Johnson V4 140 No Compression on 1. Broken/Missing Rings

[rrw]

Hi guys,
This might get long but i want to try to convey the whole story. Last year i bought an old boat for $200 with a 1979 V4 140 on it. I didn't do any work/maintenence on it, i put it on my Starcraft fishing boat, used it a few times, it ran good. I quit using it in October, put it in the shed for the winter. Took it out a few weeks ago, it fired right up and ran good but i ran it out of fuel. i filled it up and used it a week later, it fired up real nice and ran good, i ran it wide open for a few minutes (i think it was about 5400rpm) when i idled it down it sounded like crap. I shut it off, did some trolling, when i went to start it it started hard and didn't want to idle at all, i finally got it moving after a few times of dying out. It ran decent at half throttle and above.
Today i pulled the plugs and did a compression test. 3 were at 115/120 psi, the right side bottom was like 5psi at best. I pulled the head expecting a hole in piston or really bad scoring, that head was wet with oil/gas, the piston and cylinder looked really good so i pulled the side plate off, i think the lower ring is completely missing and the gap on the upper ring looks like a piece may be broke off of it as well.
Couple questions: is this super rare? What caused it? Am i really lucky the cylinder didn't get taken out? Can i simply pull that piston out re ring it, hone the hole and reassemble? Any comments/info/suggestions are appreciated. Thanks, Ryan

 

[joetheis]

First thing I'd do is find out WHERE the ring parts went?????????
I'm thinking in all the bikes and car motor I'll pulled apart, I never had the ring just "disappear", as the rung doesn't go below the bore.
Sounds like it broke, and the pieces went UP into the cylinder and out? the exhaust?
What does the head look like?
Without pics I'm thinkin you need a piston as I bet the ring grooves are bad.
You CAN just re-ring that cylinder, but you got it all apart, why not do all?
Look, find the pieces, as the lower end of motors don't like "Reeces Pieces" floating @, (seals bearings etc)
Joe

 

[Faztbullet]

Couple questions: is this super rare?

No....

What caused it?

If its all original it was the high dome pressure backed rings as in 78-79 they had problems with these coking up and rolling ring due to chitty gas and cheap oils...

Can i simply pull that piston out re ring it, hone the hole and reassemble?

You will need to pull powerhead and break it down to remove piston and if others are the high ring design you will need to replace them too. After the piston removeal you will be able to see all damage and will need to mike cylinders to see if they are within spec's. 90% of the motors I rebuild are worn pasr spec's and around ports from side thrust of piston...

 

[V153]

Appears you got somewhat lucky. Sounds like most of the debris went out the exhaust. Most times a chunk(s) of the ring(s) wind up between the piston & head. Ding the hell outa the head.

Can you turn the motor while looking through the bypass to see if the piston's chewed up? Course that'll only tell you about the section that's exposed ...

Buy a shop manual, then tear her apart. If I can rebuild one any idio ... er ... you can too!

 

[johnson89]

that old of a motor I am sure all the cyl.s are out of round.....I just did my 89 90hp and had to bore all 4cyl.s....I spent right at 1000.00 for all parts and getting block bore 20 over,doing work myself.....

 

[V153]

Sounds about right. That's around what it cost to rebuild my '86 90 while back. With rebore/new pistons. Ran like a bat outa hell for 5 years, till the water jacket around the cylinder wall eroded. Still have the pistons. 020 Wisecos. Look like they did the day we put em in. No bs.

Fwiw. Depending on condition. I'd rebuild a '79 Xflow just as soon as I'd an '89. Basically the same motor.

 

[rrw]

No Title

Thanks for all the info guys. Here's some pics. The head and the top of piston arnt beat up at all. Ill have to dig into it but really don't want to throw $1000 at it (or more). Ryan

 

[racerone]

Very, very common failure.----Have a bunch of those on racks waiting to be rebuilt.

 

[rrw]

Sounds about right. That's around what it cost to rebuild my '86 90 while back. With rebore/new pistons. Ran like a bat outa hell for 5 years, till the water jacket around the cylinder wall eroded. Still have the pistons. 020 Wisecos. Look like they did the day we put em in. No bs.

Fwiw. Depending on condition. I'd rebuild a '79 Xflow just as soon as I'd an '89. Basically the same motor.

Sorry the pics loaded sideways. I've used Wiseco pistons in dirt bikes and snow machines, I assume they'd be the best option here? Are your's the same as mine and are they for sale ;-)?

 

[emdsapmgr]

You may find some ring pics inside the exhaust cavity behind the prop. They'll accumulate there till they get blown out into the lake. Whatever pistons you decide to use for any rebuild, make sure all 4 are from the same manufacturer. Don't mix them.

 

[rrw]

Ok, ill check for pieces tomorrow. Is it likely that a good decarb could've/would've prevented this? Thanks, Ryan

 

[racerone]

No, very common failure has to do with the design of the top ring !

 

[emdsapmgr]

An occasional decarb is good PM for these crossflows. They tend to accumulate carbon around the ringsets. That is often a contributing factory to poor internal lubrication of the rings and can contribute to internal overheating with no overheat warning. Use of XD50 oil and occasional decarbs will extend the life of this engine. The delicate ringsets from the factory were designed for high compression and don't tolerate carbon, overheating at all well. The factory redesigned the pistons to move the top ring down slightly from the crown of the piston for added durablitly.

 

[V153]

Sorry the pics loaded sideways. I've used Wiseco pistons in dirt bikes and snow machines, I assume they'd be the best option here? Are your's the same as mine and are they for sale ;-)?

Sorry these are spoken for rrw. Goin in the '83 for my Carlson.

Some folks say they don't like Wiseco's but I ain't never had a problem. Just need to be patient breakin em in. Use lotsa good oil'n don't rush the process.

Fwiw I've had Wiseco's get destroyed by other things coming apart. But never had a piston or ring fail.

 

[Faztbullet]

You can get the WSM pistons cheaper than Wisecos and they are a better piston IMO .I have only had 1 WSM piston with a problem and had quite a few Wisecos fail, most lost the locating pin...

 

[JRegier]

If you don't plan on dumping money into that motor, depending on where you are I'll take it off your hands haha