Topic: FD rod knock – Antique Outboard Motor Club,Inc

This topic has 24 replies, 9 voices, and was last updated 4 years, 7 months ago by stanley.

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September 23, 2019 at 4:23 pm #183940
stanley
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US Member - 2 Years
I have an FD 11 with equal slight play and knock when checked through plug hole with screw driver.What is the most likely source of the play?This was a gift motor and is pretty rough looking.However it has strong even compression and new coils and points,so I’m trying to decide if it’s worth tearing it clear down or just taking parts and moving on.
September 23, 2019 at 5:07 pm #183943
Randy in Tampa
Participant
They needed lots of oil because they were bushing motors, usually the bushings wore out from lack of oil unfortunately they usually need to be run on like 16 to 1 🤔

Rotary valve Johnson’s Rule!
September 23, 2019 at 6:00 pm #183951
frankr
Participant
US Member
Actually, the rods’ big ends are roller bearings and don’t wear. But the wrist pin ends are bushing. That’s where you will find the wear.
September 23, 2019 at 7:56 pm #183955
The Boat House
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- This reply was modified 4 years, 7 months ago by The Boat House.
September 23, 2019 at 8:56 pm #183958
chris-p
Participant
Unfortunately I have a pile of powerheads with thrown rods from previous owners that heard from a neighbour down the street that they could be run on 50:1.

As we know, that is not the case.

The FDs were not as bad as the 5.5s and 7.5s. When these were run lean, rods went straight through the block!

As Frank stated, your problem is the small rod end bushing from lack of oil. Guaranteed. You can repair, just depends on what you want to spend on it.

Sometimes unfortunately we have to make them parts motors. Depends on how bad the play is.
September 23, 2019 at 9:01 pm #183961
stanley
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US Member - 2 Years
The FD11 schematic I’m looking at shows needle bearings on the piston end of the rod and roller bearings on the crank end.That’s why I was curious about where the wear would most likely occur.
September 23, 2019 at 9:14 pm #183964
frankr
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US Member
Sorry, I goofed. FD-11 had needle bearings. It’s surprising you have looseness. Seems to call for more investigation.
September 24, 2019 at 5:32 am #183974
billw
Participant
US Member - 2 Years
Where are you checking for play? If it’s at the top or bottom of the stroke, some feeling of play is normal. Move the crank so each piston is about half way up the cylinder and check. In that position, there should be little to zero play.

Long live American manufacturing!
- This reply was modified 4 years, 7 months ago by billw.
September 24, 2019 at 6:25 am #183977
stanley
Participant
US Member - 2 Years
I’m feeling a bit after TDC on down stroke.I’ll check again,like you said today.
September 24, 2019 at 7:43 am #183978
olcah
Participant
US Member
Not familiar with FD but I had the same symptoms on an RD18. I found the piston rings had about 0.005 inch clearance in their grooves and that was the click I heard and felt. That clearance is well within factory spec. So before opening the crankcase I would remove the exhaust cooling plates to check and see if the rings are just moving in their grooves. Well worth a check. You can check the inner plate for erosion too.
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