low compression but leak down test within specs - 2014 gtx 155

[cykrus]

Hell all, I recently purchased a project 2014 155 s 165 hours. Yes i know a pain to work on but lucky me all bolts came off without snapping and i got to the engine bay. I was told that this ski overheated .. i looks on the history with CanDoo and i saw maximum coolant temperature 136 degrees celsius. The running rpm history show the ski was not beaten most of it is under 5000 rpm.

The ski starts easy (i only tested it outside of the water) but hesitates when i give it a brief acceleration ...

I did a compression test with a compression tool and i got 95 , 95 and 120 psi. I don't know how accurate my tool is that seems like a low compression. There is no oil in the water and no milky oil. For the 2 cylinders that had low numbers i poured a teaspoon of oil in the cylinder and redid the test and i got the same numbers so it does not look like the rings are faulty.

Pulled the oil filter absoluteness no metal flakes. Oil looks clean. Extracted the oil and i let it sit, no water in oil.

I then removed the engine, removed the rocker arm and did a leak down test. With 90 psi on the tool I got under 10% leak on cylinder 1 (the one with 120 psi) and under 20% on the other two. The air was manly escaping on the exhaust port. The fact that the engine is out (so no more coolant in the engine to watch for bubbles) and the air coming from the exhaust how can i diagnose if my head gasket is blown?

The ski did not run for the past 2 years (i see the last tag 2023 on it) I suppose the exhaust valves might be a bit rusty; running the engine it might reseat them, right ?

According to the manual under 20% i am within specs .. .but then why the low compression ?

All of my test were done with the engine being cold.

Now the compression test low numbers contradict the leaks down test that show the engine is within specs. What do you suggest the next step is? Should i pull the head and replace the head gasket ? What else would you do ?

Thank you

 

[dcm0123]

136C is 276F which is very hot.
Probably burned valves and possibly seats.
Since the engine is out, might as well pull the head and fix it right. If they are burnt, will get worse over time. Check for a warped head as well.

 

[cykrus]

thank you for your answer. i got the head out Tomorrow i will get the valve tool to remove them. Once removed the vales can it is "visilble" if they are burned or bent ? What are the signs to look for? Can i just replace the 4 exhaust valves and seals that were leaking ? I called the dealer and it is 100 $ / valve not including the seals .. that would be crazy .. to redo the head 1600$ ?

 

[dcm0123]

May not be easy to see a warped or burned valve. I flipped the head so the valves were up and poured mineral spirits on mine to look for leaks. You could use Prussian blue dye and lap them to see if they are warped and look at the flat on the edge of the valve head for signs of melting.

You can buy a set of aftermarket "solid core" valves for $400-600 from Green Hulk. I suggest you research the aftermarket valves before you buy. At a minimum lap the new valves to make sure the valve seats do not need work.

You could also just replace the ones you find burned or warped and lap both old and new as stated above.

Others who have had experience dealing with burned valves may have a different opinion on this. You bought a 155 engine so you obviously are not intending to race this.

 

[cykrus]

thank you so much for you advice. I have removed today the old valves, they look ok .. i will turn them on a mirror glass (i saw this to be the procedure to see if they are blended). Also i will try to lap them as per the manual specs. I measure the stem diameter and the contact surface and I am within specs. I suppose that the engine sat for a while and the 2 pictons are a bit rust. The mating surface of those is a bit more dark than the one that seals ok. Tomorrow I will buy lap compond and go as per manual and then once lapped (and clean) i wil be able to measure the mating surface to see if I am still within specs. As i read never mind if only lap the old ones or install new valves the seals needs to be changed, right ?

 

[dcm0123]

You should replace all valve seals. You will need to pry off and then press the new ones on to the head. Lubricate when you press on.

You should clean all oil off the cylinder head and valve heads, then coat the valve seats and mating surface on the valves with blue dye (Dykem) to make it easier to see imperfections after lapping.
Lubricate the valve guides with oil. I typically chuck a low variable speed drill on the valve stem and use it to rotate the valve while mating and un-mating the grinding surface every couple of seconds to spread the lapping compound and oil which it is embedded in.

When done, disassemble and wash everything off to remove all traces of the lapping compound. Good job for gunk engine cleaner and a high pressure hose.