Johnson 150 Detonation

[schofy123]

I have a 1986 Johnson 150 on a 19' Grady White. The motor has been well maintained, and never left me stranded until now. I was up on plain running 4000 RPM. Motor was running fine, when I heard a high pitch noise from the motor. Shut motor off, and smoke was coming from the cowling. The right head was hot enough to melt the top two coils. Left head was not hot. I took the rt head off, and top two pistons looked like they had been sand blasted. Bottom cylinder was fine, and moist with oil. Took head to mechanic, and he said it was detonation, and motor would need rebuilding for $2,500. Hear is my question. Should I spend money on this motor or look for a good used motor? I checked diverter plate, and there was no pluggage. Thermostats were drilled out long ago. Only run in warm water. Any idea what caused this? All recommendations welcome. Sorry so long.

[DoferGofer]

Hmmn, My guess would be;
1. Drilled thermostats caused engine to run to cool, causing carbon build up.
2. Excess carbon build up causes hot spots in the combustion chamber.
3. Hot spots in the combustion chamber causes pre-ignition and detonation.
4. Engine not de-carbed often enough.

Last but not the least, I am sorry to hear about your misfortune.

PS. If it was me, I would talk to the ChampioNman about a rebuild.



Regards,

[Lockjaw]

I would try to upgrade to a 60 degree 150 if it was me.

[Lockjaw]

Here is one that might save you some money.

http://cgi.ebay.com/ebaymotors...ZWDVW

[luvdmymerc]

If the mechanic can do it for $2500. You could probably do it yourself for about $8-900.
Like I always say sometimes.....WHEN it blows up, rebuild it yourself!!!

[schofy123]

I saw the 150GT on Ebay. Looks like a really well cared for low hours motor, but it is about 975 miles from home. That would only advance my years by 3. I would really be interested if closer to home. Schofy

[schofy123]

I have a cousin that works at a boat shop. I might be able to get him to help with the rebuild. Are new heads available or can the one that got really hot be magnefluxed and surfaced?

[schofy123]

Where is the ChampioNman located? Schofy

[ChampioNman]

South Carolina.

[schofy123]

Thanks for all the replies. Great sight. I found a really clean low hours motor at my local marina. 1997 Evinrude 150. I will let ya'll know how she runs. Schoby

[Lockjaw]

It ought to be better in every way.

[DoferGofer]

If you don't mind, what is the Power at Propellershaft According to ICOMIA 28-83 rating for your engine?
My old cross flow is 106.0 kW at 5000 RPM. Just curious to know how much has changed in 11 years, ('85 to '96).



Regards,

[Lockjaw]

According to the owners manual that comes with my engine, its 112KW at 5k, however, as you should expect, mine is not stock.

I would put it at 112.00001. HAHAHA

Actually there is a little truth to that. I just put the larger bore 175 carbs on mine. Going to change the reed cages out to ficht ones, and see what that does. Its supposed to help, especially the idle. I also have Boyesens from my old GT175, and all that is the same, so we shall see which does better.

I will say this, one of these engines makes gas compared to a flow.

[DoferGofer]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Lockjaw &raquo;</TD></TR><TR><TD CLASS="quote">According to the owners manual that comes with my engine, its 112KW at 5k, however, as you should expect, mine is not stock.

I would put it at 112.00001. HAHAHA

Actually there is a little truth to that. I just put the larger bore 175 carbs on mine. Going to change the reed cages out to ficht ones, and see what that does. Its supposed to help, especially the idle. I also have Boyesens from my old GT175, and all that is the same, so we shall see which does better.

I will say this, one of these engines makes gas compared to a flow. </TD></TR></TABLE>
That is very interesting. My 1985 XP engine is 106.0 kw. Therefore, in 11 years OMC increased kw rating six points.

I think I will start paying more attention to the kw rating more than the hp rating in the future.

Best regards,



Melvin

[Lockjaw]

I am certainly no expert, but I think the change to loop charging could account for the difference.

I have a buddy who says he can port one of these engines, its very mild, but he says they make a ton more power that way, and you don't have to increase compression either.

[DoferGofer]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Lockjaw &raquo;</TD></TR><TR><TD CLASS="quote">I am certainly no expert, but I think the change to loop charging could account for the difference.

I have a buddy who says he can port one of these engines, its very mild, but he says they make a ton more power that way, and you don't have to increase compression either. </TD></TR></TABLE>
Well, welcome to the club.
As a bonified non-expert myself. I think we share the same credentials.
I probably pull a little rank on you by having a badge of distinguished dyed in the wool "old fart".
That being said and done. I have never wanted to or over power my boat however, when it's time to refresh my engine, (that is if it will ever happen) I have room to play without making my boat unsafe.



You can never have too much money
A girl can never be too pretty
and as you always say you never, ever have to much horsepower

Regards,

[Lockjaw]

The problem with really pretty women is you can't leave them alone or some guy will hit on them. PLus if they know they look good, then you are sunk.

I plan on working with mine as much as I can. I would love to raise the compression, but don't want to have to run super unleaded. Maybe Tony B will have EFI at some point.

I turn 41 this year, so I am certainly no spring chicken either.

[dhagemeier]

good point by the person on problems created by modifying t'stats. Also, you need to consider the number one problem of 2 st outboard failures; vaporlock and fuel starvation due to the boats fuel system not being correct. after repairing or installing a different engine, have a OMC or competent mechanic do a vaporlock test according to OMC standards 9found in the fuel section of most evin/johnson factory service manuals. Any questions call me at 703-517-2626. Thanks, David