2 Stroke crank rebuild

[Martay]

Hi,
My friend is currently using my scooter (Honda SH50 City Express) and has informed me the big end or mains are rumbling pretty badly.
I have a spare engine here which has suffered the same fate. I think its quite a common problem?
Anywho, i decided i would embark on stripping the spare engine down, firstly for something to do, and secondly so i can steal the crank from it. Ive never done this before, but ive seperated the cases with the aid of beating the hell out of it
I got the crank out the same way, putting a nut on the threaded end and beating it into next week. Ive tapped the bearing out of the case to find they run the same numbers as the wheel bearings i fitted to my dads trailer! I have a problem of one bearing is stuck on the crank and i cant see a sensible way of removing it without wrecking the crank.
Anywho, the big end has no play in it, so im wondering weather to get it rebuilt with a new con rod, big end and mains or weather to just bung it in as is?
A new con rod kit is £35 from wemoto; https://www.wemoto.com/bikes/honda/sh_50_e_h_k_m_p_dp_city_express/85-96/picture/con_rod_kit/
Replacement main bearings i will get from a local supplier, as they are alot cheaper than the £25 EACH from ebay / wemoto.
Advice please peeps
Ta
____________________
Eat well, poo hard
Drives: Cavalier 2.0 16v
Rides: Slightly ratted Honda City Express

[steven_191]

Sounds cheap enough to do the whole lot. Not sure if theres any balancing required but I had my crank rebuilt as part of some other engine work so didn't do it myself.

If you've not already destroyed the cases you would be better off to repair the engine you have already stripped the when it comes to the bike its a quick engine swap

Try heating up the bearing on the crank and see if you can get it off like that. As I say, I had this work done by someone, including removing the bearing.

[Martay]

I didnt damage the casings (surprisingly!) but the transmission is all part of one side. The rear reduction gearbox / clutch is SO noisy i figured it was shot too. I suppose i could strip that out too and swap but its turning into more of a mission than id hoped.
Thanks
____________________
Eat well, poo hard
Drives: Cavalier 2.0 16v
Rides: Slightly ratted Honda City Express

[jimmyRS]

by the sounds of it you haven't got the right tools or methods to rebuild a crank properly and safely with the new conrod kit so alternatively id suggest buying a new crank or leaving it as it is, providing the play isnt bad.

as for reassembly, put the main bearings (buy steel caged ones as opposed to plastic, tend to last longer in my experience) in the crank casing or on the shaft, i personally think its better to put them on the shaft first then slide the crank in. To make fitting the crank easier, freeze it, and warm up the engine casings before you put the crank in. Had to do this when i rebuilt a 2 stroke am6 engine, made it a hell of a lot easier.

It should slot in nicely, still with a bit of effort though

Good luck!

[YBR Ric]

You may be able to purchase the main bearings cheaper than advertised on Wemoto, but are they EXACTLY the same bearings as sold by Wemoto?

They may have the identical bearing sizes shown on the outer race, but what about the running clearance between the inner and outer race?

The manual might stipulate anything between a C2 up to a C4 clearance is required. Fit the wrong one and it will either run too tight and fail, or be too loose and have a very short working life.
Double check the bearing specifications and ensure your bearing supplier sells you exactly what is required.

However if this is a common problem specific to this engine, there is an outside chance the manufacturer has made an incorrect specification.
It might be worth an engineers opinion as to why the bearing itself failed, they might suggest a different clearance to rectify the problem.

[Teflon-Mike]

The crank pin will conventionally be on interference fit tapers into the flywheels, and will generally take a ton or two of 'force to seperate.
Certainly more than beating the bugger with a 12oz hammer can apply!
Usually 'pressed' apart in hydraulic engineering press, then re-assembled the same way, carefully 'jigged' to make sure that the two ends of the main-shaft are rinning concentric.
Any small mis-alignment of the main-shafts means that one end will 'wobble' in relation to the other, or the crank-pin will be twisted by the shafts being forced to run in-line by the bearings in the assembled cases
THEN the flywheels are 'balenced' as an assembly with the new con-rod and bearings on it, so that when fitted and running, the thing doesn't shake itself apart again.
Ie: specialist operation, & seen 'quoted' prices ranging from about £75 (I presume without parts) to over £200 depending on the crank in question.

As for the main bearings; common for bearings supplied from 'catalogue' to be an awful lot more expensive than supplied by bearing catalogue number from a bearing stockist.

They OUGHT to be the 'same' part, if they have the same bearing number on them!

Reason that as supplied through a motorcycle outlet, is that the bearings are re-packaged in smaller quantities and re-numbered to the part number used by the motorcycle manufacturer, rather than the bearing maker. Then, rather than passing through possibly only one or two 'handlers' from the maker to the customer; so bearing maker to distributor, distributor to local whole-saler; whole-saler to 'stockist' each putting thier handling costs and profit on the part; they go from maker, to distributor, to whole-saler, to re-packager, to MOTRCYCLE PART distributor, to M/C whole-saler, to motorcycle part retailer....... EACH putting thier handling costs and profit on, and handling smaller volumes, adding more for the trouble.....

JUST so you can say "I want a Main Bearing for a 2004 Honda Moped" rather than say, I need a 25/12x10 TKN123-756B...

Knowledge is POWER, in this case the power to save money!

Being able to order by the end product, rather than the piece part spec can be an expensive convenience.

Wheel-Bearings, for my '81 Montesa, (about five years ago) bought from the UK Importers, Jim Sandifiords, packaged through the Honda parts network, were something like £30 a pair, plus seals. Bought by bearing number from local bearing stockist, were £30 the set... BOTH wheels AND seals.

BUT, I had to strip the hubs, before I could find the Bearing Number, and HOPE they weren't so rusted as to be illegible, and THEN take them to the stockist, and hope he didn't have to order them in, and wait however long before I could put the bike back together....
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'