Topic: My old 1124 sohc drag bike motor, final report. Post Mortem.

[Don R]

  I have the dragbike up on the shelf, the engine has a welded stroker, I forget the bore/stroke it's written somewhere. The engine appears to be intact but I've been advised to not run the old welded crank even though it mags as good as a welded crank can.
 I'd like to run the bike down the track, We run a dragster and are there anyway so why not? What's the thinking on this motor? Go stock crank, 900 crank or just run it as is and hope for the best? I have most of an F2 motor and an F2 freshly  backcut trans. I could slap an 811 K3 cylinder on the F2 cases and use the good K1 head.
 I'm not opposed to an auto, we already race with a 2 speed. might be more my style.
 I'm not sure about rod length and piston pin height but I'd expect them to not work at all with a stock stroke.
 
 

[dragracer]

So why does your source advise against running a welded and stroked crank. They do the same thing these days' on the newer engines to increase the stroke. As long as you have proper bearing clearances on the rods and mains, why not use what you have now. In my experience, most striker crank failure has been due to improper bottom end maintenance. You simply cannot beat up on the motor without splitting the cases periodically to replace the rod and main bearings. Its just the sacrifice you make to get the extra cc's. Heck, if you don't want to run the crank, I'll trade you for the crank and the rods for a 900 crank and rods.  As long as your crank checks out alright now, I've got just that much confidence that it will be fine for you to use. 

[Jerry Rxman Griffin aka MuthaF'er]

Don,

RUSM?    Sounds like it's ready to go. See you in Valdosta next month ridin that #$%*!

[dragracer]

Don, you need to go after the ET and mph bonus money with that big motor.

[Don R]

 True, My bike guy said it's a matter of when the crank will break not if.
 He's a multi time NHRA bracket bike champ, going to Pomona again this year. They move around to different tracks to avoid dominating the same track every year. l0l.

[NitroHunter]

Don, unless you are planning to strap on a blower and fill 'er with strait pop, I'd trust this crank. As you know 'Stroked Torque Monster' is a relative term.
The mag doesn't lie. 

[bear]

I never got much more than twenty hours out of a welded SOHC crank.
Some times not even that.

I do know that bearing wear was not an issue, other than damage caused by the cranks themselves.

But then again, I didn't have access to APE units and the like.

Cheers,
Brian

[MRieck]

I never got much more than twenty hours out of a welded SOHC crank.
Some times not even that.

But then again, I didn't have access to APE units and the like.

Cheers,
Brian

They all break. I am sure Jay would agree that a billet unit is the real solution.

[scottly]

I never got much more than twenty hours out of a welded SOHC crank.

Twenty hours is a long time on a drag-strip.

[bear]

I never got much more than twenty hours out of a welded SOHC crank.

Twenty hours is a long time on a drag-strip.

I suppose it is Scott.
But it equates to less than half a race season for us.
Not that would have been a major issue either but it wasn't a service interval issue.
I've had them fail straight up and I've had them run up to the twenty hour mark.
Half of the failures where catastrophic.

Cheers,
Brian

[Retro Rocket]

I never got much more than twenty hours out of a welded SOHC crank.

Twenty hours is a long time on a drag-strip.

I suppose it is Scott.
But it equates to less than half a race season for us.
Not that would have been a major issue either but it wasn't a service interval issue.
I've had them fail straight up and I've had them run up to the twenty hour mark.
Half of the failures where catastrophic.

Cheers,
Brian

In a chair I imagine that would be quite scary....

[bear]

In a chair I imagine that would be quite scary....

I'll let you in on a little secret..................that thing used to scare the siht out of me just idling in the work shop.
Get Lindsay to take you for a run sometime and let me know if you could still feel your balls after.
Mine where usually up somewhere around my Adams apple.

Cheers,
Brian   

[Retro Rocket]

In a chair I imagine that would be quite scary....

I'll let you in on a little secret..................that thing used to scare the siht out of me just idling in the work shop.
Get Lindsay to take you for a run sometime and let me know if you could still feel your balls after.
Mine where usually up somewhere around my Adams apple.

Cheers,
Brian

 

[Don R]

;')

[NitroHunter]

Long ago when I was a regular customer, I tried to get SoCal crank grinder Henry Velasco to build me some billet stroker SOHC cranks from his Velascoloy materiel, he just grinned and told me they'd cost as much as our funnycar cranks by the time he was done. Gulp.    And really, he just wasn't interested in making anymore bike cranks.
Then he showed me several billet V45 units he built (I think for American Honda, not positive) those things were really nice looking pieces, but that project had ended and he had barely broken even on the R & D.
Welding is the preferred journal repair method vs chroming, and in a low lifecycle unit (billet race crank) I can't actually say I've seen Death Cracks appear more often in a weld repair unit than not. But again this is an extreme horse power, VERY low lifecycle application. Counting warm ups, burnouts and staging, and runs, they may see an hour of use during it's service life. And WAY less than a minute under load. And inspected every couple minutes of running. Probably not what you had in mind Don. 
Sorry, got to rambling there...
Anyone know what the life of those RC welded stroker kits was on the street?

[Bill/BentON Racing]

I sure would like to know!! Bill

[teebee67]

Me too, I have a motor fitted with a stroked RC crank and big bore kit.

[dragracer]

Does Jay still offer stokers service on the sohc cranks??

[Jerry Rxman Griffin aka MuthaF'er]

Do believe so.

[NitroHunter]

Me too, I have a motor fitted with a stroked RC crank and big bore kit.

Hey Tee, sounds great, what kind of mileage do you have on it?
Long ago Dave Dodge told me of a RC stroker big-bore bike that was having the wheels rolled off it as a two-up touring machine, it sounded like many thousands of highway miles. This was back around the time of their 30k mile Kawi big bore kit adds.
Not a race application but telling none the less. Not sure I see the issue with such a minor amount of journal weld-up when used in less than extreme applications.

[teebee67]

Don't know the mileage as the motor came as part of a project but it all looks good inside so I am going to chance it in my spare race bike. If it turns out well I might put it in my number 1 bike.

[Don R]

 I decided to run it if I can get it back in shape. It had some chewed up o rings in the pump screen but the rest of it looked OK to my untrained eye.

The motor was tight after re-assembly and checking, It had a spot where it would turn easier and then get tight. I removed parts one at a time checking and it was relieved only when loosening the main bearing case bolts. I worried that I had gotten case sealer in the bearings or a shell was in wrong.
 So far I've only lifted the bottom half enough to see the bearings, they appear shiny, I polished them with white scotchbrite while it was apart. I did have assembly lube on them so still don't have an answer. The trans wants to lift out with the case so I still have parts to remove. The kick starter was too tight to use before and I replaced all the kicker parts with no result. The oil pump looks good too.
 When I bought it, I could rock it in gear and the motor turned but wouldn't kick over.
 The PO is deceased and I don't know the condition he left it in or the last time it ran. I'm close to taking it to a drag bike shop and turn them loose on it.

[kmb69]

.....
The motor was tight after re-assembly and checking, It had a spot where it would turn easier and then get tight. I removed parts one at a time checking and it was relieved only when loosening the main bearing case bolts. I worried that I had gotten case sealer in the bearings or a shell was in wrong.
.....

Be willing to bet money you will find that welded, stroker crank is running out.
That was the typical problem with the welded cranks from back in the day and it usually did not end well over the long, (sometimes short) haul.
The metallurgy in the crank has been "upset" and it was probably not re-heat treated before grinding and it is bending, with possible permanent deformation, under load.
They also usually only reground the rod journals instead of building up all the journals, re-heat treating, then grinding all of them.
Welding technology has come a long way over the last 35-40 years but most of these old welded strokers out there come from that era.
They are able to build up cranks today without pouring all the heat in them as they did back then. It is still advisable to re-heat treat.

[Don R]

 You may be correct, there was evidence of a previous primary failure also. There were gouges in the inside of the case but the chain tension didn't seem to change when rotating it.
 I can put a dial indictor on the crank which I should have done before.

 The PO stopped racing it and also didn't terrorize main street any more. He sold off the bored carbs and wheelie bars, Gasahol may have melted the fibermold tank, it's gone also.  I haven't found anyone that remembers how and why the racing ended. This may be a clue. I do know the bike appeared to have had an accident, pegs and pedals were bent forward but no exterior engine damage.

[Don R]

  With the case bottom off it rotates easily, the rings don't appear to be scoring any cylinder. (I feared I had folded an oil ring or something)
  I get .001 of runout on the center main but it seems to be the result of the rod and pistons pushing the crank up. If I rotate the opposite way so the rod and pistons are pulling down forward and backward, I don't see the runout at all.
 I'd prefer to not stretch the rod bolts again if possible. (Aluminum MTC rods)
 This things got me baffled. I think plastigauge on the bearings is next, I assume I need to wash the 20W50 off the bearing halves first.