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May 8th, 2022
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Joined: Apr 2005
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Hello all I know this is a "chopper" question but...
I have a 1970 650 front subframe with a bolt on British Cycle Supply hardtail (these are streched 4") I am trying to get everything to line up but I am having some problems. When I got the bike I had to replace the rear tire and spokes on the conical hub and had to replace the bolt on hardtail cause it was bent too. I got the wheel trued up right at my local shop and picked up the new hardtail from BCS.
Here is my problem, when I run a center line down the backbone and over the tire my wheel is off center a 1/4" to the right. However the chain is perfectly lined up with the drive sprocket (checked with straight edge and fancy smancy laser guide). I thought that maybe the wheel was trued with an off-set to the right but if it is trued back to the left any I will have clearance problems with the chain rubbing the tire (the chain is a 530 and the tire is a 16" Avon SM on a 16" HD drop center rim). When I attempt to mount the fender the off set is noticable. What do I do? Should there be a slight off-set to accomidate the chain or am I missing something simple?
Matt

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The offset to the right is common & you're probably O.K. The center line of the 16" rear tire on mine is offset by approx. 3/8". A 1/4" offset isn't bad & I've seen some as much as 3/4" (personally wouldn't want to go more than 3/4" tho')

You're absolutely right about the MINIMAL chain clearance back there. On mine, the clearance between drive chain & lower frame rail is extremely close & I constantly keep an eye on proper chain adjustment.

As long as the measurement from center of backbone to end of each axle perch is equal & considering that your sprockets are lined up for allowing the chain to run true, the noticeable offset of the rear fender is normal & I wouldn't worry about it. HTH...


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Matt,

You may be as close to center-line as your are going to be assuming the straight-edge & laser were dead on. Sounds like your wheel offset is good, as well. You don't want to run your chain too close to the tire as you will have some side to side movement in the chain when decelarating, etc. and obvious tire slapping negates alot of cool on a bike. You may have already done this forty times by now, but I would have to recheck the sprocket alignment. Its difficult, depending on the stage of your engine build, to get a straight edge on the front sprocket but I, personally, trust it more than the laser as it leaves something for interpretation. With a straight edge, either it is or it isn't. Any you can squeek out of this area will help.

This is just one of the problems associated with running a wider tire with a power-plant with limited final drive off-set...you run out of real estate to work with. A Triumph engine does not look right off-set in a frame (undesirable real estate). The sprocket center-line (3.125" from frame centerline) is your starting reference, so building left to right, mathematically, there is only so much you can do with the variables that you have and apparently, yours does not add up to be a centered tire. Some run a 520 chain and machine the sprocket to offset the chain away from the tire, allowing the rim to be shifted back toward the sprockets (.100") but having to machine sprockets (harder than the hubs of he11) is a PITA every time you change your chain and sprockets (expensive real estate). Therefore, after you have milked everything you can to move the wheel left (without compromising anything), then you have to rely on "optical illusions" through fender selection and placement, etc. If the fender is offset in the frame .125" and the wheel offset .125" in the fender, its less noticable than having the fender perfectly centered with the wheel and the fender & wheel offset .250 in the frame.

I can appreciate you working hard to keep everything centered as it is the right thing to do, however, many production bikes and most customs have rear wheels that are not perfectly centered, either. Its just not as noticable on them as they are not as bare or clean as what your are building. Now that you have run into this situation, you will pay more attention to how the wheel is offset in other customs and figure out how they disguise it or "offset the inability to offset enough".

Z

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Thanks guys,
off-set it is. I can live with a 1/4". The fender will be fine as well, I just may raise it a bit higher to move it a bit to the center to help with the look. Hell, when I am riding I won't care what it looks like under my ***!
Thanks again,
Matt

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savageskeeter,

I ran into this the first time years ago with a 1968 Triumph 650 chopper that I "put together".
I simply mounted the fender over the wheel so that it was affset with the wheel.I was running the Avon SM MK ll 5.00x16 as well and a British front 4" fender as my rear fender, plain not ribbed.

beerchug


Jon W.


1957 6T Thunderbird 650
1968 T100R Daytona 500
1971 TR6R Tiger 650
1970 BSA A65F 650
1955 Tiger 100 - Project
1971 BSA A65 650 - Project
1972 Norton Commando 750 "Combat"


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One note IMPO when building choppers with bolt on hard tails. When you are sure you have everything lined up and ready to button down WELD the bolt on to the mainframe. I have pulled many of these things apart and found Grade 7 harware broken and bent like a pretzel. The areas of connection on these components is a pivot point and endures a lot of stress.


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I second the welding notion. I could never trust a "bolt" on hard tail. I always weld mine in place too.

ALSO. You said your BCS hardtail was bent. I had a friend who also receive a bent/mis-manufactured hard tail. We were able to correct it only by replacing the lower cross-brace with a longer piece of tube. It was obviously too short to begin with and was drawing the sides in so far that we couldn't even get the wheel between the axle plates. I was just wondering if anyone else has experienced this and if it is much more common than I thought??

Anyone?

Ryan


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The hardtail frames I've used have all been vintage ones from the '70's & never had any problems with them.

I honestly don't mean to slam BCS, but have heard others mention having to alter some of the newer bolt-on sections received from them, so if your's was BCS, then you're not alone.


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Thank you caffeine!!!

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Hey George.... been doing any refrigeriding lately?

Took the Bonnie out a couple days ago. Squeezed the motor so hard I burned my kneecaps on the head.

I think I got Icecicles in my eyes!

Ryan


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HA! I am such a wuss! My cut off temp seems to be about 55 degress... well, to be honest, more like 60. LOL... But I've heard rumors that 60 degrees is ON ITS WAY! And when it does, out riding I will be. I still have to get the alternator/charging problem sorted out. I'm not sure where the problem is, but battery not being charged. Have a new alternator in a box just waiting to be put in. I'm so lazy. I DID get the handling issues worked out on my hardtail stretched chopper. BTW, although there are numerous posts here on this site about "easing" your ride on a hardtail by deflating tires, there are some very negative consequences to that route in regards to handling. Tires are meant to be run at a recommended pressure for a reason. smile

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Tomorrow. Wednesday! 62 and sunny! Even you can enjoy that one!!

R


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