Glue the main bearings?

[tschisi]

Hi!

I?m in the middle of my bottom end rebuild, but now i?m facing a big problem.

My crank was worn.
A well-known honda machine shop which owns a race team itself, repaired it.
I?ve already got the seals and bearings in the cases, and the crank in the right case.
Now i noticed that i can slide the left main bearing, which is not installed yet, onto the crank and remove it again!
 


I called the shop and they told me that in some engines the crank is designed in a way that one crank-side is "thinner" for assembling and dismanteling reasons.
I never heard of something like that in k5 engines. 

They sent me some kind of loctite (in fact it?s Honda Lock 3, a threadlock from honda) to glue the bearing onto the crank while putting the left case on it (and hope that enough of the glue stays between shaft and bearing instead of getting wiped onto the seal).
It?s supposed to last 100hrs, which wouldn?t be shorter than the mains or conrod i think.

What do you think?

[NZ500]

Hi. It's a worry that they'd recommend doing that. It's not good/reliable. There's probably new cranks available for a reasonable price in America. Mrcycles seems to do an alright deal on OEM parts if you're not keen on a cheaper hotrods kit.

I'm in New Zealand and have recently had both sides of my crank ground down, hard chrome plated and then ground to factory spec again. The surface is very hard then and should last forever. Have had it done on other bikes and it worked well.

Unless you've got high compression or crank is out of balance/align I would expect the bottom end to last a lot more than 100 hours if done right.

[jonny500]

yes that is correct 1 side of the crank is a micron of so less, that is why when you split the cases 1 bearing almost always stays on the crank and 1 in the case. if you crank is worn on the journal you have a problem and it needs sorting properly. imo there is no glue known to man that could with stand the abuse a k5 crank gets and i would not be using it. just my opinion anyway. p.s the main bearings should go in the casing first not on the crank

[kwakman]

IMO, both the above replies are on the money.which saved me a sh&tload of typing.Nice

[tschisi]

1 side of the crank is a micron of so less

But not so much that i can slide the bearing just onto it, right?

if you crank is worn on the journal you have a problem

It was worn, that?s why i sent it to the "machine shop"

the main bearings should go in the casing first not on the crank

That?s what i wanted to do, i just tried to slide the bearing on casually.

[Polar-Bus]

Hi!

I?m in the middle of my bottom end rebuild, but now i?m facing a big problem.

My crank was worn.
A well-known honda machine shop which owns a race team itself, repaired it.
I?ve already got the seals and bearings in the cases, and the crank in the right case.
Now i noticed that i can slide the left main bearing, which is not installed yet, onto the crank and remove it again!
 


I called the shop and they told me that in some engines the crank is designed in a way that one crank-side is "thinner" for assembling and dismanteling reasons.
I never heard of something like that in k5 engines. 

They sent me some kind of loctite (in fact it?s Honda Lock 3, a threadlock from honda) to glue the bearing onto the crank while putting the left case on it (and hope that enough of the glue stays between shaft and bearing instead of getting wiped onto the seal).
It?s supposed to last 100hrs, which wouldn?t be shorter than the mains or conrod i think.

What do you think?

your engine builders comments are correct. Many race shops emery sand the crank stubs to allow a precise "slip fit" between the crank and bearings. OEM is always a press fit. My 12,500 rpm  Honda CR125 shifter kart engine has been modified for "slip fit" removable bearings. Slip fit bearings makes for an easy, trouble free dissasembly. The engine builder probably noticed some wear on the crank bearing surfaces, then just machined them to the "slip fit " dimensions. You won't have any negitive effects running a slip fit crank.

[dave916]

I personally would not fit a slip fit bearing in a kx500, i think there is too much side clearance on the kx crank  , it will damage the seals  , the vibration of a 500 crank #[far more than a 125]will also make a slip fit a looser fit afer a while

as for the honda [cr500] you may get away with slip fit due to a tighter side play
and the main bearing on clutch side is locked to the crank by primary gear and seal sleeve

 

[kwakman]

its the left journal that is slightly smaller.with the right side having the primary/clutch relationship to give something to stop this side of the crank deflecting, it would make sense to me to have them hard chromed when worn, and do them both to the right side spec. if you would rather have one looser for ease of disassembly, have the right looser and the left tight as having flywheel mass and nothing to assist against deflection means the left side bearing (therefore seal too) has to work harder, without the benefit of an oil bath in case of the seal. when I pulled mine (previous owner could pick his toenails without bending down) (thats a neanderthal themed funny, laugh or I'll club ya!) the first thing I noticed when I pulled the crank was the left side bearing had WAY more play than the right.I think the above is the reason.K.

[kwakman]

some guys also use a spot of blue loctite on the journal/bearing face, but usually when having normal tolerances, not to fix an issue. it may be akin to taking aspirin as a cure for decapitation. not heard of the slip fit method before so cant comment on its reliability, but when I think of the mass of the K5 crank at full tilt I'd rather use the hard chrome route. I know your build has been a steep learning curve, and like many of us around the globe, money isn't easy to come by.Play safe and hard chrome is my advice.K.

[Motorrad]

In my motor build thread,.. It lists the loctite you need to fix your problem.

[jonny500]

slip fit hmm i would like to know the result of this experiment. unfortunatly my 500 motor is built now so i cant try it in mine, what a shame i found some pics dont mean to worry any one

[kwakman]

Uh hmm. thats what I'm talking about.K.

[Motorrad]

slip fit hmm i would like to know the result of this experiment. unfortunatly my 500 motor is built now so i cant try it in mine, what a shame i found some pics dont mean to worry any one

That motor didnt fail due to a slip fit bearing....     Or any kind of main bearing issue   from what I see in those pictures...     


My Personal vote.... Cast piston strikes again

[jonny500]

slip fit hmm i would like to know the result of this experiment. unfortunatly my 500 motor is built now so i cant try it in mine, what a shame i found some pics dont mean to worry any one

That motor didnt fail due to a slip fit bearing....     Or any kind of main bearing issue   from what I see in those pictures...     


My Personal vote.... Cast piston strikes again

i know, just making a point. there are some big pieces of metal moving very fast in there and when things go wrong it can get messy and expensive. motorad, did you use a slip assembly on your motor, i have never heard of it but must say i am a skeptic

[jonny500]

1 side of the crank is a micron of so less

But not so much that i can slide the bearing just onto it, right?

correct

if you crank is worn on the journal you have a problem

It was worn, that?s why i sent it to the "machine shop"

why did they not fix it

the main bearings should go in the casing first not on the crank

That?s what i wanted to do, i just tried to slide the bearing on casually.

sorry i miss understood