Machining crankshaft, Yamaha GT1 Yamaha GT80

[@zmotorsports62]

Excellent description of what needed to be done and execution Dale. Love the journey following along in your shop. Mike

[@montana2strokeracer]

Thanks Mike, think I have an email from you too. I am really slow getting to everything right now, just coming out of surgery and a setback, man it is slowing me down, I don't like that. I will get them answered.

[@petermckee1061]

Another lovely job Dale. Chris has asked the question I was going to pose. Crankshaft balance after the "lip/edge" removal. Cheers, Peter.

[@montana2strokeracer]

Thanks Peter, like I commented on his, the metal being removed from around the pin or the pivot area will have no detrimental effect.

[@JohnnieBravo1]

Hey Dale. Awesome stuff here! One thing I'd love to see, maybe even more than cutting a thrust bearing landing on a crank, is fabbing up and machining that crank mandrel! I could watch this stuff all day long.

[@montana2strokeracer]

Hey Johnnie, yes, I understand, and I like providing that type of content, but I know you understand when I say it's nice to just get something done without dragging that camera around. LOL

[@retromechanicalengineer]

Superb work Dale. I can see that I was singing to the choir when I sent you images of my expanding mandrel. It's serendipitous that we are doing the same job at the same time. To address some of the concerns in the comments, when I assessed this work on the BSA cranks, I considered that any effect on balance would be negligible. You are removing material parallel to the crank moment, you are removing quite precise amounts, same on both sides and you are adding the same mass to each side with the washer (within manufacturing tolerance). When you examine the BSA two stroke crank assembly in any detail, you soon realise that balance wasn't very high on the list in the design department! It's a good day if both flywheels are the same diameter. I thought that your fixture was a very clever piece of work. Best wishes, Dean.

[@montana2strokeracer]

Thanks, brother, yep kind of strange that we are doing the same basic operation but going about it a bit different (except for that expanding mandrel). The differences are driven by original design of the crankshafts of course. I think you are spot on about the metal removal so close to the pivot point, I think you could hog out quite a lot in that area and not have any detrimental effect on balance. Gosh, look at the differences in weights of some of the aftermarket rods, pins, and the like, I have had rods on the AT/CT Yamaha's that are 28 grams less in weight and they don't have any negligible effect on the balance of the rotating assembly, at least that I can feel. I suppose at ultra-high rpms it might be a problem, but not what I have noticed with trail riding and an occasional 55 mph burst down the road. I realize the better balance the longer everything will work together and stay together, but in most of these old machines, like you said, balance was not extremely high on the manufactures list of things to worry about. That being said I am ready to see your JIG in action. Thanks for all the spirited discourse on the subject, that's what makes it all so fun.

[@carlwilson1772]

Excellent job Dale. I really liked the fixture for holding the crank. Ingenious.

[@montana2strokeracer]

Thanks Carl, I do have to give most of the credit to my friend Lieuwe in The Netherlands for him getting me going in the right direction.

[@carlwilson1772]

@@montana2strokeracer The great thing about KZbin is this worldwide network of like-minded individuals.

[@montana2strokeracer]

Right on Carl, there is not much that isn't known by somebody, somewhere.

[@geraldsgarage4100]

Love the hose clamps! sometimes you gotta do what you gotta do! Some will say "Thats a stupid setup" I say it's only stupid if it doesn't work! Great stuff!

[@montana2strokeracer]

I know man, sometimes the simple things work the best. But that didn't keep me from thinking this is not the brightest thing I have ever done. LOL

[@douglasmeeker360]

This was a very interesting ride in the shop today. Using an eccentric cam to offset an eccentric cam to create a true circle for turning. Never know what's coming next Dale.

[@montana2strokeracer]

Doug, I scratched my head for days thinking about this, the whole thing seemed sketchy to me, but I like a challenge and my friend from The Netherlands sent me a picture and said this is what you want. So off to the machine shop to see if I could make one. Now you know the rest of the story. LOL

[@sidecarbod1441]

That is a really good jig to hold the crank, nice work! 🙂

[@montana2strokeracer]

I was happy with the results. I do have to give most of the credit to my friend Lieuwe in The Netherlands for him getting me going in the right direction.

[@zxspectum]

Really glad I found your channel, so many tips and tricks, looking forward going through all you videos. So nice to see well shot and explained details around 2 stroke engines.

[@montana2strokeracer]

Thank you for the kind comments, Erik, I hope you can find some good info among these video's or at least some entertainment.

[@donbridgewater2988]

That was an awesome work around for the crank on the lathe. Another awesome job Dale!!!

[@montana2strokeracer]

Thanks Don, it was a bit of a challenge, but I like that keeps the brain working well. Sure, appreciated the help I got from The Netherlands for the jig.

[@hdvette64]

$6.23 in 2024 money. Love this stuff, not too many REAL machinists left in this world.

[@montana2strokeracer]

I know, is it really worth it to them to save such a little amount. Thanks for the kind words my friend.

[@johnfry9010]

Really nice work on that work holding jig and a great outcome !

[@montana2strokeracer]

Thanks John but I have to give the credit to my friend Lieuwe from The Netherlands, I was scratching my head trying to figure out that jig.

[@oldgreybeard2507]

Sketchy? No more amazing machining work. Thanks for posting. Take care

[@montana2strokeracer]

It sure seems sketchy with all those hose clamps. But all jokes aside it was a ridged set up.

[@davidleland8729]

Very impressive repair work Dale! Hopefully I'll never need to do that myself.

[@montana2strokeracer]

Thanks Dave, I sure wouldn't want to do it every day. But it turned out good and I think it's pretty straight forward at this point.

[@peteregger7928]

I was at first thinking what a precise test fixture off-set until I realized you off-set the fixture in the chuck jaws to spin the crank true where you needed it! Nice work!

[@montana2strokeracer]

Thanks Pete, everything is off set on this rig. But it worked like a champ and really wasn't too hard to get centered.

[@jamesws3]

Hey, I got here early! Ready to crank it up and watch!!

[@jamesbanjomanjohnson]

you beat me by 1 minute.

[@jamesws3]

@@jamesbanjomanjohnson LOL, I'm usually quite late and a video behind. Really look forward to Dale's videos. Got lucky for a change. Welcome to the viewing party!

[@markaddy53]

great job dale i woz expecting the steel to be hard there but cut ok glad u sorted it next video please

[@montana2strokeracer]

Me too Mark, I was prepared for that with my carbide insert.

[@ejfredaable]

Thanks Dale!!

[@johnreid2837]

That is really impressive . I wondered how you were going to do that.

[@montana2strokeracer]

Thank you, John, not meant to be, just a lot of wobbling parts, kind of cool though

[@cainbeeping8480]

Good job Dale.

[@chrisgreig5628]

Thanks That was most educational , and Balance ? of the crank changing dramatically .or not .

[@chrisbenn8691]

It won't change. As Dale said, the metal taken out is replaced by the thrust washers.

[@montana2strokeracer]

Thanks Chris, no there won't be any problem with this, or the extra taken out so I can measure. The metal removed is all at the pivot point where the lower pin is, if the same metal was removed at the bottom of the crank halves, you may have a balance issue. Most of the replacement pins and rods that are supplied by the aftermarket are way more out of balance and I have seen no real issues with them either for normal running or riding, super high rpm stuff would more than likely be a problem.

[@jerrypeal653]

That was interesting.

[@KH102695]

Well done!

[@TimWatkins1962]

you are a perfectionist I am restoring a 75 YZ 80 I am not doing the crank a pro is.

[@montana2strokeracer]

Thank you, Tim, this is not a bad job, but having to clean up all that damage makes it one.

[@sidecarbod1441]

30:54...Dale, I call 'witchcraft' on that! 🙂 (Only jesting, you must have been pleased with that 37.94 figure though!)

[@montana2strokeracer]

I know, no one was more surprised than me. When I saw that number on the caliper, I had to check my notes, when they were the same, of course I had to gloat just a little bit. LOL

[@RobertBradshaw-u2f]

That's some hardcore milling Dale!! You couldn't just find a replacement crank?

[@montana2strokeracer]

Thank you, it is a fun project. Yes, I could have found a later model crank, but I would have had to pay about 100.00 for the used crank and still have to rebuild it with a new bearing at least. This was the most economical way to repair the crank. So, in the end doing this way saved the customer 75.00.

[@TiggerTitu-wo1bj]

Trust yourself more Dale. That repair is fine. My question is why you did not do the operation in the mill? If you did not have the right size mill bit, then use a smaller bit and set up on the rotary?? Nice vid as always! You stuff is such a pleasure to watch. Vettepilot

[@montana2strokeracer]

I am happy with the repair; it should be a straightforward build from here. I was going to do it on the milling machine, I even had the correct spot facing mill. I had it in mind early that I wanted to build a JIG and do it on the lathe. Why? who knows......it was more work, scratched my head a lot, made more than one Jig, messed up a lot of material, but in the end, it was fun, it did the job, and it was cooler than watching a wam bam thank you mam straight down cut with the mill. I don't know.

[@TiggerTitu-wo1bj]

Well, as you say, a lot more work, but it might help out people that don't have mills!! Hey, are we going to see a ride on that red AT1MX before the snow flies?? ;~) Robert

[@tintruder224]

The offset expanding mandrel is a great idea and useful for other applications as well. Curious why you didn't just do this on your mill...much less chance of the workpiece shifting. Easy to do with a boring head. Just a thought...not a criticism.

[@montana2strokeracer]

It was just what I wanted to do, I just like the challenge of making tools. I had a spot face mill the correct size and even set it up once. Did it on the lathe anyway. It was fun and made some good content for the channel. I'm retired so I am not in the mind set of having to make money every minute of the day. Guess I'm weird.

[@frankdillon6127]

shop is full, scoot over guys.

[@dralexmclean]

VERY ingenious Dale. How did you mill that slot that the crank sat in. It looks to be the same radius as the crank pin that rests in it. I did wonder why you made the mandrel assembly so long as it would appear that it could have been a couple of inches shorter. VERY slick set up and very nice result, you never fail to amaze me Dale.

[@montana2strokeracer]

Hey Alex, that slot was cut on the mill using a 3/4-inch round nose mill, it did a very good job and was very close to the stub diameter. Yes, the mandrel was about an inch longer than it needed to be with the mag side half mounted on it. I was lazy and didn't want to cut it off, it was within .0015 when cutting the part. Close enough in my opinion. You have to understand that the stub had to be in line with a jaw on the chuck and could not locate between jaws. For fine adjustments. This adjustment was within .0005, so it worked very well.

[@dralexmclean]

@@montana2strokeracer OK, that makes sense, I had assumed you could have pulled the stub could have been pulled back between the pins. Thanks again for taking the time to explain!

[@stephenlesbos6208]

Yamaha will revise a part across a number of years and when the back stock of the old item is worked through they will start supplying the new part for the older model. I have a TZR250 3XV9 which was supplied with a cast crank. The replacement part for this model is now the SP crank which is forged. Yamaha no longer have any standard cranks in their inventory.

[@montana2strokeracer]

Hey Stephen, yeah I think most of the manufactures work that way with their parts. They will just get rid of the old ones when they have designed a new one and when those are gone the new design follows. In this case the part numbers for the complete crank were the same for the old and the new design. But if you ordered the crank halves, they were different numbers. So that leads me to believe the halves are what were modified.

[@cainbeeping8480]

Here

[@yz250a]

Noble, yet unnecessary.

[@sidecarbod1441]

Yamaha updated the crank so that it used thrust washers to they would consider it to be necessary, as to many other people watching this vid.

[@retromechanicalengineer]

Essential for the following reasons: Obsolete crank, spares unavailable. Premature wear of the big end rod faces if left unattended, excessive rod shake causing a noisy bottom end and premature piston wear. Yamaha carried out this modification later on, as another viewer pointed out.

[@sidecarbod1441]

@@retromechanicalengineer Apart from ALL the reasons that you have mentioned it is "unnecessary" ;-)

[@retromechanicalengineer]

@@sidecarbod1441 of course, apart from those.

[@montana2strokeracer]

The mag side crank half was so damaged by the rod that something was going to have to be done. If assembled with the damaged crank half the new rod and bearing would not have lasted long. The other option was to find a good used crank. By the time I did that and replaced the rod, bearing, and thrust washers I would have had more money involved. So, this seemed the most economical repair, and the bonus is it brought it up to the later model crankshaft spec's. Thanks for the comment and for supporting the channel.