Just got word back from the mechanic and there is a knock now between 1500 and 2000

[bluecollerboater]

I just got word back from the mechanic. my engine which is a 1994 volvo penta GiPMDA has a knock. The #4 cylinder had a sunken intake valve and the #3 exhaust valve was burnt. He sent the heads out to be rebuilt put it back together and there is now a knock. he says i need a new engine. I was running the boat in my yard for weeks trying to diagnose it and that knock was never there before. I knew the #4 and #3 had lower compression I knew it was from the intake on #4 and I knew it was exhaust on #3. He never ran it when I dropped it off. He took the heads off confirmed what i said about #3and #4. He puts it all back together and is telling me there is a knock. I went there to hear the knock and it is only from 1500 rpm to 2000 rpm the oil pressure is at 40 psi at idle and climbs with rpm. no noise before or after that. we ran it in neutral in a test tank. It is definitely a knock not a ping or a tap. My question is could he have set the timing wrong or left a rocker loose or something. I know there was no knock before he worked on it. Just trying to figure out what i should do.

 

[Grub54891]

Re: Just got word back from the mechanic and there is a knock now between 1500 and 20

Well,having 2 cyl low on compression could have hidden the knock. Now they are up to normal,making them knock. No way I can write that in stone but it's a thought.
Grub

 

[bluecollerboater]

Re: Just got word back from the mechanic and there is a knock now between 1500 and 20

I think you may be correct.

 

[bluecollerboater]

Re: Just got word back from the mechanic and there is a knock now between 1500 and 20

So I heard from my local volvo penta shop. There is definitely a lower end noise. I asked him if he pulled each plug to isolate the noise he said they did but it did not help. I asked him how much I was in to him for? He said they have an hour and a half into it so it would be $ 175 this is after having the boat for three weeks. Basically he told me it was a older engine and he wouldn't be comfortable fixing it and warranteeing it. He did however offer to sell me a new mercruiser engine. Does anyone in Massachusetts know a good mechanic who will actually diagnose what is wrong with my engine? I will get the boat back tomorrow or Friday and start doing some testing of my own. Mostly just venting here. It really steams me that most mechanics (at least the ones i have been dealing with)just want big money to swap out parts and not diagnose and fix what is there.

 

[insttech1]

Re: Just got word back from the mechanic and there is a knock now between 1500 and 20

I am just curious but when the heads were "rebuilt" what exactly did they do?
A full rebuild? Replace springs/rockers, etc....or just two valves and/or seats?
Did they even tell you? Receipts?

If he says you need a new engine, does he say why? Maybe a bad cam, or crank?
What are the compression numbers like now after that work has been done?

I agree that I would be asking more specific questions before dropping money into a block.

If it truly is bad, you can look up places like Michigan Motorz to get a new short block (since supposedly you have a "rebuilt" head) and probably save thousands....just sayin'.....

 

[Walt T]

Re: Just got word back from the mechanic and there is a knock now between 1500 and 20

Ahhh yes, the old "throw parts at it" mechanics. Try readjusting valves, verify ignition timing, verify compression, check each cylinder with a borescope. Assume NOTHING. Use a mechanics stethoscope to locate the knock. Remove all drive belts, run it. I would say verify exhaust shutters if it were a Merc. But definitely put the stethoscope on the exhaust and the bellhousing in case it's a coupler. This is called elimination and if all these don't bear fruit then the inner engine is about all that's left. Find an old cranky mechanic and have him listen to it. He'll know in a second if it's a 'death rattle'. Give him a six pack of Geritol for his help.

 

[dypcdiver]

Re: Just got word back from the mechanic and there is a knock now between 1500 and 20

I go with Walt T.