Need help troubleshooting engine starting problem

[tdonoughue]

Zero compression on two cylinders is bad.

Yes, it is time to pull the valve cover. You may find a broken timing chain... That is my current guess. At any rate, it ain't good, even if it isn't that. Sorry.

 

[zipper]

Other than a slow crank over, are/where there any other sounds coming or lack of sound from within the engine during crank over? Like metal hitting metal, pistons hitting valves. These are interference engines, at least the MR-1 HO's are and if the timing chain is broken, open valves' stems will bend when you crank the lower part of the engine. Verify that the camshafts are turning with the crank. But I doubt a broken timing chain on an MR-1. Swollen wear ring? And the 10.6V raises an eyebrow, slow crank and that is too low to fire.

 

[SprockJohnson]

Valve cover partially removed and I was able to observe the cams and timing chain all intact and rotating like they should. Timing chain tension appeared fine and nothing visually jumps out as broken or damaged. We used a lighted bore scope and checked the inside of all the cylinders with the plugs removed and 1-3 had heavy carbon buildup and #4 appeared noticeably cleaner. Going to be removing the valve covers completely as well as the intakes to look at the intake valves and to see if they are sticking and if so then to shoot them with solvent. I haven't checked the valve lashing but will do so with the valve cover off and might as well check the other engine too.

If it is indeed sticking valves, what are the chances that 3 out of the 4 cylinders would stick all at once?

 

[tdonoughue]

Well, if that turns out to the be issue... pretty darn good chances!

Looks like positive progress. Heavy carbon buildup is consistent with a stuck valve, but the cleaner 4 is not consistent with no compression on 3 and 4. Sounds like you are doing exactly the right thing, tho. I think then we are to the point where I am agreeing more with @zipper (oh wise is he!) with the stuck valve...

 

[zipper]

I was not thinking stuck valve, but very possible. I was referring to an open valve head being struck by a piston if the timing chain is broken. And it is not. Bad plugs/bad gap will also build carbon. He says he has spark on all four. Pull the plugs and hand crank the motor to check for resistance from the wear ring, for slow crank. 10.6V is still in my mind as a cause for slow crank and not firing up.

 

[SprockJohnson]

I removed the head from the engine and as it turns out all four cylinders had stuck valves. Removed all valves and will be cleaning the buildup on the stems of the valves and the ports on the head. Nothing appears damaged, but there is some serious amounts of buildup on both the valves and the head. Dirty fuel? Bad detonation? I got the impression that this wasn't an overnight amount of crud which had built up on the head and the valves.

 

[WREKS]

Is it possible engine was overfilled with oil? Is the bottom of the airbox dry? What is the condition of the filter in the bottom of the air box that connects to the oil separator hose?

 

[SprockJohnson]

Airbox is dry and filter appears fine. Not sure about any other filters for the oil separator. Where would that be? All I see on the bottom of the airbox is the intake hole and the drainage hole/ duckbill valve.

 

[tdonoughue]

Could just be serious hours. Or bad gas. Or lots of sitting and not much running at good speed. Hard to say. But good that you located the problem.

And that @zipper was right on the stuck valves (wink).

 

[SprockJohnson]

So as it turns out the stuck valves were not the only problem... I rebuilt the head by cleaning up all the valves and installing new valve seals and after starting the engine noticed a goodly quantity of exhaust smoke in the engine compartment which I couldn't immediately find the source of. I located the source of the exhaust and it was coming from the breather hose which goes back into the air filter box. I checked compression again on each cylinder and observed 1 and 3 were in the 160psi range but 2 and 4 were only around 70psi. Bad rings. Total disassembly of the crankcase and after measuring found that the cylinders were within spec but the rings and pistons had worn down enough to need replacement. Still waiting on parts so we shall see if this is indeed the root of the problem. I figure the nasty oily blowby being sucked back into the intake is probably what fouled up and stuck the valves over time.

 

[Canuckjetboater]

Hi all,

New to this forum but not new to jet boating. I have a 2006 Yamaha AR210 I bought new in 2006 and although I haven't had many problems over the years this one is turning out to not be simple to diagnose.

@SprockJohnson ....do you have easy access to a Yamaha dealer? You have done or everything I can think of has been suggested. Respectfully suggest its time to download and review the info from your management system to see if a code or fault shows. I was thinking stator but your engine(s) should start from the batteries and at least run for awhile if the stator was kaput.

 

[tdonoughue]

Wow. That is a lot of repairs. How many hours are on the engine?

But nasty oily blowby would make sense to jam up the valves like that...