Why to weld your XS650 Crank - For ALL engines

[Punkskalar]

http://hughshandbuilt.blogspot.com/2011/03/failed-cranks-why-to-properly-build-and.html

A bad crank can be cause for problematic charging systems, bearing wear, cylinder issues, and even be the answer for all those mystery aluminum shavings that keep coming up in your oil.

Ok, let me start off by saying that I have heard several people say that welding the cranks is a waste of time unless it is in a full race engine, big bore, etc.. Well I've been tearing down engines now for a few years, and have come across this more times than I can remember. This crank is just ONE example, but I've seen them come apart at the centers, rod pins, both, etc...


See how this rod pin isn't near flush with the flywheel?

Another view to give you an idea of the depth of the pin.

See this scoring on the flywheel? This is from the flywheel crashing into the cases. Not good folks.

To much side to side play in the rod = Uneven and non centered forces on the piston as the rod moves back and forth on the pin. This will cause pinching and binding in the cylinders as the piston travels up and down. Probably not a good thing.

Having a charging issue you can't solve? Might be directly linked to a crank coming apart as the flywheel has pushed the charging rotor into the alternator housing, grounding out and being a complete pain in the you know what to diagnose. I've had several engines come in with charging issues, only to find out that the entire system has been toasted due to the flywheels separating.


FYI - This was a stock bottom end, with a 750 Big Bore kit. I've seen this problem on many stock engines, big bore kitted engines, and non-welded rephased cranks as well. If you are putting money into your engine, make sure the crank is done PROPERLY.

So what is a Properly built crank you ask:

Simply put, it must be built from the center out. All pressed joints must be TIG welded for proper penetration and minimal buildup of filler material (clearances on the rod bearings and crank bearings are TIGHT around some of the welds). All clearances must be in spec, and all flywheels must be checked for runout before final welding. Yes, it takes time to do, but anything worth doing, is worth doing right the first time.

 

[CDNTX650]

Ask any Zuki GS owners or Kawasaki KZ owners what twisted cranks feel like after a missed shift.

 

[dgaf27]

is this something you can do for anybody else?

 

[Punkskalar]

is this something you can do for anybody else?

Do it just about weekly

Mostly doing it on the Rephased Cranks, the labor to do a stock crank would be identical, might as well go for the gusto if you are gonna do it

 

[spokes73]

I have read about crank problems over the years, and thought it was something that would never happen to me. Well, it did. My right side throw walked off center a little bit, threw a side load into the center crankshaft bearings tearing them up, and I had a bike that sounded like a threshing machine. I was steered to a Yamaha mechanic with years of experience, who knew exactly what my problem was when I put the crank on the counter. He has seen this a number of times.
In addition to fixing the crank he put a bead of weld on the crankshaft to prevent the throw from walking again. I asked him if the starter caused the problem, and he said no. He did say it could have been as simple as a backfire, or just bad juju. I have a bone stock 256, and I do not ride my bike hard, so I am still mystified as to how it happened. But it did.

I think this message is an excellent word to the wise. The pics are great and worth a thousand words. Thanks for taking the time to post the message.

 

[Classic]

So much for the old saying "XS650's have a bullet-proof bottom end".

When I get around to rebuilding mine I'll be sure to weld her up.

 

[Punkskalar]

So much for the old saying "XS650's have a bullet-proof bottom end".

When I get around to rebuilding mine I'll be sure to weld her up.

Make sure to weld the very center as well, not just the rod pins, but the #2 and #3 flywheels where they come together. I'll get a pic up of that this afternoon

 

[650Skull]

If you need to rebuild the crank is it possible to do after you have welded the pins, or is the crank a throw away

 

[Punkskalar]

If you need to rebuild the crank is it possible to do after you have welded the pins, or is the crank a throw away

If there is ever a need to rebuild the crank on these, you probably need to toss it anyhow

Seriously though, the only thing that will kill a welded crank is going to be lack of oil, or running super high rpms and spitting the rods out of the cases. I haven't been able to do that just yet, but I have been trying

The likely hood of the crank having issues AFTER being welded up is far less likely than a stock crank.

 

[Punkskalar]

Center pin welding. These are tricky to do, as the fitment is a bit awkward there for filler materials. The little bit of weld on the crank rod bearing surface will need to be cleaned away, and this was with TIG. MIG is nearly impossible to get the proper penetration and not build up too much filler in the process.


And some pretty colors on a rod pin after being welded

 

[hotdog]

Punkskalar,
After the final true up & welding of the outside of the rod pins on 1 & 4 flywheels, do you recheck the crank alignment..??
Just wondering if you have ever had one "pull" out of alignment from the welding process.

Cheers.

 

[gggGary]

A revisit on crank welding, I have one crank (stone stock 79 20K miles just run a bit hard) that I am sure is a throw away, and another (750 kit, big carbs, cam valves etc.)that just started making the dreaded bottom end "whir". I have "parked" both of those engines.
I'm a believer cranks should be welded if you have the bottom end apart or if you are going to run it hard.
I have a pile of "good" cranks to use, so no worries there for me.
I guess my question is how much welding is "enough"? do we need to go "full circle" or would a few (two? three?) beads spaced around the pins be enough or better even?
That weld that lapped up on to the thrust bearing surface is a bit worrying. I am leery of having to grind when there are open ball and roller bearings sitting there. I have thought that before assembly, a chamfer ground into pin and flywheel might help keep "bead build up" from being a problem.
Just running my thoughts by for anyone that wants to chime in. Has anyone talked to Mike Morse about this? Maybe he knows what was done "back in the day" and what modern flat trackers do about this? I know of a few ice racers and thought I might nose it around them too.
It wasn't mentioned in this thread but I'll assume the mildest possible filler rod should be used to reduce chances of stress cracking? Not much chance of pre or post heat being sane with the bearings being right there?
No answers, just questions.

 

[DIRTY DOG]

back when i raced atv's we used to weld the cranks in 3 spots around the pins,held ok
and it made it easier to rebuild (and cheeper didn't have to replace the crank's)
don't know about the xs650 eng. but that how I'm doing my 277 crank I'm building.

 

[gggGary]

Pictures Dirty Dog! Pictures when you do it!
Thanks for weighing in!

 

[DIRTY DOG]

ok when I get it done I'll post some pic's

 

[Punkskalar]

Center pin welding. These are tricky to do, as the fitment is a bit awkward there for filler materials. The little bit of weld on the crank rod bearing surface will need to be cleaned away, and this was with TIG. MIG is nearly impossible to get the proper penetration and not build up too much filler in the process.

And some pretty colors on a rod pin after being welded

*Now that I have been doing this for several years, without a SINGLE Crank failure in over 800 cranks or more - I have different processses. I don't want to confuse anyone, so I deleted the photo with the weld in the center of the flywheels. It was not up to our new processes standards.

 

[scabber]

gggGary Sounds like the 750 with the welded crank. Opinions differ on welding or the need on a non race bike. I would say crankshaft separating from rider abuse. I would say far I personally have seen 2. I have seen a lot more still doing fine. You have had a lot of these bikes how many. Put up a survey. I'm at the weld or not point. Or weld and see if you can beat it to death.

 

[Punkskalar]

A revisit on crank welding, I have one crank (stone stock 79 20K miles just run a bit hard) that I am sure is a throw away, and another (750 kit, big carbs, cam valves etc.)that just started making the dreaded bottom end "whir". I have "parked" both of those engines.
I'm a believer cranks should be welded if you have the bottom end apart or if you are going to run it hard.

Agreed

I have a pile of "good" cranks to use, so no worries there for me.
I guess my question is how much welding is "enough"? do we need to go "full circle" or would a few (two? three?) beads spaced around the pins be enough or better even?

We used to do full circle welding, with no failures to date, however we have updated our practice to 2 welds instead of one continuous. This should be standard practice, we learned as we went

That weld that lapped up on to the thrust bearing surface is a bit worrying.

Agreed, that was one of the first ever cranks that we built. We no longer weld in that area at all.

I am leery of having to grind when there are open ball and roller bearings sitting there.

There is NO way to keep grit and metal shavings out of those bearings, you MUST completely tear down the crank and do all prep before welding and build it accordingly. I have seen way to many damaged cranks/bearings because the time was not taken to remove the bearings before modification or "rebuild" of the crank

I have thought that before assembly, a chamfer ground into pin and flywheel might help keep "bead build up" from being a problem.

With MIG welding, that might be a problem for sure. We TIG weld all cranks, and buildup is extremely minimal if at all. On many of The OEM XS650 flywheels, there is already a chamfer in that location to fill

Just running my thoughts by for anyone that wants to chime in. Has anyone talked to Mike Morse about this? Maybe he knows what was done "back in the day" and what modern flat trackers do about this? I know of a few ice racers and thought I might nose it around them too.

It wasn't mentioned in this thread but I'll assume the mildest possible filler rod should be used to reduce chances of stress cracking? Not much chance of pre or post heat being sane with the bearings being right there?

I won't give away ALL my secrets but if you are putting enough heat into the rods or flywheels to distort them - you are using way to much heat to do the job. Again, NEVER weld near the bearings or with bearings installed. On the XS650 cranks, the outer flywheels are the last welded, so yes the rod bearings and rods will be in place, but again, heat control is KEY.

No answers, just questions.

These Cranks MUST be welded, about 20% of the cranks we see come in the door are seperating, and these were usually in stock engines. Add more CC's and Compression, and you are much more likely to have a crank failure.

I hope that helps - if you have any more questions, I'll be glad to help

Hugh
Hugh's HandBuilt

PS - If your crank doesnt look like this before reassembly, you are probably cutting corners...

 

[Punkskalar]

Punkskalar,
After the final true up & welding of the outside of the rod pins on 1 & 4 flywheels, do you recheck the crank alignment..??
Just wondering if you have ever had one "pull" out of alignment from the welding process.

Cheers.

Yes, when we first started rebuilding these cranks, we had a few pull from the welding. It was a nightmare to get them perfect AND welded. Now, we have been reworking cranks daily for the last few years - we've learned a thing or two We still check every single crank after welding, but the new processes we use do not cause any change in alignment or true at all.

 

[gggGary]

Great! Thank you so much Hugh! Yeah I've been shopping for a 50 ton press, didn't move fast enough, and missed a couple. I keep thinking a pair of wedges would aid in splitting.