My 496ho had a miss and I thought it was a plug. My mech started it up and told me it was smoking and had a wet plug. No antifreeze was noted to be in the oil and coolant was not low. Comp and leak down revealed 60 psi. and no holding pressure. He told me he thought it is a stuck valve . Offered 2 options . Pull the head and see how it looks or A COMPLETE LONG BLOCK. If it is just one valve that hit the piston can I not just have the head done, hone the cylinder and replace the 1 piston rod and bearing?

Any thoughts appreciated

Chris

you have to be sure what the problem is...if it's a valve,no need for a long block,in my opinion...just put oil in the faulty cylinder,and take another compression test...if compression goes up,it's probably the rings...if it stays the same,probably a valve...have both heads redone,and you're good to go...jmo

even if valve hit piston, doesn't mean last rites for that piston. unless the dent is within 1/4 inch of edge, in which case it probably is jamming the top ring. sure he wants to do complete engine. gets paid more then he has a good engine to sell!! win win, for him...

I would before you do a complete engine out and tear down do a leak down test in that cylinder with some compressed air an identify where the leaking compression is going. It could be a stuck valve, but just pulling a valve cover will identify that and any other valve train issues that will be visible. In any event if its a valve issue, you should be able to just have that head pulled and repaired provided the piston and cylinder are not damaged and the other cylinders all had good compression.

Don't always assume the worst in a case like this.

When in Doubt-Check it Out!

How many hours on this engine?
Kept in a slip for long periods?
Any other issues with the engine?
Do you have any mods upgrades or headers on the engine?

Some of this info is helpful when trying to evaluate a possible issue in an engine like the 496HO.

Best Regards,
Ray @ Raylar

when in doubt-check it out.i like that ray,do believe i will start saying it.

The engine only has 100 hrs on it and is bone stock. It did over heat to about 190 once last year due to sucking something through the outdrive but ran pretty well the rest of the season. Last ran it on Thanksgiving day and after going through a long no wake zone it loaded up a little and stuttered when i first got on it then it cleared up. My mechanic did a comp and leak down on that cylinder and said it had 60 psi and total leak down. The thing that really bothered me was said it was smoking. I live in south florida so it something freezing and breaking is not an issue. The boat is always kept on a trailer in a storage lot. Oil and filters are changed every year which is about 30 hrs a season and always run non ethanol fuel. Can you re-do just one head? and get one more season. The boat is only worth about 10K in this economy. I would never do one head and sell it to someone without disclosing that, I just would like to get another season out of it as I was planning on a new boat next year.

Chris

you can just do 1 valve if that's all that is wrong. you aren't robbing anybody even if you DON"T tell them you fixed something. anybody buying a used boat on the assumption that nothing on it has ever gone wrong and never will...but yes there is nothing wrong with doing only 1 head if compression is good on other side. boat motors rarely live long enough to wear anything out.

Ok more clues . I went to the shop today and one piston has a small "scratch" from the valve. Not even a mm deep. It was also noted there were no turbulators installed on the exhaust. So I'm thinking the valves were getting condensation on them and that led to a sticking valve and low compression. Only troubling thing is he said it was smoking a decent amount. Could valve guide and seal leak enough oil to smoke a decent amount? All thoughts or ideas appreciated.

Chris

It could smoke out the exhaust from a cylinder with a bent valve that is dropping compression so much that the lack of compression in the cylinder will allow more crankcase oil to pass the rings and burn in hot exhaust stream. It takes compression in a cylinder to help seat the rings with pressure from the top. Is the valve bent? How is the valve guide and seal? What condition are the cylinder walls in that cylinder versus cylinders with no compression issues?
Sounds like the head must already be off? Was there a lot of evidence of valve seat and valve rusting on this valve indicating condensation was the issues.? Does the boat sit in the water a lot (slipped)?

Best Regards,
Ray @ Raylar

To me the head and valves did not look that bad but there was a small mark on one piston. It was a circle shape just like a valve. The mark at the worst spot was less than 1mm deep. He did a comp and leak down on the other head on all cylinders and the back cylinder was 20 psi lower than the the others with pretty bad leak down but I dont remember the #. The cylinders themselves look like new.I don't see any scratches.The boat sits on a trailer at a storage lot. Not in the water or on a lift. It was on a lift for 1 season . I do boat in saltwater 100% of the time, flushed after each use. I was quoted 1600 to have the heads sent out for repair including gaskets and installation. If I can get 2 more seasons for that I will be happy. Getting a new boat by then. Worst thing is its a 1600.00 gamble not knowing if this will fix it.

Chris