crank questions

[Rabbitist]

hey so ive just pressed the crank pin out from my crank after a big end bearing failure (part of the needle roller cage made a key way in my piston). anyway im after the distance between the two sides of the cranks so i can use slip gauges when pressing the new pin in.. failing that im after the amount of float the rod has between the side of the crank and the white metal coated thrust washers? is it possibe to use feeler gauges when pressing the new pin in to set the float? also i am thinking that liquid nitrogen is an option to seat one side of the crank pin as it would make it that little bit easier to press.. i am planning on turning a bit of bar to use as a dowel to align the two parts of the crank roughly before pressing then trueing.. the dimensions from one side to the other are 150 microns difference the fly wheel side measures 22.20mm and the other side measures 22.05 there is no problem with turning a stepped dowel but is it worth using the dowel holes or can they effectively be a way out? (are the crank sides machined/drilled together making them true?) also does around 12 tonne sound about right as that is what it hit before the dowel moved.. are the cranks frozen when made or just pressed.. if you have any of the information above please share as it would be extremely appreciated thanks luke

[Neil E.]

I have not pressed any cranks myself, but the concept is simple enough. I would have thought a higher tonnage is required. The crank wheel and stub shaft is normally one machined piece. I have trued several cranks and prefer using a roller stand instead of lathe centers.

Usually you measure the width of the crank "cheeks" first and then duplicate this measurement with your new parts. I expect the crank itself shoulders on the primary side ball bearing and then there is a gap to the ignition side bearing. You could measure the cases to get the maximum space dimension, then stay a bit under this.

I'm not sure how you would position the stepped dowels. I guess these are meant to be spacers on each side of the rod so you can't pinch the rod during assembly. I would be worried about overshooting and not having enough side play for the rod. It should look right with the pin flush to each crank cheek.

Warming/cooling the parts sounds good, but does this give you enough working time? The change in force due to temperature change might not be as predictable as pressing at room temperature.

[Neil E.]

I think I understand your dowels. You want to use the crank holes to guide the alignment process. The usual method is to have jigs that guide on the OD of the crank wheels. I think "squareness" is more important to maintain the quality of the crank bores. You can smack the crank to align it radially (pivoting the crank cheek about the pin).

[GMP]

Rabbitist,

There used to be a link to a GasGas factory engine shop manual, but I see for some reason it is gone. I have a copy (PDF) I can email to you which should have all the info you need. PM me your email address.

[hillbilly]

hi there sorry cant help you with your crank rebuild issues but hope you might be able to help me with a quick query. Just stripped my 300 to replace failed right hand main bearing , crank seal almost non existent and not sure which way round to put the new seal in? Maunal states lip facing outwards, Gas gas UK say main lip inwards with flat face of seal facing out and small lip on outside. confused :S Which way round was yours when you stripped it, hope you can help me thanks. Good luck with you crank hope you figure it out! Cheers simon....
p.s
where are you in the UK not many of us on the site.

[Rabbitist]

Mine were the same way gas gas uk reccomend however I can't see it mattering too much.. Some say the other way as the force is sucking rather than blowing but in reality I can't see it matters to much just as long as theres a seal I'm sure someone will correct me if I'm wrong.

[Rabbitist]

I'm located in lincoln mate. The dowels are simply to get the crank roughly lined up before knocking true

[GMP]

Luke,

I just sent you the manual, but the short answer for the big end side clearance is .8mm.

[PEB]

Gas gas UK say main lip inwards with flat face of seal facing out and small lip on outside

This is the way they are installed from the factory.

[GMP]

Just like the ignition side and every other seal on the bike, and other bikes for that matter.