103ho vs KB piston weight question.
Thread Starter
|
Road Master
Joined: Oct 2013
Posts: 1,002
Likes: 190
From: Penticton BC Canada
103ho vs KB piston weight question.
I'm doing a 110 drop in cylinder build on my 103 ho with KB914c pistons.
The pistons, rings and clips combined weight is almost identical when comparing the KB's to stock.
However... The piston pins included with the KB's are about 40 grams lighter than stock.
The stock pins are about .050" longer than the KB's. Should I cut down the stock pins and use them on the KB's to have
the same weight as stock? Or just install the KB pins and not worry about 80 grams of combined weight difference?
The pistons, rings and clips combined weight is almost identical when comparing the KB's to stock.
However... The piston pins included with the KB's are about 40 grams lighter than stock.
The stock pins are about .050" longer than the KB's. Should I cut down the stock pins and use them on the KB's to have
the same weight as stock? Or just install the KB pins and not worry about 80 grams of combined weight difference?
HDF Community Team
Joined: Jun 2006
Posts: 12,779
Likes: 2,609
From: san antonio
Ran into this problem with a build on one of my bikes a few years back. Rebuilt top end with a piston assembly (piston, pin, rings and locks) lighter than the piston assembly used to balance the crank and had issues with vibration from about 2200 to 2800 rpms up and down the rpm range; the bike was unrideable. Didn't know the piston assemblies were lighter when installed but eventually figured out that must be the issue. Sure enough, pulled the top end down, weighed both assemblies and the new piston assemblies were 17% lighter than the original piston assemblies. Can't recall the exact weights but can pull them out if you are interested.
Discussed the issue with John Dahmer at Darkhorse and while John wouldn't commit to a precise parameter, he supposed that any variance in piston assembly weight of greater than 10%, lighter or heavier would throw the crank balance off and that lighter was worse than heavier. Not knowing what your total piston assembly weighs, it is hard to say whether or not the 40g difference is an issue. I can say that I would stick with KB piston and not cut down the stock pins, particularly if the KB pistons are using different locks.
HD pistons are fairly heavy compared to some aftermarket units. The next build I did with CP pistons, the CP piston assembly was lighter than the OEM but CP offered thicker wall pins which put the CP assembly very close to the OEM piston assembly weight so I did not have to worry about crank balance.
As usual, JMHO.
Discussed the issue with John Dahmer at Darkhorse and while John wouldn't commit to a precise parameter, he supposed that any variance in piston assembly weight of greater than 10%, lighter or heavier would throw the crank balance off and that lighter was worse than heavier. Not knowing what your total piston assembly weighs, it is hard to say whether or not the 40g difference is an issue. I can say that I would stick with KB piston and not cut down the stock pins, particularly if the KB pistons are using different locks.
HD pistons are fairly heavy compared to some aftermarket units. The next build I did with CP pistons, the CP piston assembly was lighter than the OEM but CP offered thicker wall pins which put the CP assembly very close to the OEM piston assembly weight so I did not have to worry about crank balance.
As usual, JMHO.
Thread Starter
|
Road Master
Joined: Oct 2013
Posts: 1,002
Likes: 190
From: Penticton BC Canada
Ran into this problem with a build on one of my bikes a few years back. Rebuilt top end with a piston assembly (piston, pin, rings and locks) lighter than the piston assembly used to balance the crank and had issues with vibration from about 2200 to 2800 rpms up and down the rpm range; the bike was unrideable. Didn't know the piston assemblies were lighter when installed but eventually figured out that must be the issue. Sure enough, pulled the top end down, weighed both assemblies and the new piston assemblies were 17% lighter than the original piston assemblies. Can't recall the exact weights but can pull them out if you are interested.
Discussed the issue with John Dahmer at Darkhorse and while John wouldn't commit to a precise parameter, he supposed that any variance in piston assembly weight of greater than 10%, lighter or heavier would throw the crank balance off and that lighter was worse than heavier. Not knowing what your total piston assembly weighs, it is hard to say whether or not the 40g difference is an issue. I can say that I would stick with KB piston and not cut down the stock pins, particularly if the KB pistons are using different locks.
HD pistons are fairly heavy compared to some aftermarket units. The next build I did with CP pistons, the CP piston assembly was lighter than the OEM but CP offered thicker wall pins which put the CP assembly very close to the OEM piston assembly weight so I did not have to worry about crank balance.
As usual, JMHO.
Discussed the issue with John Dahmer at Darkhorse and while John wouldn't commit to a precise parameter, he supposed that any variance in piston assembly weight of greater than 10%, lighter or heavier would throw the crank balance off and that lighter was worse than heavier. Not knowing what your total piston assembly weighs, it is hard to say whether or not the 40g difference is an issue. I can say that I would stick with KB piston and not cut down the stock pins, particularly if the KB pistons are using different locks.
HD pistons are fairly heavy compared to some aftermarket units. The next build I did with CP pistons, the CP piston assembly was lighter than the OEM but CP offered thicker wall pins which put the CP assembly very close to the OEM piston assembly weight so I did not have to worry about crank balance.
As usual, JMHO.
The KB assemblies are 479 grams and the HD units are about 519, both without rings.
I forgot to mention that this is on a rubber mount Road King.
HDF Community Team
Joined: Jun 2006
Posts: 12,779
Likes: 2,609
From: san antonio
I looked at my notes and the JE piston assemblies that were replaced weighed 656g vs 543g weight of the MTC replacement pistons. Be careful about ignoring ring weights; ring packs can vary from 30g to 40g and 10g could make a difference. The 40g difference is within the 10% margin posited as a limit by John Dahmer, so you are probably OK with the lighter pistons but if KB offers a .230 wall pin which would add about 40g to the piston assembly weight would put you dead nuts on the original rotating/reciprocating weight.
Thread Starter
|
Road Master
Joined: Oct 2013
Posts: 1,002
Likes: 190
From: Penticton BC Canada
I looked at my notes and the JE piston assemblies that were replaced weighed 656g vs 543g weight of the MTC replacement pistons. Be careful about ignoring ring weights; ring packs can vary from 30g to 40g and 10g could make a difference. The 40g difference is within the 10% margin posited as a limit by John Dahmer, so you are probably OK with the lighter pistons but if KB offers a .230 wall pin which would add about 40g to the piston assembly weight would put you dead nuts on the original rotating/reciprocating weight.
I was able to do some more accurate measuring. The KB pin is 88 grams, the stock Harley pin is 128 gr, the KB piston, rings and clips are 2 gr heavier than stock.
I spoke with the nice folks at KB and they are sending me a pair of .200" wall pins that weigh in at 131 gr each. So when all is done, I'll be 5 grams heavy on each rod instead of 40 grams light.
Overall, I'm much happier with this. KB never asked me for anything other than my address, so it looks like I'll be getting them free of charge!!
I've used a couple sets of the KB forged pistons and they are nice looking pieces and I sure can't fault the customer service!
Sponsor
Joined: Dec 2007
Posts: 12,084
Likes: 829
No one can ever make an HD crank assembly free of vibration.
Placing the vibration point in the rpm area where you do not ride most of the time is key.
Thumb of rule is the heavier the piston assembly, the earlier the vibration, and the lighter, the later.
60% balance factor is used here on most cranks.
Scott
Placing the vibration point in the rpm area where you do not ride most of the time is key.
Thumb of rule is the heavier the piston assembly, the earlier the vibration, and the lighter, the later.
60% balance factor is used here on most cranks.
Scott
Thread
Thread Starter
Forum
Replies
Last Post
Roadflyer
Engine Mechanical Topics
3
Sep 17, 2018 02:50 PM
300mmsoftail
Engine Mechanical Topics
2
Apr 23, 2014 07:25 PM
