Topic: ’56 Lark rebuild: Unusual noise at piston/rod/crank preassembly

This topic has 15 replies, 9 voices, and was last updated 2 hours, 42 minutes ago by Bob Wight.

Viewing 10 posts - 1 through 10 (of 16 total)

1 2 →

Author

Posts
January 3, 2026 at 12:22 pm #302944
Floater
Participant
Happy new year. I just sealed up the crankcase on my project. Before I go further, can a voice of experience assure me that the noise in the video is normal. It’s a studdle knock as each piston reaches it TDC. New rings, piston, bore/hone.

https://youtube.com/shorts/BJWIR6ONbr4

Thanks
January 3, 2026 at 12:37 pm #302947
Buccaneer
Participant
US Member
It doesn’t sound normal to me, but I can’t imagine
what it is either.

Prepare to be boarded!
January 3, 2026 at 2:00 pm #302948
Gary Haight
Participant
US Member
I looks like your crankshaft jumps or skips in the video when you hear the noise. The pistons don’t seem to jump in the video from what I can see. Is it possible to determine if the noise happens on a particular piston stroke when it is all the way up or all the way down? Is the noise coming from the same piston or coming from both pistons alternately? Just trying to help diagnose before you have to pull engine apart again. I don’t know particulars about your engine but could it be a bad connecting rod bearing? I am sure someone may be able to help diagnose the noise.
January 3, 2026 at 2:24 pm #302949
stanley
Participant
US Member
After each piston is started on the down stroke,stop and push on it and see if there is any noise or play.It’s even more effective if you can do this with the head on and using dowel through the plug holes to push on piston.
January 3, 2026 at 5:58 pm #302963
dave-bernard
Participant
US Member
could it be the rings are to tight at the top of the cyl.?
January 3, 2026 at 8:06 pm #302978
Tubs
Participant
It may not be the pistons but the rods or crankshaft touching the case. So many possibilities. Do you feel anything with the hand you have resting on the case?

A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.
January 3, 2026 at 8:30 pm #302979
Floater
Participant
Thanks for the interest from each responder. I attached another clip to demonstrate the slight sound when the piston is on the down stroke and then I push on it. It’s the same with both pistons. I did use assembly lube when installing the bearing retainers which may be slightly dampening the sound.

I can not isolate the original noise as to TDC or BDC or even which or both pistons.

The rings don’t seem tight at the top of the cylinder.

It does feel like the crank could be hitting; but I can’t understand how that could happen.

Listen careful: https://youtube.com/shorts/Q9VXua7IryQ?feature=share

I think what you all are saying is: this is not normal & the cases must be opened again to rectify the problem.
January 3, 2026 at 8:35 pm #302980
Bob Wight
Participant
US Member
It’s sure not normal. In looking at your 2nd video there is some slight play in the rod or wrist pin but the knocking noise at TDC is much louder. I think I’m with Tubs on this one – sounds like a rod cap or the crankshaft is contacting the case during rotation but not sure why that would be. I’m afraid you’ll have to open it up again to look for rod or crank interference in the case.

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1955 Johnson QD-16
1957 Evinrude Fastwin 18
1957 Evinrude 3022
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."
January 3, 2026 at 8:46 pm #302981
Tubs
Participant
Instead of revolving the assembly, try putting both pistons in the center of the cylinders and rock the crank back and forth a bit to see if you still get that sound.

A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.
January 4, 2026 at 9:47 am #302984
labrador-guy
Participant
US MEMBER PAY BY CHECK
Man that sounds like you have the wrong size needle bearings on the crankshaft end. Maybe the rod caps are loose. Gotta fix that knocking!

dale
Author

Posts