Crankshaft Rebuilding (NGC)

[Cdn850T5NT]

Folks, I just have to post this, as it is very instructive and interesting, if you are at all into 2 strokes.  The Kawasaki-produced manual on crankshaft rebuilding works for their singles up to their triples.  Very high skill levels and some equipment / jigs required to do this.

http://www.kawatriple.com/files/crankrebuild.pdf

[pete roper]

Rebuilding a pressed up crank for a single is an 'Acquired' skill. I used to be able to do it, don't know I'd like to try it again now! Multi throw cranks? Way above my pay grade!

One thing that will horrify many people unfamiliar with such things there is a LOT of smiting involved. Sometimes with substantial hammers!

Pete

[pressureangle]

Rebuilding a pressed up crank for a single is an 'Acquired' skill. I used to be able to do it, don't know I'd like to try it again now! Multi throw cranks? Way above my pay grade!

One thing that will horrify many people unfamiliar with such things there is a LOT of smiting involved. Sometimes with substantial hammers!

Pete

The first time I read a Harley-Davidson factory service manual, my mouth dropped open when I saw one of the required tools was a 5 pound lead hammer. By the time I got done fooling with H-D, I owned an 8 pound lead hammer. I never really became comfortable doing what was necessary.

[Mike Tashjian]

I did a few cranks way back and it becomes apparent very quickly that a lead hammer is the only way to do the final truing.  I still have a few lead and rawhide hammers of various weights in the back of the tool box.
You never know when you might need one.  Mike

[Cdn850T5NT]

The whole notion of a built-up crank, to me, sounds so so Mickey-Mouse.  And on a Harley?

Yeah, the forked conn rods on a Harley are neat (they allow the cylinders to be in-line, i.e. not offset, reducing vibration) but how can a friction fit crankpin be considered durable? I've seen said crankpins welded-in-place after crank alignment.  How can introducing welding heat to the crankpin NOT then subsequently affect crank TIR, "trueness"???

[oldbike54]

 The old Manx Norton manuals called for a 6 foot long cheater bar to *torque* the crankpin nut  Don't even get me started on the way HD designed their system , and the jig needed to properly align the flywheels 

 Dusty

[Cdn850T5NT]

Hey, I say it again: Guzzi bigblocks are "simple, stupid, durable". That's why I'm a fan!

[bigbikerrick]

Hey, I say it again: Guzzi bigblocks are "simple, stupid, durable". That's why I'm a fan!

I will take stupid and durable any day over , clever and fragile! Thats why I like the Guzzi "lumps" as well!
Rick.

[pressureangle]

Hey, I say it again: Guzzi bigblocks are "simple, stupid, durable". That's why I'm a fan!

Seen 'em all, rode on most.

And here I am. Don't see myself fooling with anything else unless it's historic or electric.

[Chuck in Indiana]

Seen 'em all, rode on most.

And here I am. Don't see myself fooling with anything else unless it's historic or electric.

This right there.. 

[Tusayan]

I did a few cranks way back and it becomes apparent very quickly that a lead hammer is the only way to do the final truing.

Having tried it both ways, on a single throw crank I found it a lot easier to work on a heavy surface table, hold the crank in both hands and lightly tap one throw on the surface to move it, using the inertia of the rest of the assembly. It works a lot better especially when you’re closing in on the last thou of run out.

[Cdn850T5NT]

That is useful info... it seems that it limits it to moving a small amount.  I imagine you tape the conn rod out of the way, so it does not hit the table.

You know, if the TIR can be changed with such relatively light (?) tapping, how in heaven's name can the built-up crankshaft survive the explosions... AKA as cylinder firings without losing the correct TIR and other crankshaft alignment parameters?  That is the amazing thing to me.  But I guess the heavy-metal balancing slugs help matters, and maybe the two-stroke cylinder firings are weaker than a four-stroke's.

Do folks know whether any four-strokes use built-up cranks, as well?

[pete roper]

That is useful info... it seems that it limits it to moving a small amount.  I imagine you tape the conn rod out of the way, so it does not hit the table.

You know, if the TIR can be changed with such relatively light (?) tapping, how in heaven's name can the built-up crankshaft survive the explosions... AKA as cylinder firings without losing the correct TIR and other crankshaft alignment parameters?  That is the amazing thing to me.  But I guess the heavy-metal balancing slugs help matters, and maybe the two-stroke cylinder firings are weaker than a four-stroke's.

Do folks know whether any four-strokes use built-up cranks, as well?

Yup, lots of them. The last ones I did were Honda singles in the early 1990's but I'd imagine a lot of them still do. All the big Zook and Kawa fours back then had pressed up cranks with roller mains and big ends too.

Pete

[1down5up]

Do folks know whether any four-strokes use built-up cranks, as well?

Just about every English bike (Norton, Triumph), bevel ducati (at least the earlier ones, not sure about the darmahs etc), even the 250cc 6 cyl Honda race bike, and that's alot of crank pins etc to get just right.

[Tusayan]

The very last bevel Ducatis built in 1984/85 had a one piece crankshaft.  Typically that means electric start 900 and Mille Hailwoods. All those before were pressed together.

[n3303j]

Do folks know whether any four-strokes use built-up cranks, as well?

The whole BMW /2 series used a multiple part crankshaft.
The Ural still uses a multiple part crankshaft.
BMW had little problem with the design on their kick start bikes.
Ural had a number of problems when operators would use electrical start on a partially hydrolocked cylinder. The heavy flywheel had enough inertia to twist the crank parts out of alignment.

[Rough Edge racing]

Just about every English bike (Norton, Triumph), bevel ducati (at least the earlier ones, not sure about the darmahs etc), even the 250cc 6 cyl Honda race bike, and that's alot of crank pins etc to get just right.

 Not exactly,Brit 360 degree  twins, like just about or all of them. had one piece cranks... Some of the 70's japanese 4 cylinder engines have built up cranks..

[huub]

actually having a pressed up crank has its advantages, it is easy to change a crankpin.
on a guzzi smallblock you have to scrap the crank if worn or damaged
usually the engine gets scrapped , a used engine is cheaper than a new crank.

[Rough Edge racing]

actually having a pressed up crank has its advantages, it is easy to change a crankpin.
on a guzzi smallblock you have to scrap the crank if worn or damaged
usually the engine gets scrapped , a used engine is cheaper than a new crank.

 Various welding techniques can and are used to repair a damaged crank when no undersize bearings are available...

[huub]

unfortunately the added metal is ok to run a bearing on, but has no strength ,
ok for industrial diesels, but not recommended for high performance engines ( i tried) 

[Rough Edge racing]

unfortunately the added metal is ok to run a bearing on, but has no strength ,
ok for industrial diesels, but not recommended for high performance engines ( i tried) 

 This guy has had a few welded for performance V8 car engines. Is this the procedure you had done?

         

Yes they will survive just fine. I have run them back in performance applications after that type of repair with no dramas,the better weld method is submerged arc weld which is a far better repair than spray welded journals imo. I dont know what the cost is over there but you need to weigh that up to see if its a vialbe option and a crank worth saving not a cheap scat deal.

[huub]

i had cranks spray welded and cranks hard chromed,  works fine , but they have to shave some metal from the bigend before the process , to achieve a even layer.
so if the crank was already highly stressed you are taking a risk.
Guzzi does not provide oversize shells, and does not advice repairing crankshafts, not sure what that means.

[Rough Edge racing]

i had cranks spray welded and cranks hard chromed,  works fine , but they have to shave some metal from the bigend before the process , to achieve a even layer.
so if the crank was already highly stressed you are taking a risk.
Guzzi does not provide oversize shells, and does not advice repairing crankshafts, not sure what that means.

 I had my vintage Triumph race bike crank spray welded, but it's for the roller main bearing press fit...I suppose it all boils down to cost...Proper crank welding on one journal and machine work might be $200 and then having the crank nitrided to relive stress.Some shops recomend a cyro process..
 The cranks in my race Triumphs are 60 years with an unkown history...heat treating like nitriding ,carburizing or cryo is  to relive stresses and improve fatique resistence...I have no idea if Guzzi heat treats their forged cranks,but probably..