Putting together a 91 Johnson GT150 ...need advice.

[z1rider]

.. I really tore this thing up a few years ago, and decided to repair it. Almost no major part was left undamaged. Gearcase had the detent lever pulled out, exhaust housing ( mid ) is cracked, and lower mounts broke in half. Exhaust housing adapter busted up, lower pan, an plastic damaged,.... and a chunk broke out of the crankshaft !! Other than that, not bad . This is a 20" GT, and being a 91 has a two piece driveshaft. I replaced the crank, and the intake manifold, so the powerhead should be good to go. It was a fresh water low hour motor. Now, I have a (standard) 1988 150 25" shaft doner motor for misc parts,lower pan, hardware, intake manifold(that I used). I was going to just buy a new exhaust housing,($150), then worry about the gear case, but today a found a "complete" 89 Evinrude XP 175 (bubble back), with a low water gearcase, and solid land and sea mounts for $300. It's a 20" also. It supposedly has a bad piston. Nice clean good looking motor. Has the same part number exhaust housing (mid) as mine,sooo.... could I use the exhaust housing adapter off the 88 150, and drop my GT150 power head on there, and go boating??? Anybody mixed and matched on these old crossflows? I know, I know, why am I doing this ??? It's a sickness, I guess...and a challenge. Thanks.

[racer]

Yes you can use your adapter plate on the 89 mid to install your powerhead.

[skeeter91]

use the adapter under your "flat-back" motor and swap with the "bubble-back one,and volia! your in bussiness.i got aton of cross flow stuff(stock),lemme know if you need anything,i gotta make some room!whatcha gonna do with the 175?

[z1rider]

Thanks guys. I was hoping that was what I could do. The megaphone is screwed to the adapter, so I will use that also. Maybe the inner upper exhaust housing from the 150. The parts list showed the power head to adapter gasket, (0335503), special to the 91 150, and the 88 150 using p/n 0333658, but I don't see a differance in either power heads or adapters on the 150's.
Skeeter91, I'm going see what is really wrong with the 175 power head, and if it is a piston, or worse, I will probably repair it later.

[EMDSAPMGR]

Your 150GT is a performance model. Nice engine. It has many of the flatback 175 parts on it. Carbs, heads, vented cowl, stiff motor mounts.

[Jason Joe]

Thanks guys. I was hoping that was what I could do. The megaphone is screwed to the adapter, so I will use that also. Maybe the inner upper exhaust housing from the 150. The parts list showed the power head to adapter gasket, (0335503), special to the 91 150, and the 88 150 using p/n 0333658, but I don't see a differance in either power heads or adapters on the 150's.
Skeeter91, I'm going see what is really wrong with the 175 power head, and if it is a piston, or worse, I will probably repair it later.

You want to use the 335503 base gasket it is thicker and less prone to leaking.

[Schramer]

The "175" would be the same as a "235" from the earlier years so maybe look into getting that one running in the future

[z1rider]

The "175" would be the same as a "235" from the earlier years so maybe look into getting that one running in the future

I picked up the 1990 XP 175 today. I will unload it and have it on a stand this weekend. I am diffinitely going to do a compression check, and then go from there. I noticed the heads were Evinrude blue, and the rest of the engine is black, so I checked there part numbers ; 325638, 325639. Looks like it had a tune up! Has a Bob's nose cone, and posi steer solid mounts, also.

[EMDSAPMGR]

The 638/639 are the big bore high compression heads. Were a one year head in 1980 (one model in 1981.) Then not seen again till the 1983-85 2.6 XP/GT models. Definitely the heads to have on any big bore OMC V6!

[Schramer]

Fo sho!!

[z1rider]

Got a chance today to unload and hang the 175 on a stand. Compression was around 140# on th port bank, but #1 was 100, and #3 was 118. # 2 was zero. Pulled the head and found #2 piston smeared. They are .020 over. Thinking about fixing the 175 now, rather than trying to put the 150 powerhead on there.

[EMDSAPMGR]

That #2 cyl may have been running lean. Looks dry compared to the other. The cyl liner looks scuffed from the piston. Possible some abrasion on the side of that piston also. That side of the block may have been running hot. Could be from the thermostat being stuck shut. That would cause an overheat at idle, but the pressure relief valves should flow enough cooling water when on plane. Check to see that the nylon pressure relief valve is not heat-deformed in the stat housing. That could cause an overheat when planning. I'd want to pull the carbs apart and do an autopsy on them. Esp to check the high and mid jets in each throat on the low compression side of the carb. May have a restriction inside the jet, causing it to run lean-then too hot, causing the low compression. Two of the three water diverters appear in the correct location. Any chance that .020 over piston is not a factory one? does not match the others in the block? You can get into thermal clearance issues when mixing pistons from different mfr's in the same block.

[z1rider]

I cleaned the pistons a little to read the part numbers.Number 3 is a different part number. Definitely will be checking the t-stats, and carbs. I found it interesting that the port bank compression was quite a bit higher than starboard side on the good cylinders. Here is a view of the piston through the transfer ports.

[z1rider]

Crossflow corner!

[EMDSAPMGR]

That middle piston has a lot of scuffing going on. It's difficult to see the part number on that one piston. What is it? Would be interesting to know if it's a factory oversize. Would also be good to know what the piston to cyl wall clearance is...was the overbore made to the correct size, or was it too small to account properly for the thermal expansion of the piston once the powerhead heats up. When you look through the exhaust ports on the low compr side, do all the piston rings seem to be intact? Any missing/damaged? You say the pistons are all .020 over-any reason they all don't look identical on the crown?