Piston broke

sly_karma

Crew Member
First outing of the year recently. Not enough power to plane. Back to shop, checked a few things, noticed a cracked coil housing. Replaced that. Now engine won't turn over fast enough to start despite fully charged battery, booster cable bypass of all connections, switched in spare starter motor. Removed plugs, uh oh. #1 cylinder has its electrode bent, something smacked it. Flashlight shows a slight chip on the piston, engine doesn't turn very quickly even with plugs out. I think my 1980 Johnson has run its last. I'll check compression this weekend and decide what to do from there. I suspect the damage is in bottom end. Not sure if it's worth doing a powerhead replacement.
 
She's 37 years old.
Those old looper's were good motors but it's likely done.
Actually that series was a crossflow, loopers were later, they came with the first VRO systems in c. 1985
 
I bought it as a project 5 years ago for $1000 - hull, motor, trailer. Hull looked minty, engine was old. Thought at the time I'd re-power right away. But the old girl fired up and needed not many dollars to get everything shipshape. Meantime, that pristine hull actually had lots of ugliness going on below its somewhat rotten deck. It was all back to front from what I expected. That engine ran like a locomotive until very recently, took us on numerous great camping trips into the inlets off the Salish Sea and sped me around the Okanagan to boot.
 
Compression test confirms what I figured. 55 psi on the suspect cylinder, 125-130 on the rest.

I'm toying with doing this myself. Cash is tight right now while I recover from a business hiccup back in the winter. Anyone done a powerhead rebuild on an old crossflow? Am I mad? I'd describe my mechanical skills as mid-level, but I know how to ask questions, research answers and read my shop manual. I've got a nice well lit shop and an engine hoist.
 
Havnt done that particular engine but they are for the most part nice light clean bench work. I like working on them!
It all depends what it needs. If you get into crank or bearings go another route Imo. Probably $1500 cdn for rebuilt power head. Wiseco pistons w rings and pins $114 us ea.
 
I did a 1986 150 Johnson not long ago. My advise is dont order a single part until you tear it apart and see what is going on. If bolts start snapping or the powerhead just wont come apart, move on. If the crank is damaged, move on. If the pistons are .030 or .044" oversize already, move on. Its very important to figure out why it failed in the first place, otherwise you could spend all this time and money and it may happen again. Did it go lean, break a ring, overheat, water ingestion, etc.... you need to figure that out. These engines and pretty simple and reliable and will run forever if taken care of. They do like their fuel. lol
 
Thanks for the above two posts. Mystified as to why it failed. Engine started and ran fine, water stream at exhaust fine. But away from the dock it couldn't make enough power to plane. Posts near the end of the 150 rebuild thread make me wonder I was overpropped, would just make 5000 rpm/40 mph at WOT.

Good advice re tearing it down further before deciding course of action. I'd like to rebuild if it's feasible, the engine is a good fit for this hull and is easy to work on. But it may not be sensible, rebuild kit alone costs around $1000 Canadian, plus costs of boring, honing.
 
SOme jet a little bit plugged... leaned out.
Was there some time between runs? Had inline 6 Merc toasted top cyl. Crap in top carb. Find the problem and maby nothing wrong stuffing a good used piston with some hone but that year you need to feel you can justify spending the time on it because you want to do at least rings on all. Could be just a blown head gasket and easy lol, pull apart and take a look!
 
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What engine is it? 5000rpm sounds fine at wot. Sounds like it was down a cylinder. Was it running rough or vibrating more than usual? The more cylinders the harder to tell if is done a cylinder at idle.
 
Tear it down and see if it is just a piston jammed in the hole. If no other damage it would be a cheap rebuild. Cheaper than any other option available to you...plus you will be sure of what you have with this engine when done. The only other way to be that sure is to buy new. Just take your time and use lots of heat on any bolts that are salted in tight. Better to slowly work it free then to break it off and then have to extract.
 
Just take your time and use lots of heat on any bolts that are salted in tight. Better to slowly work it free then to break it off and then have to extract.

No truer words have ever been said. The next advise goes along with that. Tighten the new bolts up to within a quarter turn of snapping, never more and sometimes even less.

Oly
 
SOme jet a little bit plugged... leaned out.
Was there some time between runs? Had inline 6 Merc toasted top cyl. Crap in top carb. Find the problem and maby nothing wrong stuffing a good used piston with some hone but that year you need to feel you can justify spending the time on it because you want to do at least rings on all. Could be just a blown head gasket and easy lol, pull apart and take a look!
I rebuilt the carbs back in early winter, this was the first run since then.
 
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