Can this power head work?

[floridamisser52]

Found a 85 hp power head. The model is 85TL79R. And its a flat back.Would like to know if this is compatable to 1998 90 hp 90 degree crossflow flat back . I hope this is enough info. And thanks for your help

[fitz73222]

No, the 85 is a cross flow design, the '98 is a loop charged design. Not compatable.

[floridamisser52]

No, the 85 is a cross flow design, the '98 is a loop charged design. Not compatable.

It's 1998 spl flat back cross scavenged 90 degree for sure and for certain. Last year they made the crossflow. EPA said no more. Supposedly it has less than a 100 hrs on the rebuild with good spark and 110 psi on all cylinders. I think I have the model # written somewhere . It would be great if it would bolt on and all the stuff would work too.  

[fitz73222]

I checked models for '98 and did find XE90TSLECM which in fact is a crossflow BUT it has the pot belly rear exhaust plate like the other crossflows from the 80's up. All other models I checked for that year are loopers. You say this is a flat back exhaust so I'm not sure what it is. Are your sure its a '98? The original 85's '73-'77 were 92 cu in blocks (flatbacks). They switched everything over to the new style midsection (internal trim and tilt) in '78 but what I don't know is if your '79 was a 92 cu in or 99 cu in like the 90, 115 and 140 when they changed midsections. So if your replacement powerhead is in fact 99 cu in and your '79 is a 92 cu in you may have to also replace the exhaust tuner. Futch, Georgie or deburr may have some insight.  If you go to ishopmarine and go to Evinrude/1998/90 and look up that model number you'll see the potbelly exhaust in the cylinder diagram. I just went back to '77 (flatback) and found that the potbelly exhaust plate on the 85 started in '78 with the midsection change so that probably is when the standardized to the 99 cu in block. So if your current powerhead is a flatback it may be '73-'77 92 cu in. Calling all OMC guys!

[fitz73222]

Bottomline is, I can't find a flatback crossflow produced after '77. All are potbelly exhaust from '78 up regardless of horsepower. I did not completely check 20 years of model search. So if they dropped in an oddball SPL with flatback exhaust, I did not come across it. Sorry I didn't answer your compatability question.

[fitz73222]

SOB I found the oddball! Not sure if this helps you but looks like 1987 they made a 88 hp flatback for one year! J or E 88MSLCUS. WTF! Must have had some NOS parts to create this one..

[Georgie]

I guess my first question is what exactly do you mean by "compatible"?  If you are asking whether an earlier generation crossflow powerhead will bolt to the exhaust housing on a later generation crossflow engine, then the answer is yes.  The ignition system, carbs, throttle plate/lever, and several other fairly minor things (pistons and heads, shifter linkage, some fasteners, etc.) are different, but to my knowledge the bolt pattern for all the OMC V4 crossflows back at LEAST to '79 is the same (my first block was a '79 and I replaced it with an '89 when it blew).   If she's in great shape, with a little bit of research you could make the '79 block fit on your '98 engine and update the peripherals as you see fit.  Might be quite a bit more work than just "bolt and go" though.

That said - the original 85TL79R was a bubble back so I have to assume someone has already changed it a bit.    
http://www.boats.net/parts/search/BRP/JOHNSON/1979/85TL79R/CYLINDER%20AND%20CRANKCASE/parts.html

[fitz73222]

The only issue I had was that he said they were both flatback exhaust plates which is what sent me into a technical tailspin! The '79 wasn't flat and the '98 wasn't flat so what are they?

[futch13]

Up until 96ish, 90's and most 115's had a flat back,  the 88spl until they quit building them had flat backs.  If you notice in the parts breakdowns, there are 2 exhaust covers listed with one being NLA.  That was the flat back.  Roughly in 96 they went to the bubble backs and superceded the flat back number.

The power head should fit the midsection.  THe other change made in the early 90's was the TNT that went from the original TNT to the fastrac TNT

[fitz73222]

On Ishopmarine; its showing bubble backs almost exclusively from '78 until '98 unless their parts diagrams are incorrect.

[futch13]

Probably have updated software, ck this   http://www.marineengine.com/parts/johns ... +Crankcase    Ref # 51  It is showing a bubble back as NLA but if you could find the original part, it would be a flatback.  This is a 1988 but they were all the same.

[GoneFission]

Makin' my hair hurt...   :afro: