Merc 140 Low compression on 2 cyls UPDATE 08/12/04

[doman]

86 mercruiser 140 ..Boat has been sitting at least 6 months while i was restoring the interior and at least 2 years prior to that...cyl #1 150 cyl #2 75 cyl #3 100 cyl #4 150 ..I just spend little over $1000 on the engine work everything is new except the internals wasnt expecting that compression will be low ...after we fire it up it misses at idle sometimes it runs fine at higher rpms ...<br />Turns out compression is low on 2 middle cylinders but its starne that only 2 middle are low and the other two are fine...Now would should i do ? run it and see if the compression will come back ? or rebuild it right away ...I did put some oil in to the cylinders and some carb cleaner stuff to soak them for a few days ...im hoping it will free up the rings<br />What do you guys think i should do is there anything i can add to the fuel or oil that might help..or should i just forget about it and take it appart?<br /><br />Any input is really appreciated<br /><br />Thanks<br /><br /><br />Dom

 

[Hotrods]

Re: Merc 140 Low compression on 2 cyls UPDATE 08/12/04

As I am glad I did.. pull the head and get a look see. MIne was really bad and she ran pretty good. pulled the head seen a bad ring and piston. glad I did or I could have turned her to junk

 

[doman]

Re: Merc 140 Low compression on 2 cyls UPDATE 08/12/04

i dont think it will get me anywhere if i pull the head unless the piston is fried or something which i dont think it is ...i think the rings are just stuck for sitting so long ...

 

[cobra 3.0]

Re: Merc 140 Low compression on 2 cyls UPDATE 08/12/04

Mine has piston 3 and 4 at lower readings. The engine runs fine though. Could be just the head gasket...could be the rings...could be badly adjusted or worn valves too.<br /><br />I guess if your oil and decarb don't do it, then you will have to open it up and see what's up. However, try adjusting the valves first.

 

[doman]

Re: Merc 140 Low compression on 2 cyls UPDATE 08/12/04

Valves are fine i did the wet test ...poured oil in to #2 and #3 and it went up over 150psi ..so valves are holding just fine ....i guess ill just take it out few times see what happens if compression doesnt come back ill pull it out over the winter and replace the internals coz its basicly the only thing left to replace everything else is new

 

[cobra 3.0]

Re: Merc 140 Low compression on 2 cyls UPDATE 08/12/04

You seem to know where you are heading with it. Good luck with your test run! Let us know how it goes.

 

[TooTired]

Re: Merc 140 Low compression on 2 cyls UPDATE 08/12/04

Valves in the 140 merc are adjustable?? If so how do you adjust them?...mine may need done.Its also a 1986 motor

 

[cobra 3.0]

Re: Merc 140 Low compression on 2 cyls UPDATE 08/12/04

TooTired, I cut and paste this following recommendation from another fellow on the forum...I forget who...but here's what he said:<br /><br /><br />"The valve lash needs to be set for each rocker arm so that you don't run the risk of bending a pushrod by tightening the nut too much.<br /><br />Watch your rotor with the cap off and crank the engine until the rotor stops where cyl. #1 would be. This is TDC for cyl. #1. You can then tighten #1 intake and exhaust, #2 intake, #3 exhaust, and #4 intake. Tighten each nut slowly while you feel for side to side play on the pushrod. When you feel the play disappear, tighten the nut 1 more full turn.<br /><br />Now crank the engine until the rotor is on #4 and tighten the three remaining rocker nuts the same way.<br /><br />I use perfect seal to seal the threads on my head bolts, I think Permatex makes something similar."<br /><br /><br />That was for my 1986 OMC 3.0. I think it's basically the same engine. In any case, it worked well with mine.

 

[calwldlif]

Re: Merc 140 Low compression on 2 cyls UPDATE 08/12/04

The valve lashing you described<br />is for hydrolic lifters. 1 full turn is max<br /><br />doman Does your motor have hydrolic lifters?

 

[doman]

Re: Merc 140 Low compression on 2 cyls UPDATE 08/12/04

WildLife i im not sure but i think yes ..hydrolic lifters...after the engine was started the first time after the long break i had some lifter noise but it went away after pressure builded up..im not sure if its realated to the low compression issue ..if so let me know what do i need to check<br /><br /><br />Dom

 

[calwldlif]

Re: Merc 140 Low compression on 2 cyls UPDATE 08/12/04

I am confused as to what your concern about the valves is. Some "tapping" of lifters could be many things. if they quiet quicky at idle, I <br />wouldn't worry. Thin oil, leak down of a lifter<br />over a few days does happen. if they pump up<br />thats the main thing. I thought your orig prob<br />was low compression, readin your testing showed<br />a ring problem. Could be stuck, worn,or broken, any of these are far worse than a intermitent tap.<br />If some "Marvel Mystery Oil" doesn't free the rings,(I love that stuff)then pull head check for<br />scoring, excessive wear at the top of the cylinder where the rings expand, or general condition of cylinder.<br />Be advised that a new head gasket at least will be required if you pull the head, torque wrench<br />intake exhaust gaskets, sealer, ect.<br />The head pulling will only allow inspection, so be prepared to have to pull motor and rebuild<br />if you find scoring excessive wear ect.<br />I don't know what prompted your compression check but, not much can be done short of soaking rings<br />in the cylinder with head on. if they don't free up then a ring job is in order.Running it untill she dies then rebuilding in an option, some good mechanics have "scopes" that can check the cylinder without pulling the head. I feel after reading the tests you have done it is a ring problem. Hopefully the rings are just stuck and some soaking and running motor with some cleaner products will free them up. A boken one would require a repair, check part avail, possible rebore with o-size new piston. It is a subjective call, worst case--- broken ring tears up cylinder<br />mandating a rebore and o-sized piston, if avail?<br />Then have to decide if doing whole motor is best course. rings, pistons? main and journal bearings<br />cam, chain, valve job,ect ect ect.<br />I vote for MMO and stuff like Sea Foam, run on the "hose" with constant re compression testing to see if it improves.<br />Then decide what the motor is worth to you.<br />Only you know the hours on the motor and the possiblity of needing a rebuild.<br />It is a tough call, many have gone through it,,<br />I know I have and will again.<br />Good luck

 

[doman]

Re: Merc 140 Low compression on 2 cyls UPDATE 08/12/04

I did put decarb in to the cylinders ..boat been sitting for 4 days ...just start it up today and guess what it doesnt miss at ide anymore engine is really quiet no taping noise nothing ..havnt checked compression coz i dont have a tool here at home ...but if its running fine i dont even wanna check it because if its stil low it will upset me even more ..<br />Btw i did buy the mystery oil today it says you can put it in gas , oil pretty much anywhere...i did pull the plugs out once again put a little of it in each cylinder plugs back in a started her up..sounds like its running much better now<br />Now should i fill the cylinders with the mystery oil once more and let it sit for few more days?<br />I dont think broken ring is an issue either just frozen or jut worn out but if they were worn out i dont think compresion on two other cyls would be 150....like i said boat has been sitting long long time ..at least 2.5 years..<br />If the ring is broken can you actually hear it?<br /><br />Dom