gonna troubleshoot a motor KNOCK..need some help

[bob johnson]

I have a 1997 90 hp Ocean Pro...

was told it had a knock before I bought it...but after hearing all the trips it made with the knock I was gambling it was going to be something minor..

I mounted it and ran it...but the knock was a little more that wanted to hear...it ran great...but since i was going to use it in the winter...i needed to trust it..

the knock didnt sound deep and loud...sounded like it was under the flywheel..

anyway, i got another motor.. and have used this 90 for parts in a pinch here and there.

but now i was to tear it down and fix it and have it ready for a back up


I have popped the heads and have the LU off and dissasembled

what tests can i do to "check" for this knock...if I was to assume it was in the crank-rods area...???

and as i dissasemble this baby, what am i looking for to check for this KNOCK..i was hearing???

I am assuming any serious knock would be in the crank and rods-piston relationships...

but is there any other area???

I need to read my manual tomorrow hopfully finding a way to take the flywheel cover off to expose the flywheel nut so i can rotate this motor and do some checks.

it has the OIS ignition system and as such the flywheel is totally covered

I have two months to do this project..I now have the motor in my lighted shed...so i can work on it nights...

thanks


bob

 

[tmcalavy]

Re: gonna troubleshoot a motor KNOCK..need some help

Spin the motor/flywheel and listen until you find the knock, then go inside cautiously. You can use an impact driver or heavy duty drill with socket to turn the motor over.

 

[Faztbullet]

Re: gonna troubleshoot a motor KNOCK..need some help

Most likely going to find a rod bearing,center main or cracked piston skirt as this is what I see in most of the 60 degree failures.

 

[mikesea]

Re: gonna troubleshoot a motor KNOCK..need some help

as you tear it down,it will be obvious,

 

[bob johnson]

Re: gonna troubleshoot a motor KNOCK..need some help

most likely one of the things already mentioned.

what really makes me wonder is the amount of running time since the knock has been noticed.

a little history...this guy boat a boat he really loved, but the seller told him the motor had a knock.

he bought it any way...he ran in LI Sound...he said he went out about 12 times to the RACE..thats about an hour out from his mooring.

factor in all the hours on the motor while out there...thats a lot of hours on the motor... but the knock was always there...his wife was worried because it can get nasty out there in THE RACE, lots of current ..she didnt want to get stuck,

she made him go buy a new motor.

but written on the OIS cover you could still see the word KNOCK....so the knock has been there a while.

that was why i took a chance on the motor..i figured it couldnt be a rod or crank because it wouldnt have lasted so long

anyway thats the history...hopefully ill find whats wrong...

be positve about it and solve it..

but I figured id ask, in case there is a slight possiblility it is some other sourse and need to inspect that area carefully before i continue on the teardown and all my evidence is gone!!

the heads have been off before...the pistons are not marked over size..

the covers all have well worn screw slots!!! = meaning they all have been removed a LOT OF TIMES!!!

the power packs were made in 2004...so they have been replaced...

thats all i know so far..

wish me luck


bob

 

[boobie]

Re: gonna troubleshoot a motor KNOCK..need some help

I always ask dumb questions. What did the g/c oil look like and were there any metal shaveings in it ? Sound travels.

 

[Fl_Richard]

Re: gonna troubleshoot a motor KNOCK..need some help

as you tear it down,it will be obvious,

Well stated.

When you get to the offending bearing or sleeve you'll notice this one isnt like the others. That's the bad one(s). If the damage is light it will be darker or obviously worn unlike the others. The tolerances that begin to knock are small. Unless it was coming apart you may not see metal flakes or shavings.

 

[bob johnson]

Re: gonna troubleshoot a motor KNOCK..need some help

I always ask dumb questions. What did the g/c oil look like and were there any metal shaveings in it ? Sound travels.

I took the lower unit off didnt have any shavings come out...oil was just a little milky and then all pure oil...seemed ok to me...

installed a new water pump.

I installed the lower unit on another motor and am running it now..KNOCK didnt follow along luckily!!!!!!!

and am rebuilding the LU that will go onto the motor the Post is about...


bob

 

[bob johnson]

Re: gonna troubleshoot a motor KNOCK..need some help

so the next step right now is to start removing the trigger-timer of the OIS system off the top of the motor..

any tips on what to make really sure I know how it goes back together???

anything that is tricky??

whats the most important part of taking all these parts off...and knowing how they go bak together??? pictures?? there seems to be a myriad of adjustemtns on all these compnents...and they all have an effect on the motors running

bob

 

[boobie]

Re: gonna troubleshoot a motor KNOCK..need some help

Bob, another dumb question, Do you have an OEM service manual ? If not you should get one. I have a 1998 manual sitting on my desk and it shows good pics and step by step instructions for anything from ignition dissassembly to power head. Glad to hear your g/c was okay. I've seen guys tear down a complete p/h for knocks and it turned out to be a bad l/u.

 

[bob johnson]

Re: gonna troubleshoot a motor KNOCK..need some help

Bob, another dumb question, Do you have an OEM service manual ? If not you should get one. I have a 1998 manual sitting on my desk and it shows good pics and step by step instructions for anything from ignition dissassembly to power head. Glad to hear your g/c was okay. I've seen guys tear down a complete p/h for knocks and it turned out to be a bad l/u.

I have maybe 7 or 8 factory manuals...

for various motor i have or have had.. and I have one for this motor as well.

I have several different brand manuals for this motor!!! and use them all more pictures the better.

thanks

bob

 

[bob johnson]

Re: gonna troubleshoot a motor KNOCK..need some help

I tore my 90 hp down a lot further today....

I have the block still on the midsection and I have just the crank, rods and pistons in it....


the crank journals are obviously still on.. I was looking in the intake area at the piston skirt and I see some galling on the skirt of one piston..

could that be the knock? of course their are four sides of pistons I cant see, so maybe there are other pistons with galling...

but from the intakes i can only see one with galling..

I tried to find play in the rods-pins-crank...but it seems solid!!!!

no free play at all.

i rotated the piston over top dead center and start it moving downward and stop...

then I try to push the piston towards the crank..to see if there is any movement available.

nothing...

so I am thinking it isnt going to be the rods...

BUT I am still going to continue with the teardown

but big stumbling block now...is that there are two bolts holding the lower case of the block onto the crank that the heads are TOTALY dissolved in rust...I will have to machine the head off ....

one other is rusted bad, but still looks like a boilt head...the others look brand spanking new!!!

go figure.....

that speaks alot for lower cowling seals!!!!!

bob

 

[Craig-]

Re: gonna troubleshoot a motor KNOCK..need some help

I tore my 90 hp down a lot further today....

I have the block still on the midsection and I have just the crank, rods and pistons in it....


the crank journals are obviously still on.. I was looking in the intake area at the piston skirt and I see some galling on the skirt of one piston..

could that be the knock? of course their are four sides of pistons I cant see, so maybe there are other pistons with galling...

but from the intakes i can only see one with galling..

I tried to find play in the rods-pins-crank...but it seems solid!!!!

no free play at all.

i rotated the piston over top dead center and start it moving downward and stop...

then I try to push the piston towards the crank..to see if there is any movement available.

nothing...

so I am thinking it isnt going to be the rods...

BUT I am still going to continue with the teardown

but big stumbling block now...is that there are two bolts holding the lower case of the block onto the crank that the heads are TOTALY dissolved in rust...I will have to machine the head off ....

one other is rusted bad, but still looks like a boilt head...the others look brand spanking new!!!

go figure.....

that speaks alot for lower cowling seals!!!!!

bob

The piston skirt is usually the first thing to break. Check the cylinder bore of the one with the scored piston. If it is out of round, the wrist pin bore may be stretched, causing the piston to rock.

Are you sure the knock is in the powerhead? There can be a lot of prop slop, which bangs back and forth on sudden deceleration and might sound like a rod knock.

 

[bob johnson]

Re: gonna troubleshoot a motor KNOCK..need some help

The piston skirt is usually the first thing to break. Check the cylinder bore of the one with the scored piston. If it is out of round, the wrist pin bore may be stretched, causing the piston to rock.

Are you sure the knock is in the powerhead? There can be a lot of prop slop, which bangs back and forth on sudden deceleration and might sound like a rod knock.

no totally not the decelleration knock.....

I had that as well and I have it in the 115 i have now.

this was a slight tapping actually, that sounded like it was coming from under the flywheel.

but once i got the motor mounted and was running it at higher than MUFFS rpms...it was obvious it could lead to problems...


it didnt sound good at all...but not enough to immediately want to shut the motor down..


since it came up through the flywheel and got louder and more serious sounding..I thought it might be in the crank-rods area..

there is no play I can recreate in the piston-to rod-crank connection...while the pistons are still in the block

piston slap seems to be the most plausible at this point...but i am continuing and will take a look at thepistons in hand.

tis weekend ill pop the block off the misection and bring it to work to cut the rusted bolts off the crank case...

bob

 

[bob johnson]

Re: gonna troubleshoot a motor KNOCK..need some help

took the block apart today....took some pictures...

all looked good excpet for one piston.

and MAYBE some rod journal end side wear...slight galling...I think that bad piston got hot a lot..is looks like it cooked the oil down inside the piston!!!

like you burn oil in a frying pan!!

this last picture is supposed to show the galling marks on the bore... they look greyish..

I think it will hone out...but i wonder what caused this piston to start galling.

is it possible it over heated at one point, and then the over heat was fixed , put the piston still slapped....but wasnt getting any worse??

or was it on its way to destruction??

best i can tell is the piston is way undersize now
actually it is way egg shaped too!! the spec is within .003" and the difference is like .015"

3.575 and 3.590

the other three measure 3.597- 3.594
give or take .001" between the different pistons.

havent checked the bore...

but I am gonna just bore them oversize and use all new pistons..

does the galling on the side of the rod journal look bad?? is that common?

bob

 

[Craig-]

Re: gonna troubleshoot a motor KNOCK..need some help

Water jackets clear?
How does crank journal look, measure?
Cylinder scored, measure?
You could re-sleeve, new piston, rod & bearings if just the one is bad or maybe get away with just a hone job, new piston, rod & bearings.

 

[Craig-]

Re: gonna troubleshoot a motor KNOCK..need some help

Is this the one you are putting the 115 parts on?

 

[bob johnson]

Re: gonna troubleshoot a motor KNOCK..need some help

Is this the one you are putting the 115 parts on?

yes...

havent measure everything yet....just measure the piston OD's quickly


I would like to know why.....this happend...

but I am gonna bore oversize and put all new pistons and rings in...

the crank looks great...there was no slop or play in the rods..

and I am thinking of reusing the rods...

as long as the pin hole mic's out ok.


the cylinders look ok...good cross hatch in most but down deep each cylinder has some lines in the bore...but they didnt translate over onto the other three pistons????


bob

 

[Craig-]

Re: gonna troubleshoot a motor KNOCK..need some help

The cause is heat from poor cooling (stopped up passage) and/or water intrusion due to bad seal and/or corrosion. I'd guess this is a salt water motor.

If just the one cylinder is affected the other pistons should be fine. That rod got real hot. Replace everything in the bad one, piston, rod, bearings and only over bore if necessary. Keeping them all the same is not necessary.

What were the comp test #'s?

 

[bob johnson]

Re: gonna troubleshoot a motor KNOCK..need some help

The cause is heat from poor cooling (stopped up passage) and/or water intrusion due to bad seal and/or corrosion. I'd guess this is a salt water motor.

If just the one cylinder is affected the other pistons should be fine. That rod got real hot. Replace everything in the bad one, piston, rod, bearings and only over bore if necessary. Keeping them all the same is not necessary.

What were the comp test #'s?

I did a comp test on the motor last feb when i bought it...they were all 120's

motor ran strong!!!! had it on the boat for a month or so....

just knocked... wasnt really that bad, but you could tell it wasnt just a simple fix...which is what i had hoped for...


you could tell it was deep and came from the rotating mass of the motor.

with all the tight specs on the pistons and bores and, then going and getting the other bores honed out..and trying to stay in spec...isnt worth it after coming all this way..

a piston with rings is under $100...so $300 more plus the boring..

makes me feel better about the motor when i put it all back together..

if you think about the time to pull the motor off a running boat and tear it down and do it all over..

spending another $500 is a bargain..

how can you be sure about the over heat??

I know thats the result....pistons out of roundness and galling...

bob