Need opinion: powerhead swap worth the chance????

Hi Guys, I just found a 1973 115hp powerhead (where the 20" lower unit was broken off in an automotive collision). I was looking for a Power Trim unit, (which looks a little bent up but the cylinders look salvagable and the electric motor/hydrolic unit is fine). The engine ran fine 20 years ago when the accident occured, and has been stored since, I was able to turn the engine a little by hand, and it looks clean under the cover. I think I can swap the 1973 1150 power head to my 1968 1250 driveshaft housing, (a short shaft). This proceedure in my aftermarket manuals looks fairly straight forward, and they don't mention any special tools. #1 Is this a "bolt up" job? #2 Do I need any special tools, (I have a fairly complete set of automotive tools)? #3 If the compression is even, (from turning the motor over with the starter), is it worth trying the swap? The blown 1250 is a freshwater motor where the power head has never been off, and the 1973 1150 has not been started in 20 years. Any advice would be appreciated. JR

Re: Need opinion: powerhead swap worth the chance????

Rebuild the carbs and water pump and have at it. ( Were it me, I'd be inclined to use the 125 carbs. ) No special tools required. I wouldn't necessarily worry about a compression test at this time. Oil it up good and hope for the best. If the price is right, it's definately worth a shot. Do a compression test after it has been run for awhile. Numbers now might just be an unnecessary source of concern.

Re: Need opinion: powerhead swap worth the chance????

It would be difficult to exchange the too, because the 125 and 115 use differant exhaust extention plates and gaskets. Goto the BAM Marine site and ck part numbers and you can see the differance in the plates and gaskets

Re: Need opinion: powerhead swap worth the chance????

Laddies just said what I was thinking. It seems that there are some subtle differences between the 1250 and the other inlines, which precluded easy powerhead swaps with other inlines.

Re: Need opinion: powerhead swap worth the chance????

Thanks guys, I looked up the gaskets on Bam and the 1972 1150 had the same drive shaft housing gasket as the 1250 but the 1973 changed. It was hard to get the serial number when I agreed to the terms for the motor and PT yesterday, but I will get it when I go back Thursday to pick up the motor and PT. If it is a 1973 I won't swap, but it looks tempting to try if it is a 1972. I will have to take the power head off the broken housing anyway which will give me a look at the gasket surface. The carb question is interesting. If I put the 1250 carbs on the 1150 I assume their would be more power from the fuel allowed by the larger jets and I think the carbs are a slightly larger models as well. I would imagine timing would possibly have to be adjusted. Would it be a noticable power increase, or just a noticibly larger fuel bill? Thanks JR

Re: Need opinion: powerhead swap worth the chance????

If both engine have tillson carbs they will be KD series carbs with the same venturi size (some 115 used walbro carbs) as long as they are Are tillson the would be no improvement. All larger jets would get you would be a engine that was running to rich, that larger jet crap is just that crap---Bob

Re: Need opinion: powerhead swap worth the chance????

Bigger jets won't necessarily give you more power, the motor has to be able to breathe more air to account for a richer mix. With no other change than carbs it's not likely to help. I suppose you could try the 1150 jets in your rebuilt 1250 carbs and see what happens.

BTW around '72 is where the change was made between the thin exhaust tuner plate, and the thicker tuner plate with redesigned midsection.

'69-'71 all had similar-style thin tuners, some (like the 1350) with a divider in the exhaust outlet to enhance performance.

I have a '72 1400 which is virtually identical insides to my old 1350, but with the newer tuner.

If you pull the lower 'shroud' around the powerhead nuts/bolts on the 1150 you can tell right away if it's like your 1250. The later-style tuner has a noticable joint about halfway down, where it joins the midsection.

Whereas the older version is clearly visible as a thin plate, right under the powerhead.

BTW if it has red-stripe cowlings, likely it'd work, blue-stripes would mean later-style tuner (providing the cowlings are orig of course).

If you were able to locate one of those 5" stub-shafts which came in aftermarket extension kits, you could use your 1250's "shortie" L/U on the longshaft 1150.

HTH.........ed

Re: Need opinion: powerhead swap worth the chance????

Thanks for the info, It is a blue stripe cowling, and likely a 1973 that will not bolt up to the Red stripe 1968. This is great info so I will definately look for the above mentioned characteristics when I get her home. Re: carbs; thanks Ladies, I thought the carb issue favored leaving well enough alone. These Mercs run far to well stock factory 'as is' to tweak them unless one just likes to push the envelope just for the sake of pushing the envelope, (which I typically don't do, since my teen age years: many moons ago). I usually play near sea level or 1000 feet above, and I just like to keep the factory gear in good shape and enjoy it. JR

Re: Need opinion: powerhead swap worth the chance????

My '72 has a blue stripe. You can spot the difference easily from the powerhead base bolt pattern. The older pattern has two extra studs (same as your 1250). You won't find them on the '73 or newer inlines.

ie. 10 Studs vs 8 Studs on the newer motors.

Re: Need opinion: powerhead swap worth the chance????

Hi Guys, Turns out this is a 1978 1150 (serial number 4857047), the boat was a 1973 so the guy thought the motor was the same vintage. I could not see the serial number until tonight (when I took the beast home). Thank God for sawsalls, and thank God the dump let me throw the pieces of the boat away. PT looks very usable. Now I need to go to BAM and look at gaskets to figure out what kind of mid section and lower unit to look for. I may need to start a new post since this is five years newer then I thought when I started asking questions. Does anyone know if a 900 or a 1400 mid section would fit and have the same performance. I would assume that the exhaust extention plates on all these inline six motors of similar vinatge would work. Am I wrong? Thanks for your help. JR

Re: Need opinion: powerhead swap worth the chance????

James:

I happen to have a mid-section from a 1979 115 20" length that I'm not using. Give me an E-Mail to work out the specifics.

skier1@p2kisp.com

Craig

Re: Need opinion: powerhead swap worth the chance????

Thanks Craig. I emailed you at the address you gave, please reply. JR