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Onan 16 -> 20 hp conversion, anyone?

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I was reading the parts and owners manual for the Onan 16 I have, and it seems the Onan 16 -> 20 HP engines are all essentially the same except for cam height, connecting rod and crank shaft.


Has anyone ever tried to convert a 16 HP Onan to a 20, or done anything to try to increase the HP by swapping parts?


One thing I was curious about, the cam height for the 20 is larger than the 18 and 16, but the part number for all three cam shafts is the same. Are they just ground differently?


I have always read books about stroking engines, ajusting cams, and such, and I don't have the knowledge to do it, but I'd love to hear if any experts here have ever done that kind of stuff on their tractors.

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jack and club

some Onan information for you.


the BF, BG, B43M, B48M, B43G, and B48G ALL used the same camshaft, ( cast # 170-3140 )

these engines range from 40.3 to 47.7 CID. ( BG 49.8 CID )

HP range from 16 to 20 HP.

NOTE the BF block will not accept the longer stroke crank, ( 2 7/8" 3.0" without machine work inside the crankcase )


the P 216, P 218 use the 170-4100 cam.

the p 220 cam is 170-4101.

it is the HOTTEST camshaft of ALL the # listed.


CARB'S are another thing.

a 20 HP will have a larger carb the a 16 HP.



the P 16,18,and 20 all use the same cylinder heads.

they ARE FAR better than any of the others.


thank you. boomer ( the used onan engine parts guy, also NOS and new )


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IS the Bxx numbers an engine model, like P216?


When you say the p220 cam is the HOTTEST, does that mean most powerful, vs. actually producing more heat?


What about the crankshafts in the P216, vs. the P220?


The onan parts manual from this site says the camshaft for all three is 105–0637, is this parts manual defunct?

Edited by FatJackDurham

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