Lightening flywheel on the XR650R in progress.

57 replies to this topic
  • Thumpage

Posted March 03, 2007 - 02:31 PM


The flywheel did in fact need to be rebalanced. I was told by the guys at Crankworks that the flywheel was 8 grams out. These are the guys that did the rebalancing:
Kevin is who I had contact with. When they sent the flywheel back to me it was packaged extremely well. They wrapped the flywheel in plastic and then spray foamed it within the box. it was completely incased in the foam within the box. Excellent!
You will notice that they drilled two additional holes that match and line up with the original two and also machined out a section of the same area to acheive the final result.
Here is the view of the rebalanced area. For reference: If the ignition pickup is positioned at 12 o'clock, the balanced area of my stock and rebalanced flywheel is at 7 o'clock. So this is it,

Posted Image

  • BWB63

Posted March 03, 2007 - 07:52 PM


Thumpage great write up!!!!!!! Real cool you took the extra step to make sure it was ballanced. I never bought into that just because you turn it all the same it will still be balanced. I used a vise grip type pliers that have the big arms and take the ends off. I put hardend bolts in the holes that are left in the end. I might have had to drill out the holes a little. The bolts fit into the fly wheel and you lock the vise grip.

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  • Thumpage

Posted March 03, 2007 - 11:37 PM


Thanks alot for the compliment on my writeup. I surely tried to do my homework before considering it. Thanks also for the homemade flywheel holder tip. Let me be clearer though on how you are saying to use it. Are you saying to fit the bolts through the rear holes of the flywheel or maybe having the bolts clamp on the flattened areas of the center 'hub' of the flywheel?

Regarding the rebalancing. In some way it kind of makes sense that the flywheel should most likely keep a certain balance if all that is being done is turning it on a lathe. Basicly the same material all around is being removed. But I guess it doesn't always translate out to be the case. [Read further below for my theory on my particular flywheel] This could be a good reason to have any flywheel checked for balance.
The stock flywheel could still have been a little out of balance from the factory even though it did have a couple balancing holes. But who knows at this point. It was suggested that the factory balancing, if it is done at all, is more of an 'assembly line' standard, if you will. Sometimes good, sometimes not so good.
Kevin at CrankWorks said they would only charge me "if" the flywheel needed rebalancing. Trailtech said the same thing before finding out they could not do the job for an XR650R on their particular machine. Both said they would not charge to check the balance.
Kevin at Crankworks also stated that if the flywheel proved to be within 3-4 grams out, they most likely could not balance it further. Whether it was all about not being able to measure the difference accurately enough within that range or it was just too delicate to try and balance the difference, I can't say. Further inquiry might have to be done on that subject.
I was told by Jeff at Procycle that my stock flywheel was a bit out-of-round before they started the lightening process. It had a very slight flat spot near the pickup. Something like 15 thousands. Obviously not discernable to the eye but certainly noticable to machinists measurements and equipment. Jeff explained that many flywheels are not totally perfect and may vary slightly in some way or other. But he also said they have had some that are very symmetrical.
Maybe the flywheel being out-of-round was part of the reason it needed rebalancing after it was turned on the lathe? Turning the outside diameter down would possibly alter the thickness between the diameter of the flywheel between the flat spot and the rest of the flywheel diameter. The area of the flat spot might remain thicker. One theory anyway...
All this leads to the matter that it is probably prudent to at least have the flywheel checked for balance just to make sure it is not out by too much.

  • hypersthenos

Posted March 04, 2007 - 12:28 AM


Very cool write up. Let us know how it works.

  • Thumpage

Posted March 04, 2007 - 01:23 AM


Thanks. I most certainly will when I get the chance. It may be a couple weeks though. Weekends haven't been too kind lately for me to get out for riding. Just enough time for sticking around and doing some desk chair riding, :applause: .

  • BWB63

Posted March 04, 2007 - 01:46 PM


The Honda tool clamps into the two hole on the front of the flywheel.
There are lots of after market flywheel holders that are exactly like the tool in the picture but, the flat end thingies (technical word) are removed and they weld posts (I used hardend bolts) in the holes by which the thingies were held by. The post will then be at right angles to the arms and long enough to reach into the holes in the flywheel. You holes have been removed so you would need to have your posts extra long to reach into two of the six hole now exposed. The vise grip lays flat on the flywheel with the post going into the holes and then you clamp the vise grip making the post press into the sides of the holes. Mine work on CR80 flywheel and all others with the two holes.....I think that is all of them I know of. I should take a picture of mine and put it on my site.

here is a cheap tool (costs about $19):
Posted Image

Harder to use then the vise grip kind because you have to aply the grip pressure. (It slips off more)

Here is one like mine:
Posted Image

I have little tits at the end of the post (I ground the bolt heads off leaving just a real little lump facing out) to help them from slipping when I am really torqueing on the flywheel.
I know I was redundant but, I hope I got it across clear. I am not that great explaning stuff.

  • hypersthenos

Posted March 04, 2007 - 06:45 PM


I've got the one in your second pic. It's made by Motion Pro & also can be reversed to lock onto gear teeth. Works great & was cheap too. Seems like it was about 25 bucks but that was 15 years ago.

  • Thumpage

Posted March 05, 2007 - 12:55 AM


Great, I wanted to make sure I was assuming correctly. Thanks.
I find nothing wrong with a little redundancy to make sure the point is clear, :applause:
While the original backplate holes are only half circles now, I think it will be safer to still engage those since the backplate steel is thicker than the flywheel body where the 4 new holes are partly exposed. In other words, the flywheel holder bolts or arms will clamp on what's left of the original backplate holes.
I am glad you brought up making the tool. I already have one of the big arm clamps to make one. I will just pick me up another one for cheap during one of Harbor Freight's monthy sales to replace it. There is a Harbor Freight store fairly close to me.
I can probably find something else to use the newly made tool on anyway, so I will now have another different vise grip option. The holder I have seen was completely different than those styles. [Page 177 of the Honda service manual. It is a sort of strap tool that fits up with the recesses of the case where the stator wires boot is located. So, I didn't even know of those flywheel holder types, :eek: . Truthfully, I had tried using a rubber type strap tool to hold the flywheel when I tried removing the flywheel bolt. It held pretty good but I quickly found out there was no way it was going to hold enough to loosen the bolt torqued at 90lbf-ft.
For reference: CRFs, I read, are only something like 47lbf-ft.. So the XR650Rs flywheel bolt is mongo tight, :lol:. I will probably extend upon your idea a little further and drill sizeably bigger holes in the clamp and add bigger bolts,[hardened as well, just as you did] to make sure.
Thanks again.
For additional picture reference for all, I am attaching pics of the flywheels' front views, before and after the lightening process. Also a pic of the flywheel before I took it off. O.K.,.. yes I have a badly leaking countershaft seal I have to replace, :lol:. The stock plastic skid plate is temporary, I usually have my aluminum one mounted. But I digress...

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  • BWB63

Posted March 05, 2007 - 07:02 AM


The reason I left little knobs on the end is because the bolts have to be so long and there is a bunch of flex in the vise grip arms. This makes the post/studs tweek to there sides some when your really get on it to loosen the flywheel bolt. I also used the harden bolts with a smooth shank to the threads, had a nut there and then put it through the holes with a nut on the other side to tighten it up.

  • Estevahn

Posted March 05, 2007 - 10:49 AM


Thanks for linking me to this thread Thumpage.
Do I dare ask what it cost to have the balancing done?

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  • Thumpage

Posted March 06, 2007 - 12:35 AM


Thanks for linking me to this thread Thumpage.
Do I dare ask what it cost to have the balancing done?

Hey, no problem and a "thanks" back to you and 'bcone' for giving me the info for posting pictures to my thread.
Heh, you missed the couple times where I mentioned the cost of the rebalancing, but not a problem. I know the thread has a few long posts now to have to read through. $45 is what it cost for rebalancing from Crankworks. :applause:

  • Estevahn

Posted March 06, 2007 - 11:19 AM


DOH! I missed that.
Knowing first hand what it takes to do balancing, the $20 you'd mentioned in an earlier post seemed awfully cheap. The $45 is money well spent.
The flywheels on my pitbikes were horribly out of balance. After balancing there is a very noticable differance in spin up and spin down as well as vibration. My next project is to do the the cranks. It's quite time consuming and probably not worth it but it'll keep me out of trouble.
Nice thread btw. :applause:

  • Thumpage

Posted March 06, 2007 - 01:26 PM


DOH! I missed that.
Knowing first hand what it takes to do balancing, the $20 you'd mentioned in an earlier post seemed awfully cheap. The $45 is money well spent.

As mentioned early on, Trailtech was the original company that I had planned to do the balancing but it was a no go,[read below].
Their balancing machine uses bike/crank specific spindles to hold the particular flywheel. It sounds less involved to set up the flywheel for balancing and with that said, that might be partly why they can do it cheaper than most.
But if someone has a flywheel from a bike that Trailtech doesn't manufacture one for, they may not have a matching spindle to set it up for balancing and can't do the job. That was the case for the XR650R. They don't make a heavy flywheel for it because it is not a bike that would ever need one, so no spindle for it and no others matched.
Crankworks can conceptually do any flywheel. It may take a little more to set them up, so time is part of the cost. Given that, I agree, the cost seems very fair for the job performed.
It should definitley make a difference in the smoothness factor. Especially when hitting the upper rev range. As you said, "Money well spent". :applause:

  • cleonard

Posted March 06, 2007 - 02:46 PM


While it's a bit late I do have a comment.

I don't know the exact torque numbers, but I found that on my XR600 the nut on the other end of the crank is tightened to the same torque. I just tightened the flywheel bolt against the nut on the other side. No holder needed. There are other techniques as well like putting the bike in 5th gear and using the rear brake to hold it.

I'm not saying forget the "proper" tool, I'm just saying don't let the lack of it stop you from completing your task.

  • Thumpage

Posted March 06, 2007 - 10:59 PM


cleonard, :lol: :lol::applause:
What you are suggesting sounds like you have to remove the right clutch and side cover to do what you are suggesting, :naughty: . That is way over the top for such an otherwise simple procedure. Or, it is the case that the two bikes are completely different in this regard, [and everything else for that matter]. There is no other possible way that I can imagine to access any other crank shaft area or nut. Look at the previous post of the picture of the stator/flywheel cover off of the bike. That is all there is. The flywheel backs right into the engine case with no room behind it.
The whole 5th gear/step on the brake technique I think is doubtful. Using this method for the clutch can work but I don't think it can be used for the torque spec requirement of the XR650R flywheel bolt, :eek:.

  • cleonard

Posted March 07, 2007 - 11:31 AM


I guess that I wasn't thinking about your situation. I believe that the flywheel bolt torque is the same at 90 ft-lbs. I have never taken off the flywheel without doing it for some other reason. Those other reasons always involved taking off both side covers. The first time I did it I followed the manual and I already had the right side cover installed. I did the rear brake method. It does take a good clutch for this to work. I managed to get 90 ft-lbs on the flywheel bolt, but my clutch started slipping at maybe 92 ft-lbs. That was with an almost brand new clutch and extra strong springs. I don't think that the regular springs would have held 90 ft-lbs. I was thinking that the 650R clutch would be beefier than the 600 version.

The proper tools are always better anyway.

  • Thumpage

Posted March 07, 2007 - 09:18 PM


cleonard, I can understand where you are coming from with regards to the clutch.
The XR650R clutch was designed to handle the additional power made by the newer generation motor, so should naturally be somewhat more robust than the 600s. Someone could also try putting a bar in the spokes of the rear wheel while engaging the brake to help lock everything in place. I did think of those things. And on top of that I actually use heavy duty clutch springs.
I guess what I really wanted to imply is, I just would rather keep things as simple as possible while doing it by myself and run less risk of Murphy stopping on by and offering me some help in my garage, :lol:.
But I can agree that it is possible if someone really does want to get it done without 'The Tool'. Thanks for the input. :applause:

  • weskc35k

Posted October 17, 2007 - 12:29 AM


OK so what has transpired?

  • BWB63

Posted October 17, 2007 - 06:02 AM


Rich, did you ever complete this? What was the outcome. Are you going to Glamis this next weekend? I think I am going to have to go deer hunting.

  • Thumpage

Posted November 20, 2007 - 08:38 PM


Hey guys,

I know this is really late in response but I just have not been around these parts for awhile.
As for the flywheel,.. oh boy. First I had a layoff in riding right when I had the flywheel lightened and had not had a chance to even get out. The bike sat, as I had other things off the bike like the bars, chain and other things that I was in the process of replacing at the same time, not related to the flywheel mod.
In any event, finally,.. I have had a problem with the flywheel after some time of thinking the problem could possibly be something else since the bike had been sitting for awhile.
We'll it turns out it is the flywheel. I am in the works of getting to the bottom of this matter and getting things resolved with the shop who did the lightening work.

There was a flub in turning the flywheel that I had noticed right off the bat and addressed this with the shop. Part of the edge of the pickup was machined off during the process. Approximately 1.1mm or .042". I was concerned about the alignment of the flywheel pickup and the stator pickup. I was assured that this would not be a concern, as the front and rear of the pickup area is usually what is most important.
What it is, is that the cutting bit has a 60 degree edge on one side and they machined too close to the pickup on that side, therefore shaving a 60 degree angle off the one side. The other side of the bit is flat and they were able to machine right up to the other edge of the pickup without touching it just like what is normally done.
The bike will start and idle fine but as soon as you crack the throttle it starts cutting out and backfiring. If you open the throttle enough it will just cut out with a big backfire. To absolutely confirm that there was nothing else that could be contributing to this condition, I had the flywheel tested on a friends XR650R and the same thing happened on his bike. So, The cutting of the pickup is what appears to be the suspected problem.
As far as the discussion & dealing with the shop owner, (so far) that did the lightening work, I am not prepared to say much more at the moment. I will wait until things get resolved, or lack there of. We'll see how things go.
I will keep everyone posted.

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