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View Full Version : Chain slack and twins vs IL-4's



Anonymous
Fri Jul 25th, 2003, 12:49 PM
So here's the short summary: On an email list I participate it, there was a discussion recently about how to adjust chain slack. What I wrote was that Honda (this is a superhawk list) based their slack recommendations on the bike being unweighted. If you weight the bike, then line up the centers of the swingarm pivot and sprockets to find the point of most chain tension, adjust to be snug (but not tight) there, and you're done. Otherwise follow the book.

Someone else replied and said he adjusted it with them centered, but with the chain just hitting the exhaust header (we have dual pipes so headers on both sides) intentionally. Naturally this would result in the chain sliding all over the header when not centered, so he puts a hose clamp on there to protect the header and replaces the clamp when it wears out. He said this was how he was taught by "a guy who forgot more about chain tension than I ever knew" (this reply was after I questioned that practice).

His justification was that, as he put it, chains on a V-twin need MORE slack than those of an inline-4. He said that the power pulses were harder on a twin. Now, granted the pulses of a twin will not be as smooth as an inline, and they are not on a 50/50 cycle based on the crank rotation. However, it's not like the engine is putting more power out. It's still producing just as much HP, but the pulses come half as much as an inline. Anyway he seemed to think that this meant that the chain should somehow be looser.

I think he's full of it, personally. Anyone care to comment? What do you think? Should the erratic engine pulses of a twin require (for reasons I just can't figure) a looser chain than an inline, all other things being equal? :?

MR2FAST
Fri Jul 25th, 2003, 01:33 PM
In my humble opinion Ralphy; HELL NO!!! That is one of the most ridiculous things I've ever heard! I can't imagine the theory behind this, why would you want your chain so lose that it hit's or "wears out" anything on the bike except the chain wax?!
That's like saying, I should remove my air filter because I would get more power if I didn't have any restrictions... (Ya, but I would get so much crap in the engine it wouldn't run, then I would have super pushing power)

Just my opinion...

Ytry2
Fri Jul 25th, 2003, 03:11 PM
:lol: :321: :guns: ok... and your counter shaft sprocket does not turn smoothly, it turns like the second hand of a clock.

tick tock tick tock

because of this action giant butt marshmellow eating squids will come and give you a 100 dollar bill if done right

Anonymous
Fri Jul 25th, 2003, 03:15 PM
:lol: :321: :guns: ok... and your counter shaft sprocket does not turn smoothly, it turns like the second hand of a clock.

tick tock tick tock

because of this action giant butt marshmellow eating squids will come and
give you a 100 dollar bill if done right

:spit: :lol: damn dude you're on a roll today... :lol:

yeah I was 99.5% sure it was bullshit, but hey apparently this guy has forgotten more than I've ever known, so I could be wrong. :roll: :idea: :D

FWIW I told the guy it was flat out absurd when I first heard it, and I think he got a little bent out of shape. His reply was, shall we say, a bit less than friendly. Ahh boo f'n hoo. :321:

mikesf4i
Fri Jul 25th, 2003, 09:13 PM
"Power pulses" are why you have a rubber damper in your rear wheel. The highest stress on a chain is when it is too loose and allowed to flap around. Do you remember when we were kids and played "crack the whip"? the highest stress would be when the chain slack reverses direction. Like the stress on a piston or connecting rod at the top or bottom of its stroke. That is why engines do not rev higher than they already do.

Anonymous
Fri Jul 25th, 2003, 09:23 PM
Do you remember when we were kids and played "crack the whip"?

Sounds like the sort of thing Hoopty and Big-J's mom would be into... :twisted: :lol:

Yeah I know what you're saying, and I agree with you. If it's loose, the excess play will result in high stress while it flops around, not to mention the damage that has to result from it slapping the header constantly.

I just had to post this, 1. in case I was wrong and am missing some fundamental concept of physics here, and 2. for entertainment value. :D

BladeRider
Sat Jul 26th, 2003, 09:48 PM
His justification was that, as he put it, chains on a V-twin need MORE slack than those of an inline-4. He said that the power pulses were harder on a twin. Now, granted the pulses of a twin will not be as smooth as an inline, and they are not on a 50/50 cycle based on the crank rotation. However, it's not like the engine is putting more power out. It's still producing just as much HP, but the pulses come half as much as an inline. Anyway he seemed to think that this meant that the chain should somehow be looser.
Even if his theory was correct, which it is to some degree but not how he thinks, why would you run the chain looser? I would think you'd want to do the opposite and have a tighter chain since there's more delay between the power strokes which would allow the chain to slack more before the next hit. Running it tighter would reduce any reverse lateral movement the chain would have after the power hit.

The other problem with his theory is that power stroke runs thought a multidisk clutch system and through a set of tranny gears before it ever gets to the sproket and chain. Enough of the pulse would be obsorbed in the clutch and any gearset back where the chain would never notice it.

Another problem is with the speed of the crankshaft in relation to the sprocket. Say your motor's spinning 6k rpm. Thats 600 revs per second at the crank which goes through gear reduction at the clutch hub and even further reduced by the gearset. By the time it gets to the front sprocket, there's probably a couple of hundred pulses for 1 turn of the sprocket. The space difference between an I4 and a vtwin is probably in the tens of thousanths of an inch. Way beyond any wear spec of a chain!

This "theorizing" reminds me of being at a highschool party when some of the guys would smoke some grass and start geeking out how they thought things worked. Sounds good at the time, but I bet the next day they couldn't remember wtf they were talking about. ;)