wrist pin needle bearing lubrication holes

sun

New Member
Apr 7, 2008
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Hi, first post here, great forum. I am rebuilding a new 70cc boygofast China motor and want to drill lubrication holes in the top of the con-rod to help lube the needle bearing. My understanding is that some motors have these holes but mine doesn't. Without having seen one with holes, I am planning to drill three 5/64" inch holes, one on top and others 45 degrees offset to each side.

Does this sound right and if not what sizes and positions are recommended. Sorry if this is posted somewhere, search yielded no results this time.

Thanks:)
 

deacon

minor bike philosopher
Jan 15, 2008
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I can't help you but i never saw it posted and have no idea what to tell you. Please don't worry too much about asking questions that have already been asked, we do it all the time. If there is a detailed answer someone might give you the url to it, but otherwise they will jump right in to help.

This sounds like a norman or bikeguy joe's kind of question to answer.
 

Norman

LORD VADER Moderator
Staff member
Jan 16, 2008
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What type of nedle bearng you going to use caged or the type that are in a can I call torrington needle bearings.
The caged shouldn't need extra oiling holes needle bearings are a low friction bearing and have planty of room for the premix that's being pumped through the engine. There is a **** of a storm of fuel/oil mix slinging around inside and getting on everything and everwhere inside. I'd hate to be inside and try to stay dry.
I've heard it is very hard to drill the rod some sort of very hard steel I don't know as I didn't try to drill one yet. But extra holes shouldn't hurt as long as you can deburr the hole on both ends. I'm not sure how a guy would deburr a torrington needle bearing housing on its inside there is the rub. Might be better to grind a opening and aline the opening with the rods holes before you press in that type of bearing into the rod.
Let us know how it goes.
 

sun

New Member
Apr 7, 2008
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Florida
Thanks for the replies! Norman, here is my roller bearing, I guess it is the caged type.


After posting my question I went ahead and *tried* to drill one hole at the top of the rod. What you heard is correct, it is very hard to drill and exceeded the limits of my bits, snapped four. Drilling was easy 95% of the way through and the last 5% is either hardened or hard-chrome plated or something. I never was able to get through it. After reading your post I think the risk of finishing/properly deburring the hole is higher than the risk of lube starvation. This was all prompted by a friend who I've been corresponding with- he just experienced engine failure and attributed it to the cage coming apart associated with over-rev and lube starvation due to no holes.

Thanks again
 

thatsdax

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Feb 22, 2008
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yes.. Holes should be drilled 120 degrees apart. 3 of them. this is typical with roller bearing uppers. one hole for solid. Solid or Roller bearings can be best. Depends on the metal and roller bearing used. The beauty of a Solid bearing is that when it starts to go, it gives warning. Rollers typically give no warning, and when they go, they take the whole top end, and even the bottom sometimes. Rollers do the most damage by far when they go. As for drilling, I can tell you, the connection rod is super super hard steel. I am not sure you will be able to find a bit hard enough to drill through it. I am sorry to tell you that news.. You should have at least one hole already. Thanks..
 

Pablo

Master Bike Builder & Forum Sponsor
Dec 28, 2007
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I think something was missed in China (imagine that) if you don't have one hole at least.

You should be able to drill it with a cobalt bit at reasonable speed and lots of coolant/lube. Finish with a diamond burr.

This is yet another reason even I don't recommend running these engines oil lean and I think a reason why most instructions say to use a synthetic oil.
 

sun

New Member
Apr 7, 2008
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Florida
I know of two boygofast 70cc motors that don't have any holes. I'm off to the tool store to search for uber-bits...
 

deacon

minor bike philosopher
Jan 15, 2008
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I have a boy go fast kit and have no idea if there is an oil hole or not. I really haven't heard much about them blowing but if it does, I'll be sure that everyone knows about it.
 

sun

New Member
Apr 7, 2008
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Florida
Well, a cobalt hard-metal bit didn't yield any new shavings from the hole. I ran it with coolant and low and medium speeds for quite a while. The cutters on the tip are showing signs of wear. It's frustrating because there is so little distance left to go. The upside is that the IDs of these connecting rods are HARD!!
 

Norman

LORD VADER Moderator
Staff member
Jan 16, 2008
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I think your right on a diamind bit they can be had a harbor freight in a set for around $30.00. I paid that for a set of diamond burrs a bunch of different sizes and shapes. I wonder if the rod is case hardened? A gun smith can tell you how to annel a small area to drill it if its hardeded at least I heard that from someone. I'm not up on it. I think you have to heat it up to a red color and stick it in lime dust or something you might look it up on the web or ask your friendly gun smith.
 

sun

New Member
Apr 7, 2008
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Florida
The diamond dremel bit did get a bit further into it, before the tip wore smooth. Two or so more might do the trick. $8+ is hard to swallow so I'll see what the local harbor freight has to offer tomorrow. That might be the answer: Chinese tools for Chinese parts!

I do have a go-to gunsmith, he might have some good bits...
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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A gun smith can tell you how to annel a small area to drill it if its hardeded at least I heard that from someone. I'm not up on it. I think you have to heat it up to a red color and stick it in lime dust or something you might look it up on the web or ask your friendly gun smith.

For drilling chromemoly or other tough (hardened) metals I always chucked up a hardwood dowel in the drillpress and ran it down on the spot to be drilled until it was smokin' good, then let it cool and drill.

Learned that from my Grandpa Elwood, 1901-1969.... real old school.
 

deacon

minor bike philosopher
Jan 15, 2008
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I like the drill with the wooden dowel idea have no idea if it would work but it just likes like my own dad sitting in his old half lit garage concocting some idea that looks like crap but works like a dream.
 

sisdavid

New Member
Mar 31, 2008
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Daytona Beach
Thatsdax, do you sell your engines with needle bearings? I bought one about 2 years ago, would it have needle bearings. I also bought one about a month ago a 70 cc, the one I bought about a month ago is scarry fast. The one with out the ecorn nuts, or maybe my old one has too many miles on it and I forgot what a new one was like. 2 years with hard rideing. like every day full blast up hills and everything.
 

thatsdax

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Feb 22, 2008
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the new ones are roller uppers. the past year or so. To be honest, I like the solid bearing as well. That is, if they use a hard metal for the solid. I also like the roller, that is, if they have a good cage and the piston and connection rod are proper for the roller. So.. Roller or Solid? Depends. Both can be best. I will use either in my engines. What ever is better. To be honest, I prefer the Solid if it is a good hard metal and does not wear out too fast. But Roller is what most people want for the upper. Not sure why. But roller upper is what is being sold currently. And they are working out well for sure. But I must say, if a roller goes, it takes out the whole top end and sometimes the bottom as well. The Solid gives warning when it starts to wear out and will not trash the motor like a roller can. But.. As long as the roller is a good setup, they seem to last and not cause any problems. In over a year now, I have only had 5 or 6 rollers returned for warranty. I must say, that is amazing. So..For now.. It is roller. Enjoy the ride..