79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

[ceddon46]

THis is a new piston about 8 hours operation can any one tell me what might have caused this ?

 

[keefallan]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

What does the inside of your head look like? Does it have nicks in it like that? It looks like a ring broke and had a party in there. There are 3 possible answers: detonation(doesn't look likely) from bad gas or timing, broken ring or a broken reed plate. When you tear it down you'll SEE right away what happened. Sorry it happened to you.

 

[ceddon46]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

Yes head on that side looks the same as the piston both looks like acid was poured on them and this is on exhaust side of piston Could detonation do anything like this never seen before , just wish there would have been metal in cylinder then answer would have been easy , well weird thing is cylinders walls are perfect , but that is a good thing !!!

 

[keefallan]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

Then, you probably broke a ring. You are blessed that the walls are clear then. Still gotta break it down though......pain.:facepalm::facepalm:

Maybe there was a screw or nut(dunno) that got loose. I think you'll find a broken ring. But if you don't a piece of metal got in there somehow and played plinko and then exited stage right out the exhaust.

 

[boobie]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

When the piston was replaced, were the ports in the cylinder chamfered to take the sharp edges off of them ??

 

[Bosunsmate]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

Undo your bypass cover for that cylinder and have a look, your rings will be broken if its the bearings too but you might see a bearing embedded in the piston side,
im picking bearings failure
Seems to happen on that starboard bottom much more often than others, normally its the rings, it just looks like some of the dents a bearing shaped

 

[Bosunsmate]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

Have a close look at the head too for embedded bearing bits, generally they are darker looking than rings.

Poor water flow can cause this. The last one of these i worked on the guy told me he use to wait about 25secs for water to come out of the telltale after he had started her up. No wonder she conked less than 3 minutes from base.
After i put in a new impeller waterflow came out in less than 3 seconds.
That same cylinder on his blew its rings

 

[emdsapmgr]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

Looks like the walls in the coolant chamber are separating. Like the paint inside the water passages is coming off/delaminating in a sheet. Does not look normal. I've attached a pic of what a normal block should look like. Possible that this separation is restricting water flow around that cyl. While the rubber water deflector at the top of the pic is correctly positioned, it does seem a little close to the far right hand part of the block-narrowing/restricting the passage. You'll want to pull the carb apart, exp that carb side that feeds that bad cyl. Possible fuel restriction in the main jet that feeds that cyl. Have a look. Could be running lean.

 

[daselbee]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

I'm with EMD....that rubber water deflector at 1 o'clock position is restricting water flow.

 

[ceddon46]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

Yes I honed the cylinder out and made sure no sharp edges , carbs were rebuilt and they have good fuel flow to all cylinders , will check water flow seemed to run a little hotter after rebuild on this side just by touching it ... have not had a chance to tear it down any more as of yet , but I am kind of concerned as to this being the second piston that has had major failure in that same cylinder question could the reeds have anything to do with a lean problem since carbs are putting good fuel to that cylinder ?

 

[ceddon46]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

Yes I honed the cylinder out and made sure no sharp edges , carbs were rebuilt and they have good fuel flow to all cylinders , will check water flow seemed to run a little hotter after rebuild on this side just by touching it ... have not had a chance to tear it down any more as of yet , but I am kind of concerned as to this being the second piston that has had major failure in that same cylinder question could the reeds have anything to do with a lean problem since carbs are putting good fuel to that cylinder ? Boobie what is chamfered ?

 

[ceddon46]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

The bottom rubber should it even be there seems to me like water hits a dead end down at botton of cylinder with no path back ?

 

[ceddon46]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

this is what happened first time then 8 hours after operation this one we are discussing now , I cleaned cylinder wall up real good ... but something is causing falure only in this cylinder and on exhaust side both times

 

[ceddon46]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

And am I not correct in saying its not a lean condition based on color of piston piston only about 8 hours and it has a even coat of dark brown color

 

[emdsapmgr]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

The ring broke because it got hot. That can be because it had too much timing, too little fuel or had insufficient cooling. You need to determine just which failure mode caused this. If the main jet that feeds this cyl was restriced of the wrong size, it may have run hot due to lack of cooling fuel. (lean) Unlikely it was a spark advance issue, as all of the pistons would show similar distress. If the cooling around that cyl was restriced, it could have caused that failure on that cyl only, and may not even have set off a hot horn. Again, those cyl walls outside the cyl liner look pretty horrible. There is some sheet/crust inside there that is not normal.

 

[ceddon46]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

What would be best way to clean those passages up , and after I clean them up should I repaint them and any special paint for this ? been trying to find a block only just in case this one is fried when I get deeper in it any suggestions were I might find one ?

 

[emdsapmgr]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

I'm not sure just what that coating appears to be in the coolant walls. Could be the original paint which got overheated and is peeling. I'd think you could scrape some of it off with a long, slender screwdriver. It's serving no purpose now, just taking up space in the coolant passages. Not sure that repainting them will serve much purpose if you run in freshwater. I could see repainting if it were a saltwater engine. Don't give up on that block yet. To you, it's a "known" entity. A different block may just bring new problems. If the bad hole is a standard size, you still may be able to hone just that one cylinder liner. If significantly scratched, you can overbore just that one hole and get just one oversize piston. A common practice. Have you been into the carb main jets yet?

 

[ceddon46]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

Yes it fresh water so I will just clean passage up some, Yes I have been through both carbs rebuilds they are spotless inside , I already honed it from the first piston failure so probably have to bore it this time if not to bad..

 

[ceddon46]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

Feeling the cylinder wall with fingers it just does not feel right kinda like a dip between 2 of the exhaust port's that are cut into side of the cylinder wall , going to tear down this weekend will advise what I find ..

 

[James R]

Re: 79 johnson 100TLR79S 100 HP lost compression and this is piston help ?

Be sure to replace the deflectors with new and check that all waterways are clear. Often ignored.