85 supra comp

recently aquired this boat at auction and is too late to run it.
boat was sold by marina to a guy for 9 grand and ran good durring sea trial. He picked the boat up next day and had problems first time out.
he told me the engine got hot and he was towed in. the marina replaced impellar and he tried it again.... Same result.
the marina said the would make it right and did a complete tune up and it still wouldnt run right. On the third time out, engine running rough, no rpm, mabe 3000 or so. He described an explosion under the cover and engine stalled. After getting towed back again the marina replaces exploded exaust hose on drivers side and cleans up mess. Guy gets his money back and marina goes tits up shortly after.
I purchased the boat cheap and it is in stellar shape engine problems aside. PCM 351eng. has 320hrs. but i detected some silicone around frost plugs.
engine still has points set up that i will change in spring along with examining raw water pump and clean out exaust system.

Im guessing that the timming advance may have gotten stuck and retarded timming caused high temp and exaust bomb to happen.
the oil is clean and there is no evidence of water in valve covers.
the guy told me that when he initially tried the boat that it ran 50mph and did not get hot.

Any feedback would be appreciated. Need to formulate a plan for the spring!

too late to run it on a hose? is it winterized?

i'd check everything you were told...impeller, risers/exhaust manifolds, distributor and tune-up parts, carb. are you near saltwater?

i don't think timing advance would overheat it enough to melt the exhaust hoses. sounds like an overheat and backfire. check all the exhaust hoses, you'll need new gaskets after checking the risers and all...skidim.com has it all and they know old supras.

Look closely for any impeller remains in the water system, they can restrict flow & cause much grief. Don't ask how I know, but I had a similar experience wit a 95 Comp w/351. Once I realized replacing a bad impeller requires nor just replacing it, but also locating ALL the missing pieces, I had a great boat.

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Originally Posted by Salty87

too late to run it on a hose? is it winterized?

i'd check everything you were told...impeller, risers/exhaust manifolds, distributor and tune-up parts, carb. are you near saltwater?

i don't think timing advance would overheat it enough to melt the exhaust hoses. sounds like an overheat and backfire. check all the exhaust hoses, you'll need new gaskets after checking the risers and all...skidim.com has it all and they know old supras.

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It was winterized when i got it.

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Originally Posted by Pdowling1

Look closely for any impeller remains in the water system, they can restrict flow & cause much grief. Don't ask how I know, but I had a similar experience wit a 95 Comp w/351. Once I realized replacing a bad impeller requires nor just replacing it, but also locating ALL the missing pieces, I had a great boat.

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The guy told me that the old impeller was not destroyed, but that says nothing of previous ones.


how far in do you need to search for debris?

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Originally Posted by RonnyD

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Originally Posted by Salty87

too late to run it on a hose? is it winterized?

i'd check everything you were told...impeller, risers/exhaust manifolds, distributor and tune-up parts, carb. are you near saltwater?

i don't think timing advance would overheat it enough to melt the exhaust hoses. sounds like an overheat and backfire. check all the exhaust hoses, you'll need new gaskets after checking the risers and all...skidim.com has it all and they know old supras.

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It was winterized when i got it.

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no salt water here. The guy told me it exploded under the eng. cover and the exaust hose was nearly gone. what could cause this to happen? Raw fuel? Restricted exaust flow? Reminds me of blowing up a car muffler.

Explosions from under the motor box are never a good sign. Do a compression test and a leak-down test if possible. You need to know what you're working with before you spend any money on that motor.

DKJ

Not sure about the explosion... I assume since you mentioned hoses and cleaning up 'the mess' you were speaking more of a burst cooling hose. If thats the case aggressivly trace cooling system, if it back pressured enough to burst a hose, then as people have mentioned, your water pump is probably ok, possibly occluded somewhere else in the system. If you had an overheat I would go ahead and replace the thermostat & clean out the housing. Closely inspect the transmission cooler for blockage. Make sure your raw water pick up line isnt restricted. Basicly trace the raw water cooling system and make sure everything looks good. When you can run it, make sure the block is filling and not just bypassing through the manifolds. If the 'Explosion' was a backfire; start simple- Air flow, fuel mix and exhaust. Make sure your flame arrestor is clean and unrestricted. Some people tape or seal the arrestors during winterization. Make sure your vent hoses are in place and open. I would replace the PVC valve (inexpensive required maint anyway). Inspect the jets in the carb and as you mentioned change points or upgrade your ignition system. New plugs wires and ignition coil would be a low cost "tune up" since it sounds like your marina may not have done much for you. Last but not least, make sure the flappers on your through hull exhaust are intact and working. If they are letting water in when the boat comes off plane you can get back pressure from the water flowing up the exhaust systems, causing the symptoms you have described. Good luck.

Sorry, thats PCV valve

Your comments that it ran good in sea trials, but later began to run rough and hot, make me think someone got sloppy with the last tune up. Timing, either ignition timing or valve timing, can cause all the symtoms you describe. I would first determine firing order, and verify the plug wires are connected to the correct plugs. I am more of a Chevy small block guy, but I do know some Ford small blocks have an unusual firing order. I would check a manual, if you don't have one you can download one from the PCM website, and make sure the "mechanic didn't cross up some wires. Then you make sure the distributer is timed correctly. This can be done staticly, but is best done, while the engine is running, with a timing light. My thought here is the mechanic may have adjusted the timing during tune up, and failed to tighten it afterwards, which would alow it to move and get all screwed up. This can cause igition in cylinders at inappropriate times. If it occurs too late, the explosive fuel mix is ignited with the exhaust valve open and you get external combustion in the exhaust manifolds, instead of internal combustion in the chambers. So check for a loose distributer clamp, but check timing even if it is not loose, because somone could have tightened it after the fact. My bet is on this being your problem, but it is also possible that the valve timing is off which can also cause the same symptoms. Example, if the exhaust valve opens during igintion or compresion. This would be caused by a worn timing chain skipping some teeth and getting the cam out of sync with the crank. This usually doesn't happen until an engine has a lot of wear on it, and I would not expect it on a boat engine that has had reasonable care, unless it had an extremely large number of hours. Hope this helps.