Broken Piston Ring

[Nathan S]

I have a 94 Johnson Venom 200. The motor was rebuilt a little more than a year ago. It ran great until the other day. I made it to my spot and it cut out while idling and when I started it back up it began knocking and running very rough, so I cut it off and trolled back. When I got home I checked the compression and noticed one was bad and peered into the cylinder to notice a gouge in one side, which makes me think that it broke a ring. Now I am at a cross roads. Should I rebuild again? The only way I think I can afford it is to do the majority of the work myself. Since it has been rebuilt recently, would it be ok to only replace/repair the one cylinder? Or is it time to call it quits with this one and wait until I can afford something else?

 

[Dhadley]

Re: Broken Piston Ring

It costs almost nothing but time (and maybe an adult beverage oe two) to get it apart. Then a more informed decision can be made. We'll assume that it was still running, although badly, so there is no rod sticking out. If so, we might assume the block is boreable and the crank is good. Probably 5 if not 6 rods are OK too.

Let's pop it open and see where we are.

 

[emdsapmgr]

Re: Broken Piston Ring

It is acceptable to overbore just one cylinder. Oversize pistons are made to weigh the same as standards. Factory pistons come in .030 oversize. That may be enough to clean up the mark on the cylinder wall. You should not need to rejet the carb.

 

[HybridMX6]

Re: Broken Piston Ring

It is acceptable to overbore just one cylinder. Oversize pistons are made to weigh the same as standards. Factory pistons come in .030 oversize. That may be enough to clean up the mark on the cylinder wall. You should not need to rejet the carb.

Is it really? I'm at this same crossroads right now with one of my engine. Only 1 cylinder is bad, the other 2 are perfect. I was going to re-ring them only but have that top cylinder bored out and replace the piston/rings. Can others comment on that as well.

 

[Benny1963]

Re: Broken Piston Ring

d hadley is the man with those engines ,
doing one cyl would be the wa to go seeing as they are not cheap.
but if not you can always just call me and i will pick it up and junk it for ya .
LOL. good luck and welcome

 

[Dhadley]

Re: Broken Piston Ring

You can replace one piston if needed as mentioned. That is IF the other cylinders measure within spec AFTER you hone them. It really doesn't matter how good they look.

 

[James R]

Re: Broken Piston Ring

Before anything else is attempted The head or heads need to be removed and the bores carefully inspected and measured for diameter and roundness. If some or all fail to meet specs then those need to be bored. As the motor has been worked on before don't be surprised if there is not enough meat to bore again. Wiseco make pistons which are of greater oversize than the motor manufacturer supplies. A good boring shop will tell you if it is possible to bore and still fit a piston. Beyond that then re-sleaving is one option.
The question still arises how did it come to break a ring?

 

[SKEETR]

Re: Broken Piston Ring

yea, who did your rebuild only a year ago. Was it just re-ringed then? If I were you I'd save up and get the block done up right. Bore the one and oversize the piston, have the other two honed and re-ring'd. Make sure the machinist takes the time to bevel the ports. Breaking an engine down is not something you want to do yearly. I don't mind the wrenchin it is the scraping that gets me

 

[1946Zephyr]

Re: Broken Piston Ring

Reboring only one cylinder? Hmmmmm. I never thought of that. Is that a good idea? Won't that create un-even compression between cylinders?

 

[Benny1963]

Re: Broken Piston Ring

you need to disassemble and take block to marine machine shop let them
mic it up and tell ya what all your cyls are at and go from threre
boreing one hole doesnt effect compression the machine shop will let ya know what to go with, i usually get my piston and rings from them they will give you a bore thats correct for application ,boreing one or two doesnt hurt at all
the oversize piston weighs the same as the others .
ive built three now v6s useing manual machine shop and a lot of help from the guys on here in the end if you take your time you can do it ,
and the cost well lets say you cant replace it for the money .and you will know its right and will know a lot more when finished

 

[emdsapmgr]

Re: Broken Piston Ring

Referring to James R's comment. If you have round and like new cylinder walls, a single hole overbore and honing of the other 5 will not make any difference to the engine. If you have tons of hours and the other 5 bores are tapered or oval-shaped, then you can wind up with differences between the overbore hole and the other 5 after the overhaul. Let a machine shop check it out before you decide what to do.

 

[HybridMX6]

Re: Broken Piston Ring

I know it's not my thread, but the comments are all much appreciated. I have one cylinder that needs to be bored (it's pretty badly grooved), the other 2 I will have to get the shop to mic for me and see how it looks. This is making me consider rebuilding it a lot more now since I know it could cost up to $250 less since I may not need all 3 pistons, just 1 and 3 sets of rings (one oversize of course).
Thanks

 

[Nathan S]

Re: Broken Piston Ring

I took the heads off and looked. I did not do the first rebuild. All the cylinders have been re-sleeved. The one that I believe broke a ring has a nice gouge that doesnt appear to be deeper than the sleeve. The piston has a chip in it. And the head has marks in it from broken metal pieces. Hopefully soon I will get it further apart and do some more investigating. But can one only one cylinder be re-sleeved without damaging the others? Also does the cover need to be replaced? I will try to get some pics, but now my computer is acting up! Nathan

 

[Benny1963]

Re: Broken Piston Ring

yes you can sleeve one hole put new ring in others and new piston in bad hole you will want to inspect bearings on tear down

 

[Dhadley]

Re: Broken Piston Ring

I doubt all 6 cylinders were resleeved, that's getting pretty expensive. You can find another block cheaper. Nothing can be determined until you get the powerhead apart and have it all measured. Most likely you'll need to replace the head but again, no big deal.

 

[fixmyevinrude]

Re: Broken Piston Ring

I also had a similar problem with similar symtoms. I had a deep gouge in the side of the cylinder. It turns out it was the piston ring pin. It broke loose from the ring groove and let a deep gouge in the side of the cylinder. I am 80 percent finished with the rebuild. Just waiting for a few more warm days to complete putting all the wiring etc. back on the motor. This apparently is a common problem on this generation of OMC outboards. My motor is a 94 200 Evinrude. I would think it may be very similar if not exactly the same motor. If I can help you let me know.

 

[Dhadley]

Re: Broken Piston Ring

The bottom locating pin is lined up with a finger port on the 93 & newer 90* V6 loopers. If the combustion temps get too high the pin will become loose (as with any motor that has ring locating pins). When the pin gets loose it will try to get into the finger port. Sometimes it does and sometimes it gets beat back into the piston. In either case the rings will then rotate.

Wiseco moved the lower locating pin on their 93 & newer pistons. OMC never did and I don't believe BRP has either.

 

[HybridMX6]

Re: Broken Piston Ring

So, would it be wiser to go with the Wiseco pistons? Ad does that same info apply to a 1993 60hp 3cyl?

 

[Dhadley]

Re: Broken Piston Ring

I prefer the Wiseco's in anything I have because they're forged but that's just my personal preferance. I have no problem with OE pistons except in a few cases. The 90* looper is one motor that I wouldn't run the OE piston without making darn sure the combustion temps are right.

The 3 cylinder motors don't have pins that line up with a hole.

 

[HybridMX6]

Re: Broken Piston Ring

Hmm, interesting info. Something I will keep in mind. I don't suppose you happen to know the approx. price diff. between OE and Wiseco do ya?
Thanks.