Crunching sounds from tensioner?

Raddion

Raddion

New Member
#1
#1
Hello fellow minibikers...

The wife and I have been testing out our slightly-more-powerful Doodlebugs on the trails, and I have noticed that both bikes make not-so-good crunching sounds as speeds over maybe 15mph are reached. If we're torquing them up a hill, everything is fine on harder acceleration, but as the grade levels off and you back off on the throttle a little, it's almost like the chain is slipping around the rear sprocket or hitting the teeth crooked. I try to ride with my head twisted down and backwards to see what is going on, but it's difficult to pinpoint. I don't think it's a motor vibration issue, as I do have heavy reinforcement plates in there, but I suppose it could be. It's not exactly a "minor" crunching, it's pretty alarming when it happens. You're like, "My chain is going to snap and I'm going to have to push this damn thing home!"

I think the chain could be wandering around as it passes over that adustable tensioner pulley thingie (that I have never seen on any other minibike ever) and causing a ruckus as the rear sprocket teeth pull it back in line?

I have seen in many of the pics of modified Doodlebugs on here that a lot of people seem to just take that tensioner off the bike? I like it because the big Tecumsehs barely fit in the available space, so I don't have a lot of leeway in regards to sliding the engines back and forth for chain tensioning, and that stupid pulley helps me dial it in. Does everybody here toss them because they cause problems? If this has already been discussed, please feel free to point me towards the proper thread, and thanks.
 
Boostinjdm

Boostinjdm

New Member
#3
#3
#1 Your chain should not be tight. You should have just a bit of slop in it. Put your finger in the middle of the longest span and lift up. Chain should move maybe a 1/4" or so without applying much pressure.
#2 Roller tensioners work best with a rib in the middle for the rollers to ride on. Also, delrin is better than metal.
 
texasfabguy

texasfabguy

New Member
#5
#5
Chain mite be stretched. If it gets tighter in spots as you roll it then replace the chain. I buy gold chain that is pre-stretched,they last for years if lubed well.
 
C

Camjamsdad

Active Member
#6
#6
Delrin is usually a white slippery hard plastic.

Your pic also looks like the chain could hit the guard? My chains need periodic lubing or they start binding. If the distance from your clutch to your rear sprocket is short enough you don't need the tensioner. Many people make the tensioner spring loaded instead of fixed.
 
Raddion

Raddion

New Member
#7
#7
Thanks for all the replies! Yes, I do have the chain set tight because it definitely gets tighter-then-its-looser as you move the rear wheel around, as iff the rear sprocket is slightly off center. I set the chain tight bc if I set it to "normal" tension, when the rotation gets to the "looser" part, it's REALLY loose. I know about uneven chain stretching, but these are not old stretched out chains, they're brand new outta the box, with a few hours of runtime or so. I guess I was subconciously hoping that setting them tight would make the tight parts stretch out to match the looser segments. I'm going to bring that up in my therapy session this week haha!

Also yes if the chain is loose enough to bounce a little then yes it it able to clang against the chain guard, but thats more of a dinner bell sound than a crunchy sound. I am going to try loosening the chains a little today, and maybe take the chain guards off until I get off my a$$ and modify them upwards and outwards to match the new engines. If that doesn't work and they're still crunching along, I guess I'll try taking a link out of the chains and throwing the roller thing out into the woods and getting one of those aut tensioner setups that was mentioned.

And if THAT doesn't work... I'll be forced to finish painting my Scrambler frame, and throw one of the Tecumseh's on there!! Thanks for the help, I'll take all the advice and give it a shot. It's funny - at work, I fix cars all day long. Timing belts, axles, driveability, transmissions you name it, I do it. But all of my life, I've always had a hard time with little float bowl carburetors and keeping my darn chains on.
 
cheezy1

cheezy1

#11
#11
First work out your rear sprocket issue. The move up the "drivetrain" from there. As far as the tensioner...I have always switched them over to a snowblower small belt pulley. They work great and keep the chain from walking off if its looser. Every bike starts as a project. And like any project..you must go back and work out any bugs with it. There are no quik fixes. These are small and basic machines...but the end result of improper fixes can be catastrophic to the driver and the bike. And I dig you made a "his and hers" version. Nice to see you have someon e to share the hobby with. Makes it funner. Good luck:thumbsup:
 
Raddion

Raddion

New Member
#12
#12
Hey Cheezy where do you get the small snowblower belt pulleys, is there a specific pulley you use, or will just any snowblower pulley work... although I live in New England, I've never actually even owned a snowblower!

Also, do you guys make up your own spring auto tensioners, or is there already a proven design floating around... thanks again to all who have replied.
 
Harleys Papa

Harleys Papa

#13
#13
Raddion I might have one of those pulleys :thumbsup: I'll look tomorrow. Where in CT are you :shrug: If your close enough you can come get it :thumbsup: if not I'll mail it to you for the cost of the postage :doah:
 
Arthur Kill

Arthur Kill

Member
#16
#16
Camjamsdad said:
$10. it's your rear wheel bearings. They'll make a grinding and also the loose tight you're seeing
Click to expand...
Agreed.

I went through the same mystery rear grinding sounds a few months ago -- drove me batty trying to find it. I followed Camjamsdad suggestion and did the rear wheel bearings first and low and behold, it solved the problem!

You can get all kinds of weird problems from bad bearings.

And they were cheap too - everyone here told me to find a "bearing supply house" in my area. I was sure there was no such thing but guess what? There were 2 or 3 of them in my immediate area.

The bearings you need are universally known as "6201-2RS" - which translates to 12x32x10 -- there are two of them in your rear wheel. I think I paid about 2 bucks a piece for them.

Search OldMiniBikes for install instructions -- mine were not difficult at all. But if you encounter any trouble, read this:

http://www.oldminibikes.com/forum/doodlebug-minibikes/42349-good-luck.html
 
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Camjamsdad

Active Member
#17
#17
It's a very common bearing. We have stacks of them at work. My new style was grinding. The chain would tighten and then loosen. Bought 10 bearings shipped on ebay for $16. Bought more from OldMiniBikes warehouse. Stole some from work. Whenever I replace the rear tire I replace the bearings.
 
Raddion

Raddion

New Member
#18
#18
A Crunching Update

Update... I made up 2 auto tensioners for the DB30's and we took them out for a test yesterday. It's driving me crazy, it's still doing it. At speeds over maybe 10mph during light to moderate acceleration, out of nowhere comes a sound that closely resembles a large monster with hardened steel teeth munching on a Sherman tank. So pronounced, it feels like the minibike chain is following a Pacman route around the sprockets. Interesting though, I found that on both bikes, you can accelerate through it - when you get past the window where this violent sounding condition is occuring, it magically fades away and you're free to nail the throttle as wide open as you please...
This condition is virtually identical in both bikes: low speed / hi torque no problem. Low torque / high speed also no problem. But in between the two - YIKES!! The tensioners appear to be working perfectly, and I even tried adding a second spring to see if that was the issue. Nope.
While I had them apart for the tensioner modification, I blocked the bikes up and gave the rear wheels a good checking over but they freewheel fine and there's no lumpines or looseness. I mean, these bikes are not exactly high mileage, and they have been stored inside since their cheap OEM motors crapped out soon after purchased new. I get that it still could be the wheel bearings, but BOTH almost-new bikes the same situation?

If my engine-to-rear sprocket alignment was off dramatically (on both bikes), I would think Ithat there would be issues thoughout all speed/torque ranges, but there isn't - once the crunching and binding stops these things are going at least 40 mph with smooth sailing until you slow down to below "the window" and then try to reaccelerate. I was almost convinced yesterday that it is a clutch chatter problem, and I suppose it could be, but damn the epicenter of that mechanical maelstrom sure seems to feel like it's from the vicinity of the back wheel. I've got some brand new wheel bearings downstairs that I ordered for another project, I guess it's time to whip off a Doodlebug wheel and see if that's the issue here. Can you post short movies on this forum? If the wheel bearings don't fix it maybe I'll have my wife catch this hellish crunching on video and post it here for dissection... thanks again for all the ideas!
 
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Camjamsdad

Active Member
#19
#19
I rolled the new style doodle out of sears in December a couple years ago, brand new. In January I experienced the grinding. Cheap chinese bearings. On the other hand the well worn old style that I bought to rebuild had original bearings.

You'll prolly wanna ask if there's an easy way to remove the bearings before you try.
 
RobertC

RobertC

#20
#20
Arthur Kill said:
Agreed.

I went through the same mystery rear grinding sounds a few months ago -- drove me batty trying to find it. I followed Camjamsdad suggestion and did the rear wheel bearings first and low and behold, it solved the problem!

You can get all kinds of weird problems from bad bearings.
Click to expand...
X 2 :laugh:

same thing here last year...voracious crunching, loose tight of chain, chain flyin' off !!, all sorts of fun....replaced the bearings, and wa-la ... no more crunch.

I can see both bike's bearings going bad at about the same time also, if y'all have been following each other around, both bikes have taken similar stress.

I don't know the technical where-withal to explain it, perhaps one of the engineering type folks here can help explain, but I can also see how with bad bearings, the wheel could possibly feel ok for a bit, then when speeded up, gets the dang shakes...and then at higher speed would smooth out... (i guess similar to the way a speed wobble could with an unbalanced tire...at some points they smooth out...others feels like the front end is going to shake off ! :eek: ! )

Anyway, my two cent's worth...good luck and keep us posted as to the resolution.
 
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