will cost real money so was just floating here for ideas. :smile:

They did ponder if thats whats happened but they reckon it would have slipped about 5 teeth on the cam which they haven't heard of before and need his ok to continue before pulling things apart to check.

 

Fuel

It is a fuel injected bike?

 

Wait a second

I think I am a pinhead......you are saying you only have 5psi? Not 5psi under spec?:crazy:

 

Thats right, compression testing showed only 5psi in total on each of the 3 cylinders.

 

ok

If tester is correct.....valve cover must come off and cam timing must be checked.I would not crank on it at all until timing is checked and valve clearance is checked. If valves are bent ,and it only takes a slight tweek to ruin them, you should be able to pick that up in clearance check.Sorry about my dip shit fit earlier.

 

Static leak down test is in order.....if no oil is visible at the head gasket/cylinder interface and the cylinders are not sealing...this would indicate valvetrain. I would go for a second compression tester and retest, before jumping to conclusions. It could also be that the starter gear set is hosed and isn't fully engaging, and therefore, not spinning the engine as it should.

You could also drop the exhaust, and pull the tb's and take a good look see at the intake and exhaust exhaust valve action while turning over the engine by hand. At this point, if the cams jumped time, or a cam snapped in half, and the mech rotated the engine with the starter, it is too late, as interference has already occurred.

 

Thanks, will pass it on to him.

 

Forget the comp test use a leak-down tester to get an accurate measure of what the sam hill is going on in that engine!!..

 

The funny thing is previous to the Triumph ST he bought new in 2006 he'd had 2 VFRs which had given him no problems, guess his next bike once the ST has been sorted should be a VFR again. :thumbsup:

 

I doubt it would take 5 teeth to not seal the cylinder it could be one or two. Wonder if the cam chain tensioner did something funny.

Leak down won't do much if the cylinder is not sealing at all. The 5psi most likely is just from the piston pushing backup. I'll bet you actually have zero seal. Even a bad head gasket will still give a lot higher readings. It could even be a broken cam chain. Just pop the valve cover and have a look see.

 

Update - The bike is with the local Triumph dealership who have been in contact with the parent UK Company who seem to be just as flummoxed. The Dealerships mechanic has taken the cam covers off and confirmed the Camshaft and chain are still intact, next they will be taking the head off to check the Valves and Bores insides.

 

I gotta bad feeling about this. I wouldn't think it would be that difficult to diagnose the issue..........

 

To the point

I had one that ran , but not well, very mild bend to the valves.Roll it up on TDC and plug test hose to cylinder ,and hook up to compressor,and the air will flow out of failed area.At 5 psi it will be quite clear whats wrong.:thumbsup:Have you looked at cam chain?

 

Sorry no updates as yet from his mechanic / Triumph Australia, the bikes owner dosen't want to harass them everyday but is also worried about how long they are taking. For those interested in a bit more detail he has also posted his problem on UKs Triumph Forum:

Triumph Forum Thread:
All 3 cylinders at 5psi - Triumph Sprint Owners Club

 

Confusing Update - They had taken the head off and advise the pistons and head has a high build up of carbon which is the cause of the no start problem.

Anyone know how carbon build up can cause 3 cylinders to have 5psi compression ?

 

If there is carbon on the valve seats, that would do it. Personally, this whole thing really sounds screwy. A modern fuel injected engine with carbon build up? To the point that an engine won't start?

For that to happen, I would think black smoke and horrible gas mileage would have been evident. The original post said that the spark plugs were found to be getting spark. Does that mean they were removed and examined, or that an extra spark plug was attached to a plug wire and the engine cranked over until a spark was seen? Had they been pulled, they would most likely have been carbon fouled, if this is indeed what the problem is.

I get the feeling there is more to this story than is being told, and I don't mean that from an accusatory or adversarial point of view. There is some information missing with regard to history or what lead to the bike's current condition.

 

Truth be told I only park my VFR next to his Triumph in the motorcycling space in works carpark and chat about bikes and different roads from time to time but he is a competent all weather biker and has owned 2 faultless VFRs before his 2 Triumphs but he also admits the Sprint has been used mainly to commute 15 minutes each way for the last 3 months.

He's going into the shop to inspect the headless engine today before they send it away complete to be de-coked which they say they have done before. Personally haven't heard anyone suffer this exact problem before but then they also service Ducatis so who knows.