Will any "F" series piston, rod and crank fit any "F" block? - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information
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post #1 of 7 Old 06-03-2019, 09:17 PM Thread Starter
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Will any "F" series piston, rod and crank fit any "F" block?

I've got a late model "F" engined delux Lawnboy with 3-speed transmission and electric start that I bought as salvage. The con-rod is busted and the crank is scored. Suprisingly the cylinder bore is not scored. I would like to take the piston/rod/cranshaft out of another scrap "F" engine mower, a few years older, but still late enough to be compliance. I thought I read somewhere that ALL "F" engine internals were the same? Is that correct?
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post #2 of 7 Old 06-03-2019, 10:06 PM
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Talking Re: Will any "F" series piston, rod and crank fit any "F" block?

To the best of my knowledge I have never seen more than one piston and rings for an F series. If you have the model numbers of the mowers it would be an easy cross check. Bill

1968 Lawnboy Model 3054******1973 Lawnboy Model 8231******1974 Lawnboy Model 5023
1975 Lawnboy Model 5024******1975 Lawnboy Model 5273******1976 Lawnboy Model 5274
1976 Lawnboy Model 8234EX****1977 Lawnboy Model 5024******1978 Lawnboy Model 5269G
1979 Lawnboy Model 7268******1980 Lawnboy Model 5247******1982 Lawnboy Model 5247
1982 Lawnboy Model 5247*******1972 Lawnboy Model 1015******1972 Lawnboy Model 1015
1987 Lawnboy Model 1400CL****1995 Lawnboy Model 61638

Where there's a will, there's Mr. Bill!***They don't call me MacGyver for nothing!***I have LBAD and DCAD!
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post #3 of 7 Old 06-04-2019, 12:08 AM
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Re: Will any "F" series piston, rod and crank fit any "F" block?

The only exception I can think of is some had a thrust bearing on the lower end of the crankshaft. I don't recall if the crankshaft was different or just the crankcase machined for extra clearance for thrust bearing.
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post #4 of 7 Old 06-04-2019, 11:51 PM
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Re: Will any "F" series piston, rod and crank fit any "F" block?

I did a little checking today and crankshafts, pistons and rods should interchange. Self propelled crankshafts used on models that have drive shaft out the back will not interchange due to larger diameter lower shaft and helix gear on shaft will only interchange with same style engine. 1996 and 1997 F engines used thrust washer and thrust bearing on bottom of crankshaft. These use the same replacement crankshaft as very first F100 so all crankshafts of this style should interchange. Thrust bearing and thrust washer can only be used with crankcases that originally came with them.
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post #5 of 7 Old 06-09-2019, 06:33 PM
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Re: Will any "F" series piston, rod and crank fit any "F" block?

Thank you for the info Old Lawnboy. I have 3 F engines with aluminum Walbro carbs and a 4 square JC Penney with a plastic carb. Can I use a Walbro instead of the plastic carb? TIA
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post #6 of 7 Old 06-09-2019, 10:44 PM
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Re: Will any "F" series piston, rod and crank fit any "F" block?

Quote:
Originally Posted by andyma View Post
Thank you for the info Old Lawnboy. I have 3 F engines with aluminum Walbro carbs and a 4 square JC Penney with a plastic carb. Can I use a Walbro instead of the plastic carb? TIA
Yes you can. You need the type with the primer and choke. Next, you need to trim about a quarter inch off the air-vane in order for it to fit in the baffles of the pre-compliance engines. You also can remove the choke plate if you just want a simple two speed carburetor.

Mowers:
1970 - 5239 (D-408)
1973 - 3058 (D-433) (Rebuilt)
1974 - 8251 (D-480)
1975 - 5273 (D-601) (Rebuilt)
1982 - 7071 (F-101) (Custom)
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post #7 of 7 Old 06-10-2019, 10:11 PM
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Re: Will any "F" series piston, rod and crank fit any "F" block?

Thanks for the prompt reply, Old LB. I was hoping to be lazy and use the Walbro, that needs the needle and seat kit I bought last fall for my nicest Gold Series pusher. But not if I have to modify anything just to test run it before junking the steel deck. I'm mostly interested in the coil's condition. I managed to get 3 totally gunked up Walbros fixed good enough to test the coils. Looks like there's a plastic carb in my future
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