1994 DT150 w/low compression on bottom starboard side cyl.

[lanier]

I have a 1994 DT150 EFI outboard that I have owned for @ 7 years and has run fine with no problems other than bad cdi which went out @ 4 years ago.

The other day I was going fishing, so the day before I ran the motor and it was running rough. I ran some seafoam through and seemed to run better, so I took it to the lake and it started misfiring, when I got home I did the compression test and all the cyl's were @115 psi except the lower starboard which was @95 psi. I removed the cyl. head and the bore was clean with no scuffs and top of piston was ok.

My question is can i remove the cyl jug off the motor and deglaze the cyl., re ring and reinstall with out taking the power head off and disassembling?

if there are any tricks to this I would appreciate any help you give.

[aquamort]

Hi mate, did you try putting a bit of oil down the spark plug hole and trying another compression test first?

Was it only missing under load? If so maybe an electronics problem ie plug lead? Im not sure your compression difference would cause your motor to misfire terribly...

[lanier]

Lower Starboard cyl. 20 psi lower than other cyl's.

The motor could use new plugs, but when I checked the compression and the lower starboard cyl. was 20 psi less than all of the other cyl's that makes me want to correct the imbalanced compression. Is this a common thing with lower starboard cyl.? Is there more to it than just re-ringing, something else going on that any of you guys know? if so let me know, because I don't want to put a small band-aid on a gaping wound if you know what I mean. I really don't have a lot of money to spend on a complete rebuild and if re-ringing the motor will give me a few more years to run I'm fine with that.

[aquamort]

putting a bit of oil down a plug hole and seeing if your compression goes up is a fair indication of what your rings are like. When you say misfire what do you mean? Is it a harsh distinct miss or all over the place if that makes sense? As i said earlier im not sure that difference in compression would cause a huge misfire. Ive had motor with terrible scoring in one pot run just fine.

Personally i would be eliminating things like ignition and fuel first. Then look further if you have to. Let us now how you go

[lanier]

Ok the fuel is eliminated because I always put stabilizer in fuel if it sits during winter months and I only run premium 93 octane non-ethanol fuel and this time I even put octane booster additive.

I'll order head gaskets and new set of spark plugs and see what happens. If it still misfires I will put oil in cyl. and check compression

just in case compression improves allot with the oil in cyl. will I be able to remove cylinder block and de-glaze, put new rings on pistons, and re install cylinder block onto powerhead without taking powerhead off of motor [can I re-ring with powerhead still on motor]

[aquamort]

Sounds like your doing all the right things re your fuel but a fuel problem could be anything from a bad injector, a bad sensor, regulator, water in fuel, etc. Can you describe the misfire at all? ie: at idle, under load, all the time, is it a distinct miss or is it erratic like a splutter?

Does it miss at idle? If so try removing a plug lead at a time to see how much of a difference it makes. The one that makes no or little difference is the culprit.

Dont forget to check plug leads with a multimeter...4k ohm per foot if i remember correctly.

I think im confused as to what you are calling a powerhead? I call the block/engine the power head which sits on the sandwich plate or engine holder. In any case if your rebuilding an engine you would want to replace crankshaft seals and gaskets while your at it.

[lanier]

Sorry for the confusion I am calling the power head the complete unit/motor, what I'm calling the cylinder block is unit that has all the bores for the pistons and in my case I have a port cylinder block and starboard cylinder block. if possible I don't want to remove the power head just the cylinder block to re-ring. I would carefully remove the cylinder block leaving the piston and the connector rod attached to the crankshaft of power head re-ring pistons, de-glaze cylinder bores, install homemade machined guide rods into threaded holes where cylinder block fastens to power head to help hold and align cylinder block, put new gasket onto guide rods and slide it up to power head , slowly slide cylinder block toward power head leaving enough room so I can compress rings and slide the piston into the bore one at a time until I had all three pistons inserted each bore. Is this possible? kind of like rebuilding/refreshing the top end of the motor like people do with motorcycles

[aquamort]

Ok. Normally Powerhead is referred to the engine that sits on top but I know what your talking about now. But *** that seems like a hard way of putting rings in!! Im sure it would be quicker to just pull the powerhead off. As i said previously you can then replace crank seals etc.

AND im still not convinced thats your problem. You still havent described the type of "Misfire". Good luck.

[lanier]

Thanks, I will buy new plugs and a head gasket, see what it runs like. I want to keep it simple and don't want to spend extra money on re-ringing if that's not need.

Thank you for your help I'll get back with the results, though it might take a while. I just got project ahead of this one to finish

[seaox230c]

Simply no...there is no "jug" to remove...you can remove the entire side cyls 1-3-5 or 2-4 -6 since each bank is interconnected by the same block they are all the same cyl head on each side...if one is bad the entire cyl assy must be removed... since you have no valves..a bad compression must come from the rings on that cyl...or a bad headgasket...since its already off...its 50 bucks for a new head gasket..try it before a rebuild

[lanier]

Thanks for the reply. Sorry for the confusion,but that was what I meant by removing cyl. block [that is what my SELOC manual called it]. I was going to take the whole side loose which had the bores for all 3 pistons on starboard side de-glaze all 3 bores inspect all of the pistons for wear/damage re-ring and assemble with new gaskets without taking anything else apart. I think this is possible, just wanted to see if anyone has done it before and if it was worth the aggravation or not.

I am going to buy a new head gasket and set of spark plugs and put cyl. head back on motor to see if the compresion is better and the skip is gone before go any further, like you said it's only fifty bucks.

Any other tips/help is appreciated

[seaox230c]

Its almost impossible to slide the pistons into the cyl head while they are still attached to the crank...you could try it... you would need 3 ring compressors...don't know if they would fit between the crank and the removed head on the bottom of the pistons..also the cyl head is boron impregnated so not much to do up there..very hard..also you would need several people...some to align the pistons and some to accurately hold the head...95 psi isn't too far off from the rest...to do a compression test accurately the motor should be warm and your throttle must be wide open..keep all your other plug holes open except the test cyl and crank the engine through 3 or 4 turns...maybe 5 or 5 seconds worth see if that helps

[lanier]

Thanks , you kind of put the task in perspective for me. when I checked the compression I did let the motor warm up, removed spark plugs out of all the cylinders, and removed the throttle linkage so I could open the butterfly all the way. I did turn it over for a few revolutions on each cylinder, but not for five seconds, more like 2-3 seconds.

On the cylinder bore, are you saying that it's boron impregnated?
If so then I can't de-glaze the cylinder wall, just re-ring?

how far can the compression differ, what I have now is @ 17% or @ 20 psi difference?

Thank you for your help