offthefront

Cig ...your loosing me ..you went to a new cam with same spec's and then had problems ? the valves are SS ...also this valve was brand new ...So I dont see how corrosion could do it ...so soon ...they did just the EM's last time but pluged it with clay ...only 5-6 lbs .. to me thats not enough ...

blue thunder

What are the valves? If not severe duty, and if engine is run out of tune (lean for instance) you can get this result. It will trick you because the exhaust valve will get hot and start to move, then start sucking water and then you get the result you have, or worse the valve head pops off. If its not that, then the risers most likely. Do you run the 3" spacers by chance? I could never keep that crappy system from leaking... terrible design.

This time put in top of the line manley valves for starters. Once running again, read the spark plugs in primary and secondary circuits of the carb. and determine state of tune.

BTW, all valves are stainless. But there is a large difference between high quality and regular grade, as wannabe was saying. You want one piece, severe duty, with no necking of the stem. Preferrably 3/8" stems.

BT

cuda

A stuck open intake will draw water in the cylinder.

blue thunder

Actually, if the risers were leaking the water in the cylinders would cause severe damage due to increased compression and or hydrolock. The fact that no major damage is done indicates the valve is already bent before the water infiltration. Therefore the water is being freely pumped into and out of the cylinder via the bent exhaust valve. Your valves are weak and your tune suspect... (nothing personal )

BT

Lmarth

Blue Thunder/Cuda-- Good input on water ingestion/reversion and whether this Jasper long block contained marine components. But I'm still not hearing why a number of valves hit the pistons. I'm willing to bet you could open those valves to the point where there was coil bind and still not hit the pistons. Maybe the valve heads warped to the point where they weren't square to the valve stem? I apologize for sounding like a cynic but I'm just wondering if there's an automotive cam and valves in that motor. It definitely sounds like water is part of the problem cause or is the result of some other problem(s).

offthefront

Only ONE valve (exhaust) has kissed the piston . #5 I believe ...same one two different times ....Jasper knows it was a marine motor ...I would think they build it to spec ...talked to them today and they want us to check timing gear/chain for wear ( i dont see how with 20hrs) or damage ...we will check it .... Valve warp ? from the revervsion ? .... there is one scary thought in my mind is maybe it IS something I am doing comming off a plane ....My mechanic took the boat out and ran it for over an hour with WOT runs and had no problems ....I ran it 15 mins @ 4000rpm and it broke ..When I come off a plane I dont slam on the brakes but I dont take a mile to stop either ....I ease off plane and then throttle all the way back ...maybe I need to keep 1000+ rpms till boat settles ? I cant believe its that sensitive and also have silent thunder so there is no full blast from wake in the rear ...also all he plugs are out of the bottom of the platform wich menimizes water in box .....

By the way I dont take any of this personal so keep em commin ...mike ..

Lmarth

Mike--Here's what I'd do. I'd put #5 at TDC, pull the spark plug and pump it up like I'm going to do a leakdown test. Then I'd remove the valve spring for the exhaust valve and replace it with a soft sring so you can check the clearance to the piston with the valve at it's normal maximum lift (you'll need a dial indicator). The results of this will hopefully explain why that exhaust valve has TWICE hit the piston. I agree that it's unlikely the timing gear/chain is the culprit with 25 hours but you have to check for everything. Who knows, maybe the keyway was broached wrong on the timing gear and the cam is way off (advaced/retarded). Now since we're concerned about water ingestion/reversion, did Jasper confirm that the cam is a Marine cam with appropriate Lobe Separation Angles to avoid reversion? I don't think with a Bravo setup that you should be extra vulnerable to your wake coming back up into your engine though the thought crossed my mind ( post #31 ) after you said it ran great on the hose until you took it out on the water. Which takes me back to confirming that you've got a Marine cam in that motor. Personally, I'm extra careful coming off plane. After making sure my wake doesn't catch up to me, I put both motors in neutral, bring the rpm's up to 1500-1800 to get a little water pressure to try to minimize any steam pockets,etc. Probably overkill but it's worked for me so far. Good luck! Lou

Liberator21

If it's only #5 having the problem, did they check guide to stem clearance on that valve? If it's too tight, it could bind and cause the valve to hang open when it gets hot. I think the wrong cam or bad timing chain would affect all cylinders, not always #5. When you put the heads back on after the first repair, did you put them on the same sides you pulled them from? If so, concentrate on the head first. If you swapped sides and #5 went bad again then I'd look elsewhere.
Just my $.02

Wobble

I have seen a several problems with valves hanging in apparently stock motors. It seems that there is always some water vapor in the area of the exhaust ports. It seems that it is very important to make sure that the exhaust gasket and exhaust manifold do not overlap any part of the exhaust port on the head. If it does it can cause any eddy of trapped water vapor that will dry out the oil film around the exhaust valves causing either accerated valve guide wear or seizure. We fought a similar problem with a 502 for months after replacing the exhaust with merc replacement. After trimming the gasket to match exhaust port and matching the exhaust manifold to gasket the problem never returned. Don't really know the science in this but it seems possible.

Mark

cig1988

Mike, just trying to help you out. I replaced the cam because it was worn, once the new cam was installed the reversion problem started. I only ran the engine in the driveway but had I ran the boat WOT in open water, I'm sure it would have been a simular problem to yours. It drove me nuts for weeks on end and with help from Marc @ BAM he helped to steer me in the right direction.
I wish I had a pic of the top of a merc riser to show you the differance. I can get a pic of the aftermarket riser if you want. Alot of good advice here on this thread for you to follow. Hope it all works out for you.
Stan