1972 Shovelhead motor question
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Novice
Joined: Mar 2024
Posts: 19
Likes: 3
From: Kentucky, USA
1972 Shovelhead motor question
Hello all ive read on HDF before but made a account today to ask and get opinions on a 1972 Shovelhead motor.
The bike was my papaws and he passed away a few years ago and left it to me. Im currently redoing the whole bike as a learning experience and it was something he wanted tp do before he got sick.
I rode the bike some and had to issues before deciding to tear it down, probably the last time he had it apart in anyqay was the late 80s.
when i pulled the cylinders off i noticed that the wrist pin keeper fell out onto the table and discovered the cylinder had a scar down it. I am not sure how deep it is but it is noticable. I was told that it could be bored but they were worried about it being too much and that it may not last. I cannot remember the bore size they said right off, i got the information second hand.
I thought buying the cylinder and piston set, but as it was my papaws and i would love to keep it the same as it is all original parts minus a s&s carbuetor. My question would it be possible to run the original cylinder jugs without any issue with some honing done to clean it up? As said earlier i rode the bike around as it was for a few months till winter came and decided to work on it. Any opinions or ideas are welcome and would appreciate any help on this so i can my papaws bike back on the road in his memory!
The bike was my papaws and he passed away a few years ago and left it to me. Im currently redoing the whole bike as a learning experience and it was something he wanted tp do before he got sick.
I rode the bike some and had to issues before deciding to tear it down, probably the last time he had it apart in anyqay was the late 80s.
when i pulled the cylinders off i noticed that the wrist pin keeper fell out onto the table and discovered the cylinder had a scar down it. I am not sure how deep it is but it is noticable. I was told that it could be bored but they were worried about it being too much and that it may not last. I cannot remember the bore size they said right off, i got the information second hand.
I thought buying the cylinder and piston set, but as it was my papaws and i would love to keep it the same as it is all original parts minus a s&s carbuetor. My question would it be possible to run the original cylinder jugs without any issue with some honing done to clean it up? As said earlier i rode the bike around as it was for a few months till winter came and decided to work on it. Any opinions or ideas are welcome and would appreciate any help on this so i can my papaws bike back on the road in his memory!
Seasoned HDF Member
Joined: Oct 2015
Posts: 13,488
Likes: 34,570
From: Pine Flat Dam/South Bay Area, CA
You will need to measure the cylinder bore before you can make any decisions on where to go forward. You need to find a reputable shop to do the machine work necessary to freshen up the engine. Have fun with it and it will be a great reminder of your paw.
Thread Starter
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Novice
Joined: Mar 2024
Posts: 19
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From: Kentucky, USA
Seasoned HDF Member
Joined: Oct 2015
Posts: 13,488
Likes: 34,570
From: Pine Flat Dam/South Bay Area, CA
If it has the factory cylinders, they can be bored out .070 oversized. If it's the rear cylinder that lost the wrist pin clip, be sure to check the rod bearings. If one side of the bearings on the female rod go bad, the rod tries to push the wrist pin out of the piston and that's why the clip comes out of the groove in the piston a lot of times. This only happens to the rear cylinder as the front rod has one set of bearings and doesn't put side thrust on the wrist pin.
Seasoned HDF Member
Joined: Aug 2008
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look at the pistons as they will tell you the size.
you cannot run that cylinder without serious issues. say if the groove is .003 deep, it would require at least a .006 over bore which would require at least a .010 if stock bore and if not, then the next over size that will clean it up. then you have cylinder taper which should not exceed .006, the fsm calls for less. excess taper will lead to early ring failure.
even in strict antique codes, having a replacement part does not void the value as long as it meets the original specifications.
if you insist, you can have the cylinder relined but $$$$$$$. then is it really original?????, not according to your standards.
i disagree with the bad bearing theory, most keeper failure is re-using them or improper install.
true, most hd shops will not touch old iron but there are plenty of machines shops that will, google is your friend.
you cannot run that cylinder without serious issues. say if the groove is .003 deep, it would require at least a .006 over bore which would require at least a .010 if stock bore and if not, then the next over size that will clean it up. then you have cylinder taper which should not exceed .006, the fsm calls for less. excess taper will lead to early ring failure.
even in strict antique codes, having a replacement part does not void the value as long as it meets the original specifications.
if you insist, you can have the cylinder relined but $$$$$$$. then is it really original?????, not according to your standards.
i disagree with the bad bearing theory, most keeper failure is re-using them or improper install.
true, most hd shops will not touch old iron but there are plenty of machines shops that will, google is your friend.
Thread Starter
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Novice
Joined: Mar 2024
Posts: 19
Likes: 3
From: Kentucky, USA
I appreciate both your answers. I was told they could not be fixed by one person but I believe I will try to find a 2nd opinion around the area. Think I may have lucked out and found somewhere to check with. If not I will just buy a new set and get to work in it. Thank you all again.
Seasoned HDF Member
Joined: Oct 2015
Posts: 13,488
Likes: 34,570
From: Pine Flat Dam/South Bay Area, CA
I appreciate both your answers. I was told they could not be fixed by one person but I believe I will try to find a 2nd opinion around the area. Think I may have lucked out and found somewhere to check with. If not I will just buy a new set and get to work in it. Thank you all again.
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Seasoned HDF Member
Joined: Oct 2019
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From: OH
Originally Posted by Ghostrider
If not I will just buy a new set and get to work in it.
Last edited by djl; Mar 26, 2024 at 09:14 AM.
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Thread Starter
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Novice
Joined: Mar 2024
Posts: 19
Likes: 3
From: Kentucky, USA
Thanks again everyone. I may have more questions as i get to going on it, ill post them on this thread along with pictures of progress. Luckily i have the original service manual with it so ill have it to lean on.
Road Master
Joined: Mar 2012
Posts: 1,017
Likes: 981
From: Ohio
If the motor is a '72, and is essentially original, the standard bore size is 3.437". The OEM HD 74" cylinders can be bored to a maximum of +0.070" oversize, a nominal 3.508" bore. So just a seat of the pants inspection, if the scar is anywhere near 0.060" (1/16") then the cylinder is most likely unserviceable. If it were mine, I'd also want to the keep the original cylinders if at all possible. So seek out a competent motorcycle machine shop, and have them inspect the cylinders. If the one cylinder is beyond boring to correct the damage, they can be sleeved. That's always a solid option to repair the cylinder.
It's also possible to find a good used OEM cylinder, but since they're getting older finding a good used cylinder is getting hard to come by.
It's also possible to find a good used OEM cylinder, but since they're getting older finding a good used cylinder is getting hard to come by.