115ETL78C cyl #1 detonation, twice??

ewcowboy

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Bought the motor with a bad cyl #1. Went through whole motor, carbs and all, started right up after rebuild, 25 hours later detonation on same cyl on same spot on the piston. Any ideas? Thx Eliot
 

iwombat

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Re: 115ETL78C cyl #1 detonation, twice??

Bad water deflectors on that bank?
 

ewcowboy

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Re: 115ETL78C cyl #1 detonation, twice??

tHe fiberous semi round things between the cylinders in the water jacket?
 

iwombat

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Re: 115ETL78C cyl #1 detonation, twice??

They're just cut rubber lines, but yeah. They route the water around the cylinders properly. They should be replaced during a rebuild.
 

ewcowboy

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Re: 115ETL78C cyl #1 detonation, twice??

Just one per cyl correct cause they got replaced
 

petryshyn

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Re: 115ETL78C cyl #1 detonation, twice??

Did you inspect the water jackets under the covers on each head?
Did the head on that cylinder have a rough combustion surface?
 

Faztbullet

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Re: 115ETL78C cyl #1 detonation, twice??

It sounds more like a ignition problem than a cooling problem to me, like a bad pack or timer base. Index the flywheel and check timing on that cylinder and I just about bet you will find timing not steady/high on that cylinder.
 

kenmyfam

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Re: 115ETL78C cyl #1 detonation, twice??

Got any photos ??
Did you check the head temps after re-build ?? Is that cylinder running lean ??
Just a couple of thoughts.
 

ewcowboy

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Re: 115ETL78C cyl #1 detonation, twice??

The cooling chambers had a little bit of corrosion but nothing out if the ordinary. Head temps were cool across the board. One other thing I forgot to mention is I blew the head gasket on thar side between completion of the last rebuild and the my current detonated piston. I've got it all torn down already and parts on the way gor tomorrow. I'll throw er back together and check timing. It just boggles me that it detonated in the exact same spot on that cyl, oh and there is a very small crack in the sleeve in the center of the hot spot. Sleeve deep by 2-3 mm. I'll try and get some pics on tonight. Thanks guys got the responses Eliot
 

emdsapmgr

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Re: 115ETL78C cyl #1 detonation, twice??

Did you do an autopsy on the portion of the carb that feeds that #1 cyl? If that cyl runs lean it will cook the piston quickly. If you have any debris in any of the jets, it will restrict fuel/oil flow to that cyl. You need to carefully inspect that carb to insure it flows fuel through all the carb passages to #1 in order to eliminate fuel flow as a contributor to your current failure. Cracked sleeves are usually a condemning factor when determining whether to reuse the block. Depending on your pictures you post, you may need to get that cyl resleeved.
 

kenmyfam

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Re: 115ETL78C cyl #1 detonation, twice??

oh and there is a very small crack in the sleeve in the center of the hot spot. Sleeve deep by 2-3 mm.

I think you just may have answered your own original question.
 

mikesea

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Re: 115ETL78C cyl #1 detonation, twice??

sleeve should not have cracks or "hotspots"you likely have some kind of flaw at that point and normal heat temps may put it out of round worse than cold,you should alwys bore the cylinder after it blows to get to spec.I never rebuilt a powehead without boring to next oversize an putting new piston kits in,you need to check for cracks between ports also.minute cracks are a catch for rings
 

iwombat

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Re: 115ETL78C cyl #1 detonation, twice??

This is also why it's said time and again. Figure out why it failed first, then rebuild. It's an expensive lesson if you have to learn it the hard way.
 

ewcowboy

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Jun 29, 2009
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Re: 115ETL78C cyl #1 detonation, twice??

Thanks for all the replys guys bit 115 is going on the back burner. Got a 81 evinrude 235! Mucho faster!!
 
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