two stroke Rotax 123 rebuild. novice needs help.

[Darkstar82]

As some may be aware im attempting to learn how to rebuild my engine, its a rotax 123. ive done plenty of top ends but never ventured this far.

got the case split, new bearings in, new seals, the cranks back in place and the engine back together but ive noticed this on a diagram...

https://www.ultimateparts.net/ri.php?f=..%2Fimages%2Fcategories%2F17814.jpg&h=250


item 3, two metal spacers. Theres no place for spacers on the external part of the casing so im presuming the diagram means they go between the bearing and the caseing.

Are these essential as I dont appear to have any? there is no side movement on the crank, nor does it feel like its rubbing, its abit stiffer than previous but new bearings and minimal oil would account for that.

as always, thanks for your advice,

[-]

No experience of Rotax engines, maybe a Kart forum might have more experience.

What are part 3 described as? Which numbers are oil seals?
It seems odd to have 2 spacers, both next to each other, why not just make 1 thicker spacer?
____________________
TZR250 2MA road, TZR250 1KT road, TZR250 2MA race, TDR250, YZF-750R Boost colours.
Jaguar S Type 3.0 V6 Sport R, VW Transporter T5 GP LWB Shuttle 140ps DSG.

[Darkstar82]

[Hugh Farking Cant]

Shims for setting crankshaft/crankcase endfloat. ?

May or may not be required in combination depending on c/case; crank fit. They will be different thicknesses.

[Kickstart]

Hi

Looking at a 123 parts list (older one for the Sintesi) there is one part number 827410 which is nearest the con rod and labelled a 'distance ring'. Another part beside that is labelled a shim, available in 4 different sizes. 944582, 944583, 944584 an 944586, being respectively sized 0.3, 0.1, 0.5 and 0.2.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Pete.]

[Kickstart]

[Darkstar82]

now, before you laugh, my artistic side never really took off so be prepared.





If you could run your eye over this image Ive lovingly created after literally minutes of slaving away, and confirm Ive got it right that would be grand,

https://i61.tinypic.com/5xlrvc.jpg

then i can go cry in to a pillow as i don't have a bearing puller and will have to either buy one or take the entire engine back to the sodding garage to have it pulled. again.

also Ive got a small pile of metal shims, i haven't got a decent manual hence Ive no idea of the diameters and measurements of the components beyond going "looks about right..." and trying it.

the joy.

[Kickstart]

Hi

interesting that the early parts list has an extra part, and has the spacers on the other side of the main bearing compared to the later parts list and your photos.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Pete.]

I'll be honest with you - I see no good reason to have those spacers on a little stroker with a roller bearing crank if the bearing is a tight fit. I can't imagine how one would go about deciding which sizes to fit without some serious measuring equipment and even then I doubt you could get it right.

Personally, I would build the thing and forget about them.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[bladerunner]

Indeed it's a spacer shim and only needed if the end float is more than 0.27mm or whatever is specified in the manual.....been a long time since I rebuilt 1. The japs just generally build an engine that allows the build up of tolerance ....the Italians tend to use the spacers and different size gaskets to build a motor to spec....the japs use the same options only on more race type engines for barrel spacers only! Ie rgv250 has different thickness base gaskets but nothing on the big end or crank side but uses shims on the little end bearing to hold the con rod straight...the amount of con rod and crank float will strike fear into Yamaha and Honda owners who are used to shims on the con rod to crank web spacers! And the use of no head gasket but O ring type head sealing is also something that needs careful attention on the little Italian motors like the RS50 and mito motors....std race practice from those in the know as well as squish gap and head volume.....the Italians do know how to build a motor.....if the owner knows the same can be a different matter! But once you know what's important and it's not hard to measure....you'll feel sorry for the owners of the latest greatest <500cc owners!
____________________
Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's

[Pete.]

[bladerunner]

Good point!
____________________
Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's

[Darkstar82]

okeydokey, well, my thanks to all of you bloody useful people as usual.

I am going to continue without the spacers. The new bearings are a firm fit. hopefully I will be ok.