Wrist Pin Fit to Piston

Press or sliding fit?

All Panhead related topics
Post Reply
Mongrel505558
Site sponsor
Site sponsor
Posts: 777
Joined: Thu Mar 26, 2020 5:46 pm
Bikes: Rigid Panhead chopper/bobber, 68 Shovelhead, 2000 Road King Police bike, 2000 Dyna Wide Glide
Location: Rhode Island
Has thanked: 532 times
Been thanked: 294 times

Wrist Pin Fit to Piston

#1

Post by Mongrel505558 »

When I installed new pistons in my motor they were a tight fit. I don't like whacking on anything attached to my connecting rods with a mallet, so I pressed the pins through using a threaded rod with nuts, washers and a socket.This was done with all parts at ambient temperature. Heating the pistons or chilling the pins might have made a difference. I've had tight pins before and I've also had them slide right in. I always assumed that as long as the pin fit to the rod bushing was correct it shouldn't matter. Last night I was killing some time and watched a video of a pan rebuild by Tattro Machine. Tattro took a lot of time honing the piston pin bosses until he got a sliding fit. Holding the piston with the pin axis vertical, and with lubrication, the pins slowly slid down through the pistons. I don't have a Sunnen power hone, and I suspect most people without fully outfitted shops don't either. I've installed pistons on many different bikes more times than I can remember and never had any issues. Is this critical or more a matter of preference?
Thanks

Jim


RooDog
Posts: 3458
Joined: Tue Oct 31, 2017 1:00 pm
Bikes: 1950 Panhead, Resto-Mod
1968 90", 5 Speed Shovelhead,
1984 Custom Built Evo 100" Bagger
Location: Knoxville, Tennessee
Has thanked: 1846 times
Been thanked: 1419 times

Re: Wrist Pin Fit to Piston

#2

Post by RooDog »

That was a good thought from Tatro, Jim. I have had issues with zero clearanced parts from time to time. Slipping together, and at other times needing just a little persuasion. I wouldn't have any qualms using a hand held hone on a piston as long as the rod to pin fit was OK. Just enough working the piston to get the pin through by hand pressure, and nothing more. And of course, lubrication is mandatory.....
Or how about a hair drier/heat gun on the slugs?
....RooDog....
Mongrel505558
Site sponsor
Site sponsor
Posts: 777
Joined: Thu Mar 26, 2020 5:46 pm
Bikes: Rigid Panhead chopper/bobber, 68 Shovelhead, 2000 Road King Police bike, 2000 Dyna Wide Glide
Location: Rhode Island
Has thanked: 532 times
Been thanked: 294 times

Re: Wrist Pin Fit to Piston

#3

Post by Mongrel505558 »

RooDog wrote: Wed Oct 13, 2021 6:08 pm That was a good thought from Tatro, Jim. I have had issues with zero clearanced parts from time to time. Slipping together, and at other times needing just a little persuasion. I wouldn't have any qualms using a hand held hone on a piston as long as the rod to pin fit was OK. Just enough working the piston to get the pin through by hand pressure, and nothing more. And of course, lubrication is mandatory.....
Or how about a hair drier/heat gun on the slugs?
....RooDog....
Can you give me an example of a hand-held hone?
Thanks

Jim
Buddhahoodvatoloco
Site sponsor
Site sponsor
Posts: 1784
Joined: Wed Sep 07, 2016 7:13 pm
Bikes: 1969 FLF
1937 EL
1940 U
Location: san diego
Has thanked: 1219 times
Been thanked: 198 times

Re: Wrist Pin Fit to Piston

#4

Post by Buddhahoodvatoloco »

they look like this..............
Attachments
911-655_A_V1.jpg
911-655_A_V1.jpg (13.22 KiB) Viewed 201 times
RooDog
Posts: 3458
Joined: Tue Oct 31, 2017 1:00 pm
Bikes: 1950 Panhead, Resto-Mod
1968 90", 5 Speed Shovelhead,
1984 Custom Built Evo 100" Bagger
Location: Knoxville, Tennessee
Has thanked: 1846 times
Been thanked: 1419 times

Re: Wrist Pin Fit to Piston

#5

Post by RooDog »

Jim....
email sent....
RUBONE
Moderator
Posts: 7270
Joined: Sat Nov 15, 2008 4:09 am
Bikes: Multiple H-D, Ducati, BMW, Triumph, BSA,...
Has thanked: 261 times
Been thanked: 2121 times
Contact:

Re: Wrist Pin Fit to Piston

#6

Post by RUBONE »

Factory specs were always light press fit with pistons warmed up with a heat gun or propane torch. The pin is intended to rock with the piston and only move on the pin bushing.
nifty
Posts: 114
Joined: Wed Apr 29, 2020 8:24 am
Bikes: 68 FL
Location: Nambour Qld Australia
Has thanked: 43 times
Been thanked: 80 times

Re: Wrist Pin Fit to Piston

#7

Post by nifty »

I second Rubone,
IMO For normal street use the stock set-up, assembled with heat, ensures quieter operation in running engine. Heat guns are great!
Be aware that hone-fitted aluminum pistons and bronze bushings quickly loosen when the microscopic ridges quickly flatten down in use.
Can be mitigated with ultra fine stones and "diamond" laps.
IMO Same applies to bottom end & trans, a fine line-lapped finish in races and polished shafts won't loosen up as much as a Sunnen honed finish and straight out of the box ground shafts & crankpins.
Laborious vs fast.
Nifty
Mongrel505558
Site sponsor
Site sponsor
Posts: 777
Joined: Thu Mar 26, 2020 5:46 pm
Bikes: Rigid Panhead chopper/bobber, 68 Shovelhead, 2000 Road King Police bike, 2000 Dyna Wide Glide
Location: Rhode Island
Has thanked: 532 times
Been thanked: 294 times

Re: Wrist Pin Fit to Piston

#8

Post by Mongrel505558 »

Buddhahoodvatoloco wrote: Wed Oct 13, 2021 7:20 pm they look like this..............
That might be a little extreme for the amount of clearance I'm talking about. I was actually wondering if somebody makes something like an adjustable reamer, but with expanding honing stones instead of blades.
Mongrel505558
Site sponsor
Site sponsor
Posts: 777
Joined: Thu Mar 26, 2020 5:46 pm
Bikes: Rigid Panhead chopper/bobber, 68 Shovelhead, 2000 Road King Police bike, 2000 Dyna Wide Glide
Location: Rhode Island
Has thanked: 532 times
Been thanked: 294 times

Re: Wrist Pin Fit to Piston

#9

Post by Mongrel505558 »

RUBONE wrote: Wed Oct 13, 2021 9:54 pm Factory specs were always light press fit with pistons warmed up with a heat gun or propane torch. The pin is intended to rock with the piston and only move on the pin bushing.
That's good, because that's what I have.
panhead51
Posts: 46
Joined: Tue Sep 25, 2012 7:45 am
Bikes: panhead 51 fl
Location: Burgundy
Been thanked: 8 times
Contact:

Re: Wrist Pin Fit to Piston

#10

Post by panhead51 »

Mongrel505558
Site sponsor
Site sponsor
Posts: 777
Joined: Thu Mar 26, 2020 5:46 pm
Bikes: Rigid Panhead chopper/bobber, 68 Shovelhead, 2000 Road King Police bike, 2000 Dyna Wide Glide
Location: Rhode Island
Has thanked: 532 times
Been thanked: 294 times

Re: Wrist Pin Fit to Piston

#11

Post by Mongrel505558 »

panhead51 wrote: Thu Oct 14, 2021 11:00 am Here is my method.
http://panhead51.eklablog.com/montage-d ... -c30936008
I appreciate the link, but it comes up in French, which I don't know how to read or speak. I tried Google Translate, but nothing happened.
panhead51
Posts: 46
Joined: Tue Sep 25, 2012 7:45 am
Bikes: panhead 51 fl
Location: Burgundy
Been thanked: 8 times
Contact:

Re: Wrist Pin Fit to Piston

#12

Post by panhead51 »

However, I translate it into English at the bottom of the photos.
panhead51
Posts: 46
Joined: Tue Sep 25, 2012 7:45 am
Bikes: panhead 51 fl
Location: Burgundy
Been thanked: 8 times
Contact:

Re: Wrist Pin Fit to Piston

#13

Post by panhead51 »

It's simple.
Once the tool has been inserted into the piston, make 2, three passes and you're done.
Mongrel505558
Site sponsor
Site sponsor
Posts: 777
Joined: Thu Mar 26, 2020 5:46 pm
Bikes: Rigid Panhead chopper/bobber, 68 Shovelhead, 2000 Road King Police bike, 2000 Dyna Wide Glide
Location: Rhode Island
Has thanked: 532 times
Been thanked: 294 times

Re: Wrist Pin Fit to Piston

#14

Post by Mongrel505558 »

panhead51 wrote: Thu Oct 14, 2021 12:54 pm It's simple.
Once the tool has been inserted into the piston, make 2, three passes and you're done.
I've actually done this for a lot of different things. Just haven't put too much thought into this since the consensus seems to be that it's okay for to have a press fit into the piston.
RooDog
Posts: 3458
Joined: Tue Oct 31, 2017 1:00 pm
Bikes: 1950 Panhead, Resto-Mod
1968 90", 5 Speed Shovelhead,
1984 Custom Built Evo 100" Bagger
Location: Knoxville, Tennessee
Has thanked: 1846 times
Been thanked: 1419 times

Re: Wrist Pin Fit to Piston

#15

Post by RooDog »

to all....
We are dealing with ambient room temp, about 70*, at assembly time, a running engine's parts are at quite a bit higher temp, and all the running clearances are quite different than when cold. We all know this. And surely the piston to pin fit loosens up or else there would be no need for the keepers at both ends of the pin, no? Many automotive piston run without keepers. The small end of the rod is heated and the pin presses in and is locked to the rods by a friction & shrink fit. Harleys', on the other hand, are full floating with running clearance at three points and with keepers on both ends. Forget to install, or lose a keeper, and see how that turns out.... Not too good....
Yes there are ways to enlarge the pistons' bore, but are probably not a good idea, reputable manufactures generally know what they are doing if they sell a "pin fitted" piston kit. But not a bad practice to double check clearances and fit of new parts
....RooDog....
Post Reply

Return to “Panhead”