ty250 crank/case assembly help

[billdapart]

Hello All,

This is my first post on this forum so please bear with me. I have a74 ty250a that I am currently restoring. I am an automotive technician of 6 years and have my basics covered but this is really my first embarkation into the world of motorcycle mechanics.

I have the cases split and had the crank assembly professionally rebuilt and I'm looking to re-assemble and having a hard time with the crank. As far as I can tell the crank will have to be pressed into the bearing, correct? I assume a pipe approximately equal to the inner race of the crank bearing should be used to support the case half and the crank should be pressed in one side first. What would I use to press against the crank assembly and where? Also once I have the crank assembly securely in one half, how would you go about pressing the second half onto the other?

I am sorry if this is a very broad question, I admit this may be a bit over my head but I refuse to give up. I have or am willing to get whatever tools are necessary to do this correctly, and if it means watching over the shoulder of an experienced hand I will do whatever it takes to do so.

Thanks for any help and glad to be a part of such a great forum.

Bill

[alan_nc]

Bill,

Should not be a 'press' fit. Check the O.D. of the crank journal and the I.D. of the bearing. It should be tight but not an interference fit. You may have to do some light tapping with a rubber hammer but not more than that. Lube the seal(s)prior to assembly.

If you have further problems email "Feetupfun" directly with your questions.

Alan

[paul w]

A good trick when building two stroke singles is to put the crank into the freezer the night before you intend to re-build the motor, and leave the crank case halfs, with the bearings in, on some heat source (i put mine on an electric radiator in the garage), if you have everthing laid out ready to go it takes a couple of minutes and "falls" together.

cheers

Paul

Edited October 29, 2010 by paul w

[dadof2]

You probably should NOT press the crank into the bearing as this can put excess force on the races themselves. It is far better to pull the crank through the bearing by having a spacer that matches the inner race and making up a tool that grips the flywheel or drive side nut threads.

This is difficult to describe in words but Yamaha do special tools for this and the procedure is described in their workshop manuals. Essentially the aim is to use methods that mean the bearing seating or crankcase joining processes never rely on putting forces through the ball berings.

Cheers

[billdapart]

Thank you guys for your help! I actually went about measuring this morning and as far as I can tell something is off. The crank which is out of a different set of case halves (thus probably explaining my problem) measures about 30mm give or take a couple thousandths. The bearing I.D.s that I measure are anywhere from 29.93 to 29.85 (seems like one side is much smaller than the other). At this point I am splurging for some new bearings (even though these feel like they are perfectly good) Any suggestions on the best place to purchase crank bearings?

Then I'll probably take the suggestion of freezing the crank assembly and try to heat up the case halves.

Thanks again gang, hopefully this won't hold me back too much more.

[alan_nc]

If your not in a panic to put it back together check Ebay. I have purchased them for under $10.00 a set. If you want them "right now" this place has the best prices I've found:

http://www.boats.net/

Good luck with the project.

Alan

[billdapart]

So after I re-taught myself how to use a set of calipers.. My work has me constantly using metric but whenever I get a measurement tool in my hands I think in standard (thanks to my time working at the machine shop). In short, the bearing i.d. and crank journal difference was within .005" which apparently is ok..

I froze the crank and heated up the case halves on the stove top (didn't make my wife too happy with the smell.. oh and the very small kitchen fire which freaked her out made me laugh... uh.. yeah)

While heating up the case halves the tranny bearings fell out so I figured now or never! I slapped the tranny bearings back in lickity-split. Threw in the crank and tranny components and applied a very thin layer of yamabond to the other case half. Crank fell into the first case half so then I placed those on end and put the other case half on top and with a few taps from my 13oz dead blow it was within a couple mm's of together.. then it wouldn't budge.

I placed my tongue fairly outside my lips and clenched by teeth.. installed the new stainless case bolts and tightened them in crisscross fashion first around the crank, then around the tranny in 3 stages.. She went together really easily and after wiping away the excess silicone and securing the con-rod everything spins really smoothly. I think this thing is gonna run just fine!

Just gotta slap in the new clutch assembly and the electronic ignition and she'll be ready for a carb and exhaust!

It's not the prettiest engine but it should do the job for a little while and it's not too bad for something I took apart more than 10 years ago and let rust in the flooded garage!

Now I can move on to powdercoating the frame and fork chambers.

Thanks everybody for your help, I'll be sure to post up some more follow up here as I get further down the road. (no pun intended)

[richty250e]

Dear Bill,

To make a tool to pull the crank into the case with main bearing installed you can use the following:

Cut the lower 30mm off the bottom of an old rear damper tube then remove the piston rod leaving the remaining section of the damper tube which should fit snugly over the end of the crank and match the size of the main bearing inner race.

Now weld an old wheel spindle nut to the end of a piece of M10 threaded rod.

The nut and M10 rod can be screwed onto the crank (same thread as the flywheel nut) and using a large washer and M10 nut pull the crank through the main bearing using the tube from the shock.

Same principle as the factory tool but using stuff you will probably have lying around.

regards

Rich

[billdapart]

Thanks so much Rich!

I do happen to have that stuff sitting around and will be making myself that tool in the next couple days.

I may just need it in the next couple days as well.

Maybe you can tell me if there is something wrong with my engine as I have it pictured here..

I may be wrong as it has been over 10 years.. but I feel I may have left something out of the internals and will have to crack the case again....

[billdapart]

Wow, this project just went from fun to ARGH!!

So as I pointed out in that last picture the kickstart return spring was missing.. DOH!

I used a puller and pulled the left side of the case off and threw the kick start spring in there, double checking I had everything inside that needed to be inside I welded up a tool for cold-pressing the case halves together. (thanks again Rich!) The tool was made out of an old VW wheel bearing tool and and old VW widow maker (i'll post some pictures tomorrow).

The case went together great and I got the cylinder put on with my fresh spankin' new Wiseco piston and installed the cylinder head. Turned her over and clunk.. clunk.. clunk..

The piston was hitting at top dead center.

I used a mirror through the exhaust port and couldnt see anything wrong so I begrudgingly tore the cylinder head off again (is that copper head gasket re-usable at all or is it now junk?)

Rotated it over with the head off and pow! The piston comes right out the top of the jug and the top ring popped out and sat on top of the cylinder!

So sadly I had this crankshaft rebuilt about 9 years ago by a friend of a friend.. who also supplied the piston.. After checking the piston number come to find out it's for a 76-79 YZ250.. If he got this wrong there's no telling what the shape of the crankshaft is..

So I have a useless shiny 70.50 wiseco piston and a brand spanking new std ty250 piston that i found among the drift.. money is scarce but where would you guys recommend a 1st oversize piston set from?

Time to go get

[tony27]

Seeing as you're in the states give these guys a go, I plan to with my engine rebuild. Works out to be a lot cheaper that buying off ebay as you'll never find a complete kit, bare piston normally around $70, rings $30-35 then you still need a wrist pin & clips

http://wossneronline.com/forged_pistons/index.php?main_page=product_info&cPath=50_52_71_111&products_id=714

[alan_nc]

Here is another source for parts, just to get a comparison price.

http://www.boats.net/parts/search/Yamaha/parts.html

Alan

[tony27]

Pistons aren't available from them going off that, have a price in the high $180s & are obsolete so you can't order them

http://www.boats.net/parts/search/Yamaha/Motorcycle/1976/TZ250C/CRANK-PISTON/parts.html

[tony283]

Within the US the best place for all OEM Yamaha trials parts at discounted prices is Speed&Sport in PA. If you go to their web and select year and model you can get all the part numbers and then call them for pricing. I have used them during the course of my 30+ Yamaha rebuilds. www.yamatopdog.com

Tony

[billdapart]

WoW! Alan and Tony283 thanks for the links, as Tony27 pointed out those links wont help me much with a piston but for the rest of the build they are an absolute god-send! They look to use the exact same microfiche applet so I'm willing to bet they have the same supplier and prices on the available NOS parts. I'll have to try both and see who ships faster.

Tony27 thanks for the heads up, I actually had the wossner site up already when you posted that and will be the place that I go to in for the piston. I've already had REALLY great dealings with them and their VW pistons even back when I had to get them shipped across the pond.

So now that I am pulling the cases apart again and putting new bearings in and a new piston I think I'm good to go with the motor.

I'm currently looking at two things in the next part of the project. Fuel tank/seat and powdercoat/paint

What are you guys thoughts on this? I have an old tank which is in fair shape (one small ding) and has some rust inside. I also have no seat. I was thinking of either cleaning the tank with electrolosis and buying the majesty replica seat and making brackets or purchasing the sammy miller seat/tank combo. As I will be using this as a commuter part time to and from work and teaching my wife to ride motorcycles on it what do you think the more comfortable seat (to actually sit on ) would be?

Then what do you guys think about paint vs. powdercoat? I'm leaning towards powdercoat right now. Also I know i have to cut the swingarm away from the frame and I'm really not sure where to cut. Do I have to pry the frame away from the swingarm to get the blade in to cut the bolt? Or do i cut through the spacer/sleeve/bolt?

Thanks again all and sorry for my ridiculous posts.