3.7 L Compression Problem

[DHPMARINE]

Just installed an aftermarket rebuilt engine.Would not run correctly.After basic tests,found 0 compresion in # 3 and # 4.<br />Rebuilder had me pull the head and look for damage.None visible.Machine shop says the head is not the problem.Cylinders look good,no scoring,just cross hatching.Put carb cleaner around pistons,it didn't run down past the rings.Gaskets look to be not the problem.<br /><br />Have another engine comming,and wonder about the problem with the first.Could the head have been 'over-planed'? Aside from cc'ing it,how can I tell.<br /><br />DHP<br /><br />PS: valves are 'adjustable' by purchasing different length push rods.These rods have no color dye,so they are the shortest available.

 

[Bondo]

Re: 3.7 L Compression Problem

Did you pressurize the cylinders ,+ see where the air was excaping ????<br />Leak-down Test ??<br /><br />There should be a Measurement to determine the Total Thickness of the head.....<br />Maybe measuring from the Face of the head to the Flats that the valve train sits on..??<br /><br />Were any of the valve seats recessed ??<br /><br />Just Shooting in the Dark here...... I Don't do 470s........<br />Good Luck....

 

[DHPMARINE]

Re: 3.7 L Compression Problem

Thanks Bondo,<br /><br />No we did not presure test the cylinders,so all we know now is that the head is okay (good machine shop checked it).Wish we had,because I think the valves were open because the head was "over planed",and the push rods were holding them open.We did have some fuel spraying out of the carb.<br /><br />Valve seats were fine.<br /><br />Problem is the engine goes back to the rebuilder.If they say the head and block have no problems,no reimbursment.<br /><br />DHP

 

[achris]

Re: 3.7 L Compression Problem

The head would have the be SERIOUSLY planed to cause the valves to hang open, the lifters are hydraulic and should collapes to compensate. And if that was the case, why would only 2 cylinders do it and not all 4?<br /><br />I would check and see if the lifters (for the suspect cylinders) could be collaped further (from the closed position).<br /><br />Chris.........

 

[Bondo]

Re: 3.7 L Compression Problem

Does Mercruiser offer a limit on planing the head in the service manual ??<br /><br />There's Got to be a Spec on it......<br /><br />That's how it works with our diesel equipment heads.....<br />That Good Machineshop Should have access to the specs on a Big Block Ford head...???

 

[DHPMARINE]

Re: 3.7 L Compression Problem

achris<br /><br />I agree with what you say .... But these valves are only adjustable by push rod length.And the different lengths aren't that far apart.<br />I can only say what happened.The engine had no strange (mechanical) noises if that helps<br /><br />DHP

 

[DHPMARINE]

Re: 3.7 L Compression Problem

Bondo,<br /><br />Guess I am really going to finetooth all the specs I can find on these 3.7L's.<br /><br />You have me thinking.Where could you measure ... from the planed surface .... to what ? Like I said you've got me thinking.<br /><br />I am not sure if the machine shop realized it is basically a 4 cylinder big block Ford,but if they did,are there still differences ?<br /><br />DHP

 

[Bondo]

Re: 3.7 L Compression Problem

The Face of the head is a planed surface.......<br />And, So is the surface the valve trains mounts to......<br /><br />That's Also the Critical dimension that you're looking for........

 

[rodbolt]

Re: 3.7 L Compression Problem

with modern hydrualic lifters you can miss it .05 or so either way and it will run.the valve timing may be slightly off but not enough to notice. if the rebuilder installed the cam, lifters and assembled the head and block assy I wont touch them. if I determine that it has an internal problem I will document it, mark the block in an unobtrusive spot, and send it back. been involved with to many long and short block rip off joints over the years. I wont use reman engines unless I am the reman man. the MCM 3.7 is a beast to check valve clearence. after properly torquing the rocker nut you have to use a lifter collapsing tool and a special feeler gauge to measure minimum and maximum valve clearence. its not like a standard auto engine. I think there are about 5 different pushrod lengths. my guess is someone used one to long some place and a valve was open. a simple quick leakdown test would have verified what and where the leak was saving everyone many hours of work.this aint rocket science but a quick test sometimes saves hours.red is the shortest,at 8.595-8.625, no color is the next at 8.655-8.685, blue is 8.625-8.655 and yellow is 8.685-8.715. but I still think you had a valve open. do you have the lifter collapsing tool and the feeler bar set ?<br /> double check my color codes. I am looking at the merc manual but its possible its a mis print. has been known to happen. sometimes we did not get manual updates other times the admin fails to fwd them to service .its also possible that a bad or incorrect part# lifter was installed.did you check the block surface for flatness? I really dont like the open deck design but no one asked me when they made it. its also possible that the head bolts bottomed out and did not draw the head down. but usually a zero reading indicates an open valve or a hole in a piston. even with no rings on a new bore you would get a low reading. good luck but try to do as much documentation as possible. some reman places ask no questions and just send another and some willblame everyone else including the shipper and make you sue them, if they have not gone out of business and reopened with a new corprate name. I dont do enough 3.7 work anymore to remain proficient . I have to consult the manual for almost everything. lucky here in the salt pond they are all long corroded away.<br /> good luck and keep us posted on the outcome

 

[DHPMARINE]

Re: 3.7 L Compression Problem

^ ^ <br /><br /><br />DHP

 

[rodbolt]

Re: 3.7 L Compression Problem

anyword from the reman place yet ?

 

[DHPMARINE]

Re: 3.7 L Compression Problem

I'll let ya know when it happens.Won't even get another rebuilt until the end of next week,then have to find time to swap before we even send the problem motor back.<br /><br />DHP

 

[rodbolt]

Re: 3.7 L Compression Problem

my reccomendation would be to leakdown test the new motor before any assy.

 

[MrBill]

Re: 3.7 L Compression Problem

Zero compression is very odd...as others have said you would be led to believe a valve is stuck open, etc. How about timing (crank-to-cam)? Set properly? It sounds like you cranked the engine with valve covers off and checked the valve train. Does everything appear to be moving properly? Valve travel seem the same for all cylinders?<br /><br />Try removing the two rocker arms for a cyclinder, etc so you know the valves are closed and test compression one cylinder at a time...any reading? I think the problem is related to valve timing, sticking or remaining open or seating. Please let us know what the final answer is.

 

[DHPMARINE]

Re: 3.7 L Compression Problem

Just heard from the engine rebuilder.No problem with their engine that we installed,sent back to them because it ran real bad,and had zero compression on #3 and #4 cylinder.<br /><br />Took 3 more of their engines to get one that would run correct (so far)<br /><br />What do you guys think?<br /><br />Obviously not buying more of their engines.<br /><br />DHP

 

[Don S]

Re: 3.7 L Compression Problem

To be honest, I would send them all back, get your money back and forget them completely.<br />Now you have 1 out of 4 engines that works for the time being. And if it self distructs in 2 months, do you think warranty will be honored? I doubt it.<br />I've been had by more than one rebuild house, and personally will either buy brand new long blocks from either Merc or Volvo, or buy Mercs rebuilds. At least I know they will warrant what they sell, and their rebuilds are never more than a .030 bore.