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Some play in the left bearing is okay. I just went through this with my bike. If u want to replace it then replace it. You have to replace the crankshaft or the inner bearing race on the crank of you do.

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Some play in the left bearing is okay. I just went through this with my bike. If u want to replace it then replace it. You have to replace the crankshaft or the inner bearing race on the crank of you do.

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Hey man do you have something can send a video on?

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8 hours ago, 96motorhead said:

Some play in the left bearing is okay. I just went through this with my bike. If u want to replace it then replace it. You have to replace the crankshaft or the inner bearing race on the crank of you do.

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Uh...I hate to slam you like this, but none of that is true.

You dont want any detectable play in the left side crank bearing (up and down. Its a barrel type roller bearing). Run out (in and out play along the axis is common and not a problem as long as its not crazy excessive.

I have measured that left side inner race on every crank I have ever taken out, and Ive yet to find one that's been worn at all. What wears is the barrel bearing cage in the bearing that separates the bearings.

Also, that bearing race can be replaced. You can press the timing sprocket off the crank and replace it. HotRods offers that race in a main bearing kit. Huge plus. Here's the giant minus to the HotRods main bearing kit: The bearing cage in the left side is often made of plastic. I have one in the garage. The cage cracks, allowing the barrels to approach each other. The issue then becomes the non-round hole that the main bearing pin is running in. It allows the crank up and down movement and it makes a racket that is hideous. I just had an 09 engine that had a HR crank in it, with that cracked cage. I just put an OEM bearing on it, good to go.

If anyone wants the spec for that left side inner race, I have a brand new one I'll measure and post the size. As long as it's smooth and not lumpy, it's fine. Just change the bearing in the case.

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Uh...I hate to slam you like this, but none of that is true.
You dont want any detectable play in the left side crank bearing (up and down. Its a barrel type roller bearing). Run out (in and out play along the axis is common and not a problem as long as its not crazy excessive.
I have measured that left side inner race on every crank I have ever taken out, and Ive yet to find one that's been worn at all. What wears is the barrel bearing cage in the bearing that separates the bearings.
Also, that bearing race can be replaced. You can press the timing sprocket off the crank and replace it. HotRods offers that race in a main bearing kit. Huge plus. Here's the giant minus to the HotRods main bearing kit: The bearing cage in the left side is often made of plastic. I have one in the garage. The cage cracks, allowing the barrels to approach each other. The issue then becomes the non-round hole that the main bearing pin is running in. It allows the crank up and down movement and it makes a racket that is hideous. I just had an 09 engine that had a HR crank in it, with that cracked cage. I just put an OEM bearing on it, good to go.
If anyone wants the spec for that left side inner race, I have a brand new one I'll measure and post the size. As long as it's smooth and not lumpy, it's fine. Just change the bearing in the case.

Ok so don't use these bearings? I'll just save up the extra 30$ for oem

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2 hours ago, Shawn_Mc said:

Uh...I hate to slam you like this, but none of that is true.

You dont want any detectable play in the left side crank bearing (up and down. Its a barrel type roller bearing). Run out (in and out play along the axis is common and not a problem as long as its not crazy excessive.

I have measured that left side inner race on every crank I have ever taken out, and Ive yet to find one that's been worn at all. What wears is the barrel bearing cage in the bearing that separates the bearings.

Also, that bearing race can be replaced. You can press the timing sprocket off the crank and replace it. HotRods offers that race in a main bearing kit. Huge plus. Here's the giant minus to the HotRods main bearing kit: The bearing cage in the left side is often made of plastic. I have one in the garage. The cage cracks, allowing the barrels to approach each other. The issue then becomes the non-round hole that the main bearing pin is running in. It allows the crank up and down movement and it makes a racket that is hideous. I just had an 09 engine that had a HR crank in it, with that cracked cage. I just put an OEM bearing on it, good to go.

If anyone wants the spec for that left side inner race, I have a brand new one I'll measure and post the size. As long as it's smooth and not lumpy, it's fine. Just change the bearing in the case.

I can agree that its safe to say over a forum that no play is allowed, without being able to measure and feel it, it's a hard call.  From my research and experience as a mechanical engineering student, we should be seeing zero end play, no play in the right side bearing so it will have about .001" negative preload when heated up and .001" or so in the left side bearing in a theoretical situation.  Anymore play shows there is incorrect tolerance or wear between parts, usually the latter in this case.  The big question is how much wear is acceptable?  The answer to this question is different on a case to case basis.  My statement about some play being acceptable still stands, the amount depends on the circumstances and how it is measured.  For anybody wondering my bike had up and down play that measured at about .003" where the end of the woodruff key is in the crank and had .0001" (yes a tenth of a thousandth) of play measured on left crank half(the technical term has escaped my mind at this time) next to the rod.  I also brought my motor to a professional and it was declared that the play was fine in my situation.  I've been running it and will continue to run it with zero issues.  If you have any doubts by all means replace it, but to correctly do the job the inner left side race should be replaced if you do.

Edited by 96motorhead

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There's no preload, theoretical or otherwise on the crank pins. The crank pin slides into the right side crank pin bearing with minimal effort. The the crank literally floats in the middle of the two bearings. It can do this because the primary drive is a straight cut gear. If it was helical, it wouldn't work because the helix would pull the crank to or from depending on the angle of the helix (left or right) and worse yet, it'd go back and fourth because of acceleration/compression drive.

For what it's worth, even on a two stroke where you've got to press the cases together on the mains, you need to "center the crank" with a big ass whack of  a mallet to free any preload that ends up in the lower end. Some early Yamahas (70's two strokes) used to require the crank pins to be shimmed, as they actually did run a helical primary drive gear set up.

Acceptable oil clearances are typically .001" per 1 inch of journal diameter. This will maintain an oil wedge. But with roller bearings, you don't technically need an oil wedge. You need oil, but not as much as the friction isn't there except on the guides of the bearings (outside shells, or bearing cages) but those aren't work surfaces. Up and down play of .003" all the way out on the nose of the crank pin isn't much. Just setting up the tooling to be able to measure that very accurately makes me think this was a guesstimate by a "mechanic". I have dial indicators that measure to the tenth (.0001) and temperature alone begins to play a role in readings. 

I setup plain bearing engines oil clearances by hand. If you don't have a mic set, bore gauges and snap gauges (all Starrett mind you) you're dead. I've only been doing this shit for about 40 years though.

 

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