Pulling things off cranks and pressing things on

[xwhatsit]

Hello,

Spot the difference:
<img src="http://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=121618&stc=1&d=1236331765" />

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]

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

[xwhatsit]

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 (http://www.tkrj.co.jp/) conrod kits (they do indeed have a kit for the XL250S/CB250RS (http://www.tkrj.co.jp/goods/m-BH0390A--428-.php), 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]

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]

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 :D)
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]

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]

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]

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]

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]

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 :D

[cowpoos]

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]

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 :D
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 :laugh:

[Ixion]

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.

[tychver]

Nah man the XR250R gearbox!

I'm keen on keeping mine 250cc eh.

[xwhatsit]

Well I bought the kit today. Let's see what it looks like.

[xwhatsit]

It's not a TKRJ kit, it's something called `Long (Since 1949)', which I've never heard of before and is impossible to Google for as all you turn up is results of `Long stroke conrod'.

They seem to be at great pains to point out that they're not a Chinese company.


BEWARE OF IMITATIONS!!

Please check embossment of "(L) MADE IN JAPAN" on Con' Rods as Sign of Original our products If No this Sign, they are all Imitations !

LONG PARTS CO., LTD.


and also:



Note: This is `real' Japanese product.
Make your advisable choice of "Long" !!

May just be anachronistic remnants of the 1970s/80s as the box looks like it's been sitting on the shelf that long.

Hope it's not a piece of crap.

The edges and casting marks on the outside of the rod -- I should smooth these out? With a file? With a hammer? With my forehead? How much would shot-peening cost, I wonder. I'll make some phone calls if I can find anybody who does it.

[Ocean1]

The edges and casting marks on the outside of the rod -- I should smooth these out? With a file? With a hammer? With my forehead? How much would shot-peening cost, I wonder. I'll make some phone calls if I can find anybody who does it.



If you think you're going to be pushing the rev's to 2% beyond the tensile limit of the rod then by all means spend fookin' hours linishing and polishing the beam faces. Otherwise you should leave the fucking thing alone, being especially careful you don't fuck with the bores in the process.

Seriously dude, concentrate on getting the crank assembled straight, clean and with zero damage to the bearing surfaces and you’ll be fine.

[xwhatsit]

Well I will be attaching a heavier piston to it (XT350 piston vs. CB250RS piston, the relative weights are posted somewhere), which will probably put some unusual stress on the rod. So I'd like to spend fookin' hours on stuff like this now so I don't have to spend more fookin' hours and heaps of money if it decides to part way with the crank :D

But yes -- what I think will be best is if (perhaps with the help of the generous Mr Ix) if we can assemble the crank and then take it to somebody to get it trued as best as possible. Probably be able to do it the same place who will assemble the oversized sleeve into the cylinder.

[Ocean1]

Well I will be attaching a heavier piston to it (XT350 piston vs. CB250RS piston, the relative weights are posted somewhere), which will probably put some unusual stress on the rod. So I'd like to spend fookin' hours on stuff like this now so I don't have to spend more fookin' hours and heaps of money if it decides to part way with the crank :D

But yes -- what I think will be best is if (perhaps with the help of the generous Mr Ix) if we can assemble the crank and then take it to somebody to get it trued as best as possible. Probably be able to do it the same place who will assemble the oversized sleeve into the cylinder.

OK. The objective is to remove any scratches or minor surface irregularities. They're stress risers, polishing them out increases very slightly the side loads at which the rod might fail. I don't think it'll make much difference to the ultimate tensile strength, and therefore won't help with the piston mass issue. Still, the material you'll remove from the rod might help offset it to a small degree.

I've never shot blasted rods, partly because I never had the gear to do it and partly because I could never see how micro-peening surface cracks closed would do much good. The prefered tool for polishing the beam faces is a linisher, not that uncommon. I'd use a die grinder to remove the bulk of the cast seam first, files or other cutting tools make relatively deep scratches which you'll just need to polish out anyway.

The surface in question extends from where the rod starts to get thicker towards each end, both convex surfaces, including most of the radius along the edge of the same stretch. Don't need to be morror-bright, just consistent, with the final polishing work done up the length of the rod, not across.

[xwhatsit]

Thanks very much for the information. I've looked up about die grinders -- my uncle possibly has one I could use. At least I think I saw something like that once in his garage. They look a bit like an industrial air-powered Dremel tool, but go much faster I expect?

Googling things and people say shot peening is a sort of case hardening; polishing the rod removes the case hardening so it needs to be shot peened to give it that back. But won't that take off the nice polish? I suppose everybody's got their own opinion, sounds like the `breaking in an engine' carry-on. Some Mini people seem to recommend radiusing (which I take it is smoothing out sharp edges and points) as being the most important, seems fairly dangerous for a clueless dickhead like me though.

[Ocean1]

I've looked up about die grinders -- my uncle possibly has one I could use. At least I think I saw something like that once in his garage. They look a bit like an industrial air-powered Dremel tool, but go much faster I expect?

Typically 10k to 25k rpm. Yep just a slightly heavier dremmel, in fact you could use a dremmel. In either case... *looks at pic of your rod* you might well get away with doing the whole job with one. One of the flappy emery paper (sandpaper) spoked type bits, a coarse one to start and something around 800 grit to complete should do it. Still need a bit of a hand polish to finish with.


Googling things and people say shot peening is a sort of case hardening; polishing the rod removes the case hardening so it needs to be shot peened to give it that back. But won't that take off the nice polish? I suppose everybody's got their own opinion, sounds like the `breaking in an engine' carry-on. Some Mini people seem to recommend radiusing (which I take it is smoothing out sharp edges and points) as being the most important, seems fairly dangerous for a clueless dickhead like me though.

Without knowing what your rod's made out of I'd be speculating about whatever hardening methods have been used. You can see it's been heated down it's length, except for the big-end but that may well have been an annealing process, (local reduction of hardening) to improve elasticity or ductility. Like I said, polishing it's not an automatic cure for any design shortfall, it's unlikely you'll actually make it weaker, but I'd shy away from attempts to mess with the steel's temper.

Any hardening resulting from shot-blasting will not be case hardening, which is a process involving the penetration of carbon into the surface of an otherwise non carbon or low carbon steel, maybe the top 10thou. Shot blasting might work harden the surface, possible in just some alloys and certainly in carbon steels. While the rod's almost certainly a carbon steel, the effect of shot blasting any given part/alloy can only be ascertained by emperical methods. If you can find evidence of improved strength from actual experimental results then by all means use it. Otherwise I'd say the benefits are, at best, unknown.

[Ixion]

Thanks very much for the information. I've looked up about die grinders -- my uncle possibly has one I could use. At least I think I saw something like that once in his garage. They look a bit like an industrial air-powered Dremel tool, but go much faster I expect?

G...
I got one. Y need the compressor too of course! Vicious thugs of things.

PM me when you are ready to do something and we'll work it out.

[xwhatsit]

Cheers Ix!

By the way, just doing some scratching around as one does at 2.30am, I think I'm on the right track with these calculations, anyway:

XT350 piston is 369 grams compared to CB250RS piston 329 grams. Given a stroke of 57.8mm, a rod length of about 12cm (dunno, just pulled that out of my hat), redline of 9500rpm, this means it's pulling 2210 G at TDC. I think this is the worry, not BDC (even though G-force here is much higher, but it's compressive forces...?)

So, 0.329 grams * 2210 * 9.81 = 7133 N.

Compared to 0.369 * 2210 * 9.81 = 8000 N.

So, working backwards, 7133 / (0.369 * 9.81) = 1971 G

To reduce G-force at TDC down to 1971 G, run at 8973rpm instead of 9500rpm.

500rpm is sweet f-all. Answer to not blowing up engine: don't redline it!

Funny that.

Even with the stock revvy 250 engine it's not particularly helpful (in terms of forward progress) to redline it anyway (max power coming at 8500rpm, max torque at 8000rpm).

EDIT: Just realised redline is actually 9000rpm not 9500rpm. But it works out the same anyway -- reduce redline by ~500rpm to compensate for the extra 40 grams.