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Garden Tractors and Mowers Vintage lawn and garden tractors, mowers, snow blowers, snowmobiles and other old machinery that is driven by small air cooled engines.

Garden Tractors and Mowers

Onan Engine Swap


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  #1  
Old 06-03-2019, 07:55:10 PM
TerraNova TerraNova is offline
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Default Onan Engine Swap

Hello Everyone,

Newbie here.

My wife and me are the proud owners of a 76 Massey 1655. Almost certainly the only example of the model in our entire province. Just to get off this island, it's a ten hour drive and then a seven hour ferry trip, so finding another engine isn't easy.

The tractor has a tired Onan 16 twin, a BF-MS / 3221. It did not come with an hour meter but realistically, there are many thousands of hours on this engine. Right now, the engine does run well, a bit of smoke and some oil leaks but, she pulls well.

Recently, I spied an Onan 4.0 RV Gen-set on Kijiji for $ 200 CAD. The owner claims it has just 375 hours on it.

It's a BFA 23/160040 C (hard to be sure all characters are right, the plate is degraded). To me, the heads and block appear identical to our engine. But;

1. The base-pan on the BFA is much larger, 3 Qts vs. 4.5 pts

2. The BFA uses the generator to start the engine, no start motor

Someone told me the BFA used for Gen-sets has a shorter crankshaft than what is found in a BF series. Is that true.

If I have to remove the crankshaft from our tractor engine and swap it with the one on the BFA, what sort of job am I in for.

And, the BF is rated at 16hp @ 3600 rpm, the BFA is 8.5hp @ 1800 rpm. How do I deal with that.

Kind Regards from Newfoundland
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  #2  
Old 06-03-2019, 10:52:14 PM
Georgia SS Georgia SS is offline
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Default Re: Onan engine swap

Hi
I am qualified to give some advise on the onan swap, been there, forget the BFA, If the Bf/MS smokes a bit don't mean it won't run a long time, if you just need something to do replace the piston rings, clean up the valves, if you are looking for an engine, first know the diameter and length of the pto shaft, any 16,18 Or 20 hp engine will fit, even p224 will work but a bit tight, you can transfer your oil pan to any onan you may find. keep all posted, probably get some other comments on this. If you were in south Georgia I could fix you right up with a motor.
Hang In There
Jimmy
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Old 06-04-2019, 10:54:01 AM
TerraNova TerraNova is offline
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Default Re: Onan engine swap

Thanks Jimmy,

My wife and I drove through Georgia a few years ago in late November. Lovely countryside all the way.

So, are you saying the BFA won't work with the crank from the Massey engine ?

The guy selling the gen. had a few other's interested in the machine for use at their cabins and he could not hold it for us. For $ 200 I figured, why not and bought it. At the very least, we'll have a second (well, third gen. to go with the 2,00 watt Honda and the toaster sized 80 watt Honda E-80) generator.

I dragged it home last night and gave it clean-up. Thing looks like it has lived outdoors for some time. All the tins are there, only part missing is the points cover. I filed the points clean. She started immediately when gas was poured in the carb. and ran off a line shoved in a gas-can. No smoke at all and it sounds really strong.

I think for now, we'll store it in our shed and keep fingers crossed the BF continues to stay together. I don't want to tinker with that until I have to. As I said before, it's seriously difficult sourcing Onan engines in these parts.

Warm Regards

Tom
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Old 06-04-2019, 10:09:30 PM
Georgia SS Georgia SS is offline
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Default Re: Onan engine swap

Hi Tom
I have several onans, but only laid my hands on 1 BFA, not familiar with the specs. on the engine, look up a manual on line to get more information about the bore & stroke to be able to determine what can be interchanged, determine the bore & stroke of the BFA, find the diameter & length of the Massey pto shaft to be able to determine the right crankshaft to install into the BFA, the 1800 rpm engine will have all the balls in the governor that you will not want, not a problem, your flywheel, starter, oil pan & charging coil will fit also, that way you could have crankshaft and other parts ready when needed, like such projects, too much good stuff thrown into the trash.
have a good one
Jimmy
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Old 06-10-2019, 09:03:29 AM
TerraNova TerraNova is offline
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Default Re: Onan engine swap

Hi Jimmy,

Sorry, been busy with work.

I found the manual for the BFA. Looks like the cranks are different. They have separate part numbers, however, this may be because the crank for the BFA comes with the woodruff keys while the BF does not.

The BFA has a slightly larger displacement ( 43.3 vs, 40.3 for the BF). But, the stroke is identical. Guess the extra CI`s give the engine more torque at its lower rpm setting than the BF. I can raise the rpm just by pulling the governor lever, so, once I install the old carb and linkage the engine will exceed the 1,800 limit set by the generator control.

One issue remains: the exhaust on our BF consists of two threaded pipes that screw into the heads. The BFA has a header of sorts that attaché to the heads with bolted flanges. Will the BFA`s heads have threaded heads I winder. Can`t tell until I remove the very rusted bolts. Not a chore I`m looking forward to.
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Old 06-13-2019, 10:53:29 AM
Georgia SS Georgia SS is offline
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Default Re: Onan engine swap

Hi tom
i have never found out why onan made the b43 engine, calling it a 16hp, unless they were ready to upgrade to the 18hp and needed to use up all the 16hp parts, what the b43 is, 16hp crank & rods in a 18hp block, b43 & b48 pistons are the same, so you have something good to work with, find you a bf/ms-16 or a bg/48-18 crankshaft with the right pto end for your massey, if you were to find a bg/18 crank you would need the shorter rods also, also will need to remove 5 of the governor balls on the cam gear, i have not been able to find the size of the massey pto. Yes the bfa block will have threads, but i would be looking for bolt on flange pipes, all other parts will swap, your screw in pipes will be mean to remove. Not bad to lathe down a couple of 1" pipe nipples.
Have a good one
jimmy
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Old 06-17-2019, 08:03:56 PM
TerraNova TerraNova is offline
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Default Re: Onan engine swap

Hi Jimmy,

Once again, work interrupted, hard to get all the chores done with so little time.

I'm having trouble finding much in the way of dimensional info on the Onan cranks that were used for different applications. Someone directed me to a site called Tulsaenginewarehouse.com, telling me they had a list of all the cranks used. But, when I tried to find the site, no luck. Seems they vanished about a year ago.

So, unless someone here can certify the crank from our BF will transfer into the BFA without changing the rods, I'd be reluctant to tear-down the BF at the moment.

Why would half the governor balls need to disappear. When I pull the governor lever on the BFA, the rpm's rise well above 1,800. If I place the carb and linkage from the BF on the BFA and disconnect the rev limiting control of the generator, should I not be able to increase rpm with the throttle on the tractor ?

As for the exhaust on the BF; I don't need to remove the threaded pipes (good thing, they have about the same tensional strength as a sea-shell at this point and would shatter if worked with any tool). If all goes to plan, the old BF engine will accept the BFA crank and be used to make the generator functional. I'm more concerned with getting the flanged exhaust pipes free from the BFA block.

Set-up as a gen, the BFA pipes exit the block individually, join together just past the flywheel shroud and turn down to meet the muffler. The 1655 exhaust is 180 deg. oppsite. I have to cut the pipes, and then remove the manifold bolts and reverse the direction the pipes go in. Worst case and the flange bolts break, I can use threaded pipe into the block ?

Thank you and take care.

Tom
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Old 06-18-2019, 02:42:25 PM
Georgia SS Georgia SS is offline
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Default Re: Onan engine swap

Hi tom
yes the crank will exchange, but you don't know how much wear is on the crank journals, there is lots of massey folks out there if they will speak up on pto size, on my sears and lots of other applications the pto is 1 1/8" dia. By about 2 1/2" long, would be good to find a shaft from a bg18, p218, p220 with the correct pto end, a long story on the governor balls, but believe me you only want 5 not 10, if you go with new screw in pipe it will need to be turned down 1/8" on the od. Lots of new gaskets and seals, also lots of luck pulling the timing gears.
Jimmy
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