Got needle bearing to replace bush but....

  • Thread starter go you good thing
  • Start date

go you good thing

After several attempts I now have a bearing to replace the brass bush in the conrod.

My first attempt (pictured in the middle below) fit the conrod but I could not get the pin in the hole. This came as a spare part from the new shipment of 70cc china motors that have them included.

I went to a specialist bearing supplier and after measuring my bush/pin got one that is 12mm wide, has a 10mm center hole and 14mm outer diameter.

The first one (in the middle) has exposed needles so the hole in the top of the conrod would feed oil to it when it us running but wont fit:(

The bearing on the right from my supplier should fit but has a solid outer casing so oil will not get down from the top to lubricate it.

As you can see by the original bush (on the left) the hole continues through it to lube the pin.

My question is will this bearing get oil? I will fully grease it up before installation and their is a little play when the pin is installed as with the bush but is this going to be ok or is it going to seize after a while??? The bearing guy said that it should be ok.

Any suggestions would be appreciated as I want to install it asap.


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I may be wrong but I believe the entire crankcase and area under the piston fills
with fuel/oil vapors before being routed into the combustion chamber through the transfer ports...This should provide the necessary lube for the internals and bearings. As far as the bearing installation I am not sure how but I would be interested in doing a performance upgrade like that too so I'll see if anybody else chimes in.
Thanks andyinchville1,

I think you are right with the vapours but I wonder how much pressure it is under to force it in the bearing??

As for some instruction on how to do it, I found this link while I was looking:

I found heating up the conrod with a small blow torch helped getting it out.

I have also read here that puting the bearing in the freezer and heating up the conrod is the way to get it in. Guess I'll find out soon:D
I would fit the middle one and if you have a 1/4"drill motor, hack saw and some basic skills I will tell you how.
I am very interested to see how this works out.
Just a thought here (NOT advice, as I don't know) but on that third from the left bearing, couldn't you drill a small hole, or series of 3 holes, around the casing (similar to the brass bushing), at say, 120 degrees spacing from each other to provide openings for lubrication? Heck maybe even add two more small bores at similar locations on con. rod as well...?
Please keep us updated on this as it would be great to upgrade/improve my 80cc in this way...:cool:
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oh wait...

That might not work as the drilling would create a small burr on the bearing side of the casing, thereby creating premature wear on the bearing surfaces...]
Hmmm... I'll have to think some more. Anyone else have thoughts on this?
Then again, you might be able to get a needle file down into the bore, at an angle, from the top side, to cut down the burr. You'd have to make absolutely sure there were NO residual filings in the bearing assy. but that might be a way of making it work...
Thanks for your thoughts guys.

I would fit the middle one and if you have a 1/4"drill motor, hack saw and some basic skills I will tell you how.

Dang I don't have a drill and a hack saw.:D

That might not work as the drilling would create a small burr on the bearing side of the casing, thereby creating premature wear on the bearing surfaces...]
Hmmm... I'll have to think some more. Anyone else have thoughts on this?

I had thought about this but was concerned about a burr and their is a bearing race inside holding the bearings equally apart so I may bend this if the drill went in too far. This bearing is very small so a file may not be possible to use with my eyesight:eek:

Another method might be to get a dremel or grinder and make a slot type hole in the outer casing. That way the burr may not happen or I could try to bend any thin metal up and out. What do you think?
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I just had another thought.....

I could grind 2 or three little slots on both ends of the bearing cylinder across the top and bottom rim edges. That way when installed it would get vapors entering from both sides and the hole in the top would not be required....mmmm.:confused:
I asked augi to check the wrist pin clearance on that new Dax motor he has the top-end off of. This would be a good thing to know. I think it will be .001"~.0015".
The pin clearance will be effected by the amount of interference fit that the Torrington bearing has when installed into the rod's small end. Too tight a fit and the pin will not go home. Your supplier should be able to tell you what the interference is...prolly < .002". If this bearing is pressed in w/o preheating the rod's small end the hardened outer shell will crush enough to lock-up the tiny rollers. Not a good thing.
Pre-heat the rod end with a low flame from a propane torch. The heat must get into the internal mass so the bush hole will open. The Torrington should just drop in when it comes out of the freezer(do not let it fall through the hole). Cool it off with several squirts from a pump oil can.

To open up the bush hole if needed? Use the non-existant 1/4" drill with some carborundum cloth wrapped tightly around a 1/4"split shaft, it should fit the hole snugly. Take your time and check dimention often with atleast a good dial caliper. The other bearing could be fitted this way also.
Did you notice that the rod has a strike of copper plating? This should be removed from the bore it the roller bearing that came with the motor is used because it will start smearing as it gets on the rollers. Not a biggie but even if this bearing proper fit, a light cleaning off of the copper should be done.
I have several air and electric die grinders here as well as a decent selection of flap wheels. A small new flap wheel and the air die grinder running at 7000~10,000rpm would make quick accurate work of this.

I would not notch the ends of the Torrington. If I used this bearing a notch would be made to meet the top hole of the rod. A thin sharp scribe could be used to pick out burrs. Blow air on it as you use prolly a cut-off wheel on the Dremal to cut a lubricating notch. Might even hold the Torrington in a shallow dish of water. The point is that heat will generate a large burr that will be next to impossible to remove. So it must be done slow 'n cool to avoid a burr. The top hole on the rod could be chamfered with a 1/4" drill bit to help collect oil. Just a light chamfer mind you.

Torrington bearings are normally used on the lightly loaded ends of gear shafts and run in an oil bath. The other end of the gear shaft will had a large ball bearing. This bearing might work out for ya.

NOTE: I raced Mercury outboard hydroplane boats while in high school. Played 'n raced two stroke dirt bikes in the '70s and helped a friend of mine maintain his son's TZ250cc Yamaha road race motorcycle for two seasons. Lots of tear downs with the Yamadog. So yes, I have done my share of stroker work.