Connecting rod free play

[n4mwd]

So I ordered a used short block for the 250 and I noticed that when I twist the rod perpendicular to the crank (like a screwdriver) there is a noticeable slop or free play in the bearing. Video below. I was wondering if this is acceptable for a journal that is only about half an inch wide or if this is too much. There is no detectable up and down free play (the way the piston moves).

Anybody have any experience with rod bearings that can answer this?

Link to original page on YouTube.

[Racer x]

That is no good. The clearance is thousands of an mm . That looks like the motor has a lot of sludge also.. How much did you pay? The head is worth good money if the cams are ok

[choneofakind]

Yeah the head is worth money!! Especially when you run into people like me who unexpectedly found stripped plug threads
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[n4mwd]

Originally Posted by Racer x

That is no good. The clearance is thousands of an mm . That looks like the motor has a lot of sludge also.. How much did you pay? The head is worth good money if the cams are ok

I only got the short block. No head. Paid $200 more than its apparently worth.

I'm going to call the ebay seller and ask what's next.

[alex.s]

yeah the seller ripped you off sorry bro. i would file a paypal complaint if he doesnt refund you. paypal is great about giving you back your money but you have to do it fairly quickly i hear

[n4mwd]

I called the ebay dealer and told him what you said and I suspected. I told him that I was willing to split the case and inspect the crank. Basically, he's willing to refund the full purchase price if the crank or rods are bad - and the cost of new bearings if its only the bearings.

[Racer x]

You should try to fix it if you can. The last rocker arm 250 ninja engine was 2007 that is six years ago. In four years you will not find any used engines.

[alex.s]

if the bearings have gone already wont there be lots of damage to both the crank journal and the rod surfaces? seems expensive to fix

[Motofool]

Originally Posted by n4mwd

I called the ebay dealer and told him what you said and I suspected. I told him that I was willing to split the case and inspect the crank. Basically, he's willing to refund the full purchase price if the crank or rods are bad - and the cost of new bearings if its only the bearings.

Appreciable rotation means the bearing is not cylindrical anymore; therefore, enough oil pressure can't develop.
Connecting rod twist service limit is 0.2 mm at the end of a 100 mm lever.

Actually, you could measure the actual clearance by moving the rod up and down against a dial and compare it to limit spec (0.10 mm).

It is not easy to precisely measure it after dissembling it:

http://www.carcraft.com/techarticles...e/viewall.html

[alex.s]

@Motofool dont they make little ink strips that you can put in and fully assemble then disassemble and measure the crush thickness? i forget what they are called... maybe thats too big of a clearance for those.

[davenay67]

Originally Posted by alex.s

@Motofool dont they make little ink strips that you can put in and fully assemble then disassemble and measure the crush thickness? i forget what they are called... maybe thats too big of a clearance for those.

Plastigauge

[n4mwd]

That's a good idea. I actually have some of those and was wondering how I was going to test this thing.

I got it apart, removed one rod, and can't find anything wrong with it. They twisted and wobbled as shown in the video, but the caliper says they are all OK and there is no signs of wear on either the bearing or the crank.

I didn't take the other one off yet until I figure it out. I'm going to use some plastigage to check to see if the clamp pressure is even. If it is, I'm probably going to just throw it all back together and start riding.

I'm thinking I might take the crank to a bike mechanic and ask him what he thinks.

[n4mwd]

The plastigage shows the bearings are in the tight end of the spec. It showed a clearance of 0.038mm and the acceptable range is 0.031-0.059 with a service limit of 0.10mm.

SO the plan is to ask the mechanic. Could be something I'm overlooking.

[Racer x]

Take the crank and rods to a machinest. A bike mechanic will not have the tools for that.
In the video it looks like a lot more play than you describe. Measure the crank see if the machinest can polish the crank and re fit with new bearings. You also need to replace the rod bolts.

[n4mwd]

The bike mechanic said the bearings were burnt. He said they have been rubbing the rods the wrong way and got burned. The crank looks good, but I'm not certain about the rods. The rod looks scuffed under the bearing. He said I should get all new rod bearings. I also need to get new bolts, but they said I could use the same nuts.

[Racer x]

The bolts come with nuts. Let me see some photos of the crank rod ends and bearings. Don't mix up the rod caps.

[n4mwd]

Originally Posted by Racer x

The bolts come with nuts. Let me see some photos of the crank rod ends and bearings. Don't mix up the rod caps.

Sorry about that. I've attached one here. It opens up to higher res for more detail.

Upon examination, it appears that the rods are out of round by about 3-4 thousandths of an inch. The crank journals appear round. Unless there is a way to fix these rods, I'm thinking I need new ones.

[Racer x]

The bearing look spun to me but I a m looking with a phone. You need a machinest to see if he can turn the crank and tru the rods and te balance shaft. This will fix but it will not be cheap.

[choneofakind]

N4mwd, what happened to your engine that you have it in pieces like this? I would offer you parts, but I don't exactly have any spare engines laying around...
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[n4mwd]

Originally Posted by Racer x

The bearing look spun to me but I a m looking with a phone. You need a machinest to see if he can turn the crank and tru the rods and te balance shaft. This will fix but it will not be cheap.

They do have a spun appearance, but the crank is fine, no scratches, true and perfectly round. I am suspecting that had the donor bike not been totalled by the insurance company, the bearings would have eventually damaged the crank. So it looks like we got it just in the nick of time.

I talked to a machine shop guy and they said they could fix the rods by shaving the cap mating surfaces and then re-boring them to bring them back to factory spec. The guy who sold me the short block said he would pay for it.

Originally Posted by choneofakind

N4mwd, what happened to your engine that you have it in pieces like this? I would offer you parts, but I don't exactly have any spare engines laying around...
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Its not my regular bike, its for a rescue bike. Specifically, a 2007. However, the guy I bought it from seriously misled me and it turns out the engine was blown with a mangled crank. The parts I'm talking about here are to a short block that I bought separately for the rescue bike, but it turns out there is a problem with the bearings on that too. So I had to split the case and examine the crank, rods and bearings to figure out what is wrong with it.

Its still not right, but I'm getting closer.

[n4mwd]

Originally Posted by Racer x

The bolts come with nuts.

Where do you get your bolts from? The dealer sells the nuts separately. Bolt = $5.68, nut = $3.34. I'd prefer to change both. Is there an aftermarket equivalent?

I stretched one of the old bolts trying to torque it down. I'm thinking they must be made of some pretty sorry steel to stretch like that. I think even aluminum would do better.

[LoD575]

Originally Posted by n4mwd

They do have a spun appearance, but the crank is fine, no scratches, true and perfectly round.
I talked to a machine shop guy and they said they could fix the rods by shaving the cap mating surfaces and then re-boring them to bring them back to factory spec.

Originally Posted by n4mwd

I stretched one of the old bolts trying to torque it down. I'm thinking they must be made of some pretty sorry steel to stretch like that.

Spun rod bearing is what it looks like to me. With that type of spun bearing the crank is normally in good shape.
Good sign the machinist knows what he is doing.

The cap bolts are only intended for single use. They are designed to stretch with proper amount of torque applied.

Cylinder head bolts are a common application for stretch upon torque single use only bolts.

[Racer x]

Originally Posted by n4mwd

Where do you get your bolts from? The dealer sells the nuts separately. Bolt = $5.68, nut = $3.34. I'd prefer to change both. Is there an aftermarket equivalent?

I stretched one of the old bolts trying to torque it down. I'm thinking they must be made of some pretty sorry steel to stretch like that. I think even aluminum would do better.

I get my parts from Cheap Cycle parts.com. OEM and good price. Shipping is quick.

[jasle]

Originally Posted by LoD575

Spun rod bearing is what it looks like to me. With that type of spun bearing the crank is normally in good shape.
Good sign the machinist knows what he is doing.

The cap bolts are only intended for single use. They are designed to stretch with proper amount of torque applied.

Cylinder head bolts are a common application for stretch upon torque single use only bolts.

They are called torque to yield. you torque them until they start to stretch. typically you can measure them and see if they can be reused on cars. sometimes you get a second use out of them...but for the cost not worth it in this case.

I have seen several insurance bikes that had roasted cam journals due to oil starvation whilst running on its side. With how nasty that bottom end looks I would suspect the PO just never changed the oil.

[n4mwd]

Originally Posted by jasle

They are called torque to yield. you torque them until they start to stretch. typically you can measure them and see if they can be reused on cars. sometimes you get a second use out of them...but for the cost not worth it in this case.

I have seen several insurance bikes that had roasted cam journals due to oil starvation whilst running on its side. With how nasty that bottom end looks I would suspect the PO just never changed the oil.

I took the crank, bearings and rods to the dealer and had him look at it. He said that the bearings were not spun after all. He went and got a ZX-10R rod and showed it to me and said that kawi rods all look like that. Seems strange, but that's what he said.

Running on side... +1 I have to admit, that is the answer I've been looking for. I think both this short block and the rescue bike were involved in accidents. Running on their sides would explain why the oil pump lost prime and let the bearings run dry. Both bikes allegedly had low miles (5K-6K).

Anyhow, its a much more palatable explanation for the loss of oil pressure than assuming that the PO let it run without oil (ignoring the fact that a bike with only 5K miles would not likely be out of oil in the first place). Thanks, its starting to make sense.