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- Jun 13, 2007
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- south east WA Australia
after this thread viewtopic.php?f=5&t=9721&hilit=crank+oil+jet+bushmechanic
Taffy wanted me to write it up proper cause it was hard to read/find and I got some messages about what balance factor to use and how to calculate it, it’s all in the text in Weeds gallery "tuning for speed"
http://www.husaberg.org/gallery/v/Membe ... ?g2_page=4
so dunno if its easier to read but its written up proper
Hard to say what will work and how to get a certain Balance Factor so I’m not going to say what you should use I thought 0.75 was good but I’m running a bigger piston now which takes it back down to 0.55 or thereabouts and it feels better at low RPMS. Will have more to say about high RPMs and the new engine in another thread but you have to try stuff out and see what you like just like Simon said.
FWIW you can add about a 70gm weight per side opposite the pin (total 140gm) to the 628 cranks by welding on the SS weights. I added about 35gm/side and ground a bit off the crank pork chops near the pin. I found my 628 crank needs 0.6mm or more axial play on the big end with the welded on weights, tried 0.5mm rod big end play like stock but it was too tight. The added weight makes the crank spread more since there is about an extra 500kgs on it at 8000rpm. I have the crank axial float in the main bearings set larger too at 0.65mm instead of 0.55mm
Lots of people want to know what to do to weld a crankpin so instead of repeating messages I’ll put it here. There are a lot of ways to do this and im not pretending that my way is the best. If anyone wants to suggest a different way go right ahead I’d like to learn something new.
I welded a few crankpins this week so while its fresh heres what I do:
To rebuild a crank you need a very rigid press not necessarily a strong hydraulic ram about 20T is enough even for the jap cranks. 8 ton or so is enough for the berg cranks. The reason you need a rigid press is the static coeff friction is greater than dynamic so it takes less force to keep the pin moving than it does to move it.
With a flexy press it loads up all the flimsy steel and bends say 4mm, when the pin starts to move it goes bang and jumps 2-3mm at a time pushed along by all the flexed up steel in the schitty frame. You can't get anything right with one of those. In a rigid press the pin just creaks and jiggles its way in a small amount at a time because the flex of the press is only 0.1 or 0.2mm so that’s as far as the pin cam move when it jumps.
Before pressing out the pin make a few scribe marks across the flywheels to help align it later. To press out a pin the tried & true method is to cut through the rod and crankpin with a 9" grinder so you don't ovalise the holes in the flywheels when pushing out the pin. I make up a special backer plate and packers if necessary for every crank so I don't have to waste a rod every time. If the rods shagged just cut it its much easier.
When its apart measure the bejesus out of everything for ovalised holes or too big IDs will put up some figures on ideal interference fits when I can find em. You can get oversized pins but I don't know where from, ALPHA bearings in the UK or some modded jawa pins maybe.
Putting it back together is easy if you make sure the 2 webs or flywheels aren’t twisted too far, press it on 10mm or so and then check and adjust. The berg cranks can be adjusted for twist when fully pressed together, most of the jap cranks can't so you have to get it right on the way in. you could/should make up a jig to hold the crank webs in alignment while pressing together but its not necessary if you're careful. Heating one bit and freezing the other bit makes it easier too.
I’ve started over truing the cranks that I weld. That is instead of spread opposite the pin like they are when they come out of a bike you can squeeze the flywheels or webs together opposite the pin so runout is 0.05mm or so between centres. Then when it spreads the idea is its closer to being right. to measure runout I have a jig to run the crank on ball bearings where the mains go and this is more correct particularly if the centres are damaged or not on centre but this method always gives a better reading than between centres because the runout bit is closer to where you're supporting the crank. So if the centres are ok I use the lathe and run the crank between centres because it gives a better result.
I used to use a jig to hold the cranks still and true while I welded the pins but they always moved a bit its easier to make 4 small cold tack welds to hold the pin and use these tack welds to true the crank again if needed, i.e. if you want to close up the crank re-weld the tack near where it needs closing up. If its twisted though you need to grind out the welds and start again. If its how you want it after these tacks have cooled it won't move when you do the final welds. I found if I do the final welds and its gone out of true there is no point re truing it in the press because once in the bike it just goes back to where it was after I finished welding it.
The tack welds need to be fairly slow making the puddle and then drop a heap of stainless filler in, if you don't use enough it will crack from embrittlement.
For the main welds I preheat the crank to 150degC and use pulsed DC, I try to keep the welds quite small it looks neater that way though bigger is stronger. Do small tacks and alternate from once side of the crankpin to the other. It is possible to get the crank too hot during welding after the preheat so watch it, the quicker you are at dropping the filler in the better as it reduces embrittlement. you want to add as little heat as possible after dropping the filler in again to reduce embritlement.
I put tape over the bearing inners and a steel pipe over that to protect them
Check the welds clear the counter balancer if you’re still running one and on the other side they need to clear the main bearing spigot in the case.
hope that helps someone 8O
A great tip on getting the crank end float right from KTM talk is to remove all the shims that you can from the crank and shim up the float with the bearing outer in the case.
Taffy wanted me to write it up proper cause it was hard to read/find and I got some messages about what balance factor to use and how to calculate it, it’s all in the text in Weeds gallery "tuning for speed"
http://www.husaberg.org/gallery/v/Membe ... ?g2_page=4
so dunno if its easier to read but its written up proper
Hard to say what will work and how to get a certain Balance Factor so I’m not going to say what you should use I thought 0.75 was good but I’m running a bigger piston now which takes it back down to 0.55 or thereabouts and it feels better at low RPMS. Will have more to say about high RPMs and the new engine in another thread but you have to try stuff out and see what you like just like Simon said.
FWIW you can add about a 70gm weight per side opposite the pin (total 140gm) to the 628 cranks by welding on the SS weights. I added about 35gm/side and ground a bit off the crank pork chops near the pin. I found my 628 crank needs 0.6mm or more axial play on the big end with the welded on weights, tried 0.5mm rod big end play like stock but it was too tight. The added weight makes the crank spread more since there is about an extra 500kgs on it at 8000rpm. I have the crank axial float in the main bearings set larger too at 0.65mm instead of 0.55mm
Lots of people want to know what to do to weld a crankpin so instead of repeating messages I’ll put it here. There are a lot of ways to do this and im not pretending that my way is the best. If anyone wants to suggest a different way go right ahead I’d like to learn something new.
I welded a few crankpins this week so while its fresh heres what I do:
To rebuild a crank you need a very rigid press not necessarily a strong hydraulic ram about 20T is enough even for the jap cranks. 8 ton or so is enough for the berg cranks. The reason you need a rigid press is the static coeff friction is greater than dynamic so it takes less force to keep the pin moving than it does to move it.
With a flexy press it loads up all the flimsy steel and bends say 4mm, when the pin starts to move it goes bang and jumps 2-3mm at a time pushed along by all the flexed up steel in the schitty frame. You can't get anything right with one of those. In a rigid press the pin just creaks and jiggles its way in a small amount at a time because the flex of the press is only 0.1 or 0.2mm so that’s as far as the pin cam move when it jumps.
Before pressing out the pin make a few scribe marks across the flywheels to help align it later. To press out a pin the tried & true method is to cut through the rod and crankpin with a 9" grinder so you don't ovalise the holes in the flywheels when pushing out the pin. I make up a special backer plate and packers if necessary for every crank so I don't have to waste a rod every time. If the rods shagged just cut it its much easier.
When its apart measure the bejesus out of everything for ovalised holes or too big IDs will put up some figures on ideal interference fits when I can find em. You can get oversized pins but I don't know where from, ALPHA bearings in the UK or some modded jawa pins maybe.
Putting it back together is easy if you make sure the 2 webs or flywheels aren’t twisted too far, press it on 10mm or so and then check and adjust. The berg cranks can be adjusted for twist when fully pressed together, most of the jap cranks can't so you have to get it right on the way in. you could/should make up a jig to hold the crank webs in alignment while pressing together but its not necessary if you're careful. Heating one bit and freezing the other bit makes it easier too.
I’ve started over truing the cranks that I weld. That is instead of spread opposite the pin like they are when they come out of a bike you can squeeze the flywheels or webs together opposite the pin so runout is 0.05mm or so between centres. Then when it spreads the idea is its closer to being right. to measure runout I have a jig to run the crank on ball bearings where the mains go and this is more correct particularly if the centres are damaged or not on centre but this method always gives a better reading than between centres because the runout bit is closer to where you're supporting the crank. So if the centres are ok I use the lathe and run the crank between centres because it gives a better result.
I used to use a jig to hold the cranks still and true while I welded the pins but they always moved a bit its easier to make 4 small cold tack welds to hold the pin and use these tack welds to true the crank again if needed, i.e. if you want to close up the crank re-weld the tack near where it needs closing up. If its twisted though you need to grind out the welds and start again. If its how you want it after these tacks have cooled it won't move when you do the final welds. I found if I do the final welds and its gone out of true there is no point re truing it in the press because once in the bike it just goes back to where it was after I finished welding it.
The tack welds need to be fairly slow making the puddle and then drop a heap of stainless filler in, if you don't use enough it will crack from embrittlement.
For the main welds I preheat the crank to 150degC and use pulsed DC, I try to keep the welds quite small it looks neater that way though bigger is stronger. Do small tacks and alternate from once side of the crankpin to the other. It is possible to get the crank too hot during welding after the preheat so watch it, the quicker you are at dropping the filler in the better as it reduces embrittlement. you want to add as little heat as possible after dropping the filler in again to reduce embritlement.
I put tape over the bearing inners and a steel pipe over that to protect them
Check the welds clear the counter balancer if you’re still running one and on the other side they need to clear the main bearing spigot in the case.
hope that helps someone 8O
A great tip on getting the crank end float right from KTM talk is to remove all the shims that you can from the crank and shim up the float with the bearing outer in the case.
