RZ350 Crank Inspection

General forum on engines, transmissions, gearing and modifications to each

Moderator: rztom

Post Reply
Message
Author
User avatar
kobra
Posts: 798
Joined: Sun Sep 16, 2018 12:53 am
Location: Bay Area CA

RZ350 Crank Inspection

#1 Post by kobra » Sat Dec 22, 2018 3:14 am

Hi guys, feeling bored? Want to watch me have an OCD tweak-fest and do a used crank inspection?

I have decided to buy a new OEM crank since it's the heart of the motor and I'm doing a full resto. However... I am very interested in learning about how this stuff works in the process. So I went through an inspection on my current crank and documented it in the video. It got me thinking, what is the failure mode for a 2 stroke crank? Do the clearances stay steady and then it suddenly fatigues and fails, or is the wear pretty linear? Based on my numbers, can I calculate the remaining life left in this crankshaft or is it impossible to tell?

Thanks for your input, and please excuse my slow talking. I was trying to video and articulate my words at the same time.


MK
Posts: 814
Joined: Sat Nov 26, 2005 11:44 am
Location: Wolfenbüttel, Germany
Contact:

Re: RZ350 Crank Inspection

#2 Post by MK » Sat Dec 22, 2018 8:08 am

The grooves on the stator side are a little above normal. Especially the one close to the bearing.
If you plan a race use or only a few years on the road, it'll be just fine.
If you're the guy building for eternity, then this needs to be fixed.

You mentioned the bearings "wiggle". That's normal for crank bearings as they have bigger tolerances than let's say a wheel bearing.
If I remember right it's a C3 on the RZ but I've seen C4 and C5 on other bikes cranks.
https://www.machinedesign.com/mechanica ... -clearance

Last but not least you forgot to measure the most important point: The runout.
Usual setup is supporting the inner bearings and measure the outside while slightly turning the crank.
But I've also seen people supporting the outside bearings (or putting it in a lathe like you) and measuring the inner ones.
The tolerance is 5/100 mm, but usually you find even bigger values in aftermarket stuff after shipping. There are people who claim 0-2/100 mm would be the value to target.
Bye
Martin

brrrappp
Posts: 603
Joined: Tue Sep 18, 2018 10:21 pm
Location: USA

Re: RZ350 Crank Inspection

#3 Post by brrrappp » Sat Dec 22, 2018 10:03 am

kobra wrote: Sat Dec 22, 2018 3:14 am It got me thinking, what is the failure mode for a 2 stroke crank? Do the clearances stay steady and then it suddenly fatigues and fails, or is the wear pretty linear?

The below observation of vampires by Edgar Frog is applicable to crank failures as well.

I think I should warn you all, when a vampire bites it, it's never a pretty sight. No two blood suckers go out the same way. Some yell and scream, some go quietly, some explode, some implode. But, all will try and take you with them.



If you do regular tear-downs you may catch an imminent failure by measurement.
My experience with crank failure has been foreign substance contaminating the engine. Water, dirt, broken piston causing lower rod bearing to be damaged/worn/pitted. Having worked at Motorcycle and snowmobile dealerships I saw the results of major failures more than I saw replacement due to wear.
Last edited by brrrappp on Sat Dec 22, 2018 11:11 am, edited 2 times in total.

User avatar
kpke
-----
-----
Posts: 2531
Joined: Sun Nov 23, 2008 2:22 pm
Location: Livermore, CA

Re: RZ350 Crank Inspection

#4 Post by kpke » Sat Dec 22, 2018 10:27 am

Very nice video. Thanks for posting that.

I am curious if you will do the same inspection on the brand new OEM crank and compare results???

User avatar
Smoker
Posts: 4778
Joined: Sun Mar 23, 2008 8:08 pm

Re: RZ350 Crank Inspection

#5 Post by Smoker » Sat Dec 22, 2018 2:11 pm

Enjoyed the video very much!

Good camera work and commentary.

Looking forward to more.

User avatar
kobra
Posts: 798
Joined: Sun Sep 16, 2018 12:53 am
Location: Bay Area CA

Re: RZ350 Crank Inspection

#6 Post by kobra » Sat Dec 22, 2018 10:39 pm

MK wrote: Sat Dec 22, 2018 8:08 am The grooves on the stator side are a little above normal. Especially the one close to the bearing.
If you plan a race use or only a few years on the road, it'll be just fine.
If you're the guy building for eternity, then this needs to be fixed.

You mentioned the bearings "wiggle". That's normal for crank bearings as they have bigger tolerances than let's say a wheel bearing.
If I remember right it's a C3 on the RZ but I've seen C4 and C5 on other bikes cranks.
https://www.machinedesign.com/mechanica ... -clearance

Last but not least you forgot to measure the most important point: The runout.
Usual setup is supporting the inner bearings and measure the outside while slightly turning the crank.
But I've also seen people supporting the outside bearings (or putting it in a lathe like you) and measuring the inner ones.
The tolerance is 5/100 mm, but usually you find even bigger values in aftermarket stuff after shipping. There are people who claim 0-2/100 mm would be the value to target.
You're right - I didn't measure the runout! I will have to do that still... All the procedures I've seen do this without bearings installed and the crank mounted on V-blocks, but I guess I can just spin it on the bearings. Will report back.

Regarding the grooves on the crank seal area, I checked the primary drive gear and it also has a similar pattern. The inner lip has a deep groove (deep being like .002") and outer is just polished looking. Think I need to replace that too or does it make a difference?
Last edited by kobra on Sat Dec 22, 2018 10:48 pm, edited 1 time in total.

User avatar
kobra
Posts: 798
Joined: Sun Sep 16, 2018 12:53 am
Location: Bay Area CA

Re: RZ350 Crank Inspection

#7 Post by kobra » Sat Dec 22, 2018 10:39 pm

kpke wrote: Sat Dec 22, 2018 10:27 am Very nice video. Thanks for posting that.

I am curious if you will do the same inspection on the brand new OEM crank and compare results???
Yes that's the plan.

Post Reply