Pulling things off cranks and pressing things on

**xwhatsit** · 6th March 2009, 21:32

Hello,

Spot the difference:

Our main problem is part #5 on the left, #6 on the right. On the CB250RS crank, it's a sprocket, for the chain-driven balancers. On the XR250R crank, it's a gear, for the single gear-driven balancer.

So I'm putting a XR250R 6-speed gearbox into a CB250RS engine, which necessitates using a gear-driven balancer to get things out of the way (plus -- ask any RS owner -- adjusting the chain for the balancers is the biggest pain in the arse about them). A cheap NOS CB250 crank has come up on Tardme (no bastard is touching it -- you all feck off, you hear!), they want more than twice the price for an XR250R crank... can we simply press the sprocket off and press the gear on (I have a rooted XR250R crank)?

Which sort of place will help me with this?

Thanks for all advice.

**Ixion** · 7th March 2009, 12:22

I got a 20 tonne press and some honky big extractors.

**xwhatsit** · 7th March 2009, 12:32

Originally Posted by Ixion

I got a 20 tonne press and some honky big extractors.

Fully sick, bro.

Actually I've re-read the Tardme auction and it says `conrod kit'. Now I'm 99% sure there was never a conrod kit, Honda only sold complete cranks. So that's why I thought it was a complete crankshaft/conrod everything.

If it is, for some strange reason, a `conrod kit' only, given that the problem with my existing XR250R crank is play in the conrod (big end bearing), will this fix it? Is there anything else that wears out that I need to worry about?

EDIT: Yes well I've firmly convinced myself that it's one of these TKRJ conrod kits (they do indeed have a kit for the XL250S/CB250RS, and I saw another old auction on Tardme selling it for a similar price). They come with the big-end bearings. I hope they're good quality -- never heard of them before, hopefully better than an old OEM one anyway.

Is your gear capable of pulling apart and putting back pressed cranks like this, Ixion? Or do I need a specialist?

**Ixion** · 7th March 2009, 13:58

It's capable of pulling them apart and putting them back together. Whether I (or you) am capable of truing them up is another matter. I've done it on Briddish singles, but I imagine their tolerances were more generous than high revving Jppas. But it's largely just a matter of patience - something I possess very little of.

**hmmmnz** · 7th March 2009, 14:27

ive done it very dodgily on a ag175 with just a big arse drift and a small sledge hammer, new crank pin in and big hammer, then trued it up using a peice of wood and a nail (using the big arse hammer to adjust

)
it took a bit of time and is no way particulary accurate, but that particular bike is still running sweet 10 years later,
i'd say your best bet is press it out the old and press in the new crank pin on one side of the crank, then take the new con rod ect to an engineering shop and let them do the rest, it should only take 10 or 15mins for any one who knows what they are doing

**Ocean1** · 7th March 2009, 15:13

Originally Posted by xwhatsit

If it is, for some strange reason, a `conrod kit' only, given that the problem with my existing XR250R crank is play in the conrod (big end bearing), will this fix it? Is there anything else that wears out that I need to worry about?

Yup, that'll do it.

The journal fit's not actually that tight, just awkward to jig up to support the crank-halves. If you don't get the press force lined up reasonably well over the big-end you can distort the journal bores, so it pays to piss around with packers getting it right.

Note the oil port on the journal, make sure it goes back facing the same way. I press the cranks back together using a lathe, the tailstock is strong enough to do it and you get to stop occasionally to check the crank alignment with a dial gauge, (and the final side clearance in some cases) and "adjust" with a special (copper & hide) tool.

The difference between getting it right and not is noticable. I once stripped an XR500 that had been out by a mere 10thou, after the rebuild it was way smoother.

**bsasuper** · 7th March 2009, 15:14

If I remember correctly the sprocket/gear is on a taper so putting it on will be no problem but getting it off could be.

**Motu** · 7th March 2009, 15:24

The real tool for the job is a kind of ''pot'' the flywheels fit into and hold them in alignment while the pin is pressed in and out....getting end float correct of course.Using the jig means minimal corrections with a copper or rawhide hammer.I have a jig for the smaller (XR200,TLR200) cranks,but doubt it would fit the 250.

Honda only sold complete cranks (for fucks sake,why?) I presume after market rod kits are available....it'd be a no brainer.

**xwhatsit** · 7th March 2009, 15:29

Good-o then. I might purchase this rod then and when I get everything else I need sorted then I'll look into fitting it.

Thanks for all the information!

Did a search for TKRJ stuff, a lot of people here seem to say reasonable things about their pistons, nobody mentioned the conrods. I suppose as long as it's at least as good as OEM then that's great.

**tychver** · 7th March 2009, 19:21

Tell us how this goes man. I wana do the same conversion later.

Meanwhile, have xwhatsit have you noticed the CB250RS plus spare bike plus loads of spares in ChCh on trademe for $1300? If I get 1300 before the auction closes I'm so getting that

**cowpoos** · 7th March 2009, 19:30

Originally Posted by Ixion

Whether I (or you) am capable of truing them up is another matter

Dial gauge and a acurate verneir caliper should see you right...

**xwhatsit** · 7th March 2009, 21:43

Originally Posted by tychver

Tell us how this goes man. I wana do the same conversion later.

Meanwhile, have xwhatsit have you noticed the CB250RS plus spare bike plus loads of spares in ChCh on trademe for $1300? If I get 1300 before the auction closes I'm so getting that

Heh. You're talking about the XT350 piston conversion? There's a chap in Germany who posts on here who's nearly finished already.

I've got enough CB250RS crap lol -- I've had two spares bikes and a have a complete rolling chassis left I plan to convert into a bucket racer with a suitable engine and boxes of other crap. If you ever need any indicators, headlights, that sort of crap, I'm your guy

**Ixion** · 7th March 2009, 22:19

Originally Posted by cowpoos

Dial gauge and a acurate verneir caliper should see you right...

Yeah got those. And the centres n stuff. Know how to do it , done it in the past, but it can be a pain in the neck process. Some are real easy, others, not. Same with splitting them, some can be a real prick to jig up. Not so bad if the conrods scrap cos then you can support the crank on that which gives you the third point.

Actually that one may be an easy one cos it looks like the crank pin isn't stepped. So the old one can be pressed right through the web , meaning the crank doesn't have to be supported by the upper web, which is always the pain. Have to pull the main bearings off though which probably means pulling that gear/sprocket off anyway.