How much hp/tq can the stock crank and cases take before you start to worry about them failing. I'm considering a Tman 107 that according to the dyno sheets on the site put out in the 120/120 range. If I have to pull the cases and do some crank work, I might as well bore them and do 113 or more.

 

I'm close to going 107 also from my stock 96.

I had my cams [Andrews 26H] done and a TTS with Dyno.

I was 100 ft-lb/89 HP.

I'm going to get the bottom end done, and go DarkHorse Crank. Needed? I don't know, but with the warranty destruction in full, I'm thinking bulletproof motor is peace of mind. Until the Tranny goes. I am just thinking I'll need to do something with the clutch. Did I mention port n polish heads and intake?

When I'm going that far, get the cases bored and go 117"???
I won't be too far off buying a new engine. I've heard to sell the motor, but i was thinking spare motor? Center piece at Christmas dinner perhaps? ha ha

It doesn't end...

As far as an answer to your original question, risks versus reward I suppose. With the crank; save money now, and wonder until the day it happens [or doesn't] or try to go with bulletproof.

If you're pulling the cases apart, I think the dollar value for parts is almost the same. Hmmm I think I just talked myself into the 117"

 

A lot of folks think when torque gets above 120-125 your risk rises sharply.

 

IMHO, if you are going to do any kind of major upgrade to the engine, spend the extra time and money and do the bottom end at the same time. I didn't do it when I put the S+S 106 bb kit and cams in and I am now paying the price. Will it happen to you? Who knows, but as FLHXHS pointed out, it's better to be safe than sorry.

 

Let's here the story as to why you are now paying the price.

 

I assume you have a later model so case boring is not required for the 107" cylinders? Later model = cheesy cranks; send the bottom end to Hoban Brother aka Darkhorse for the Timken bearing conversion; have the crank trued, balanced and plugged (they will weld if you request) and have those cheezy connectiong rods bushed.

Hoban sells "Hobanized" SE stroked cranks for a reasonable price, so if you get caught up in the "go big or go home" thing, you can go really big for not much more money. I like the all bore 107" (early motors). With mild compression, strong bottom end, carbed, .550-.570 lift cams, good exhaust and tune,they are very reliable, pull hard and fun to ride; but that's just me.

 

There seems to be quite a few 107's out there putting up strong #'s and relatively few threads on trashed cranks. IMHO it would depend mostly on how you ride. If bike night wheelie's and hole shots are the plan then definetly do the bottom end but if you're just looking for some roll on power it should hold up fine. I figured when I did my 107 I'd need a whole list of stuff to keep it together but that hasn't been the case at all, SE spring and I'm good to go. About 6k miles since build and it's all good

 

It doesn't take much to slip the later model cranks; a missed gear and high speed downshift; panic braking without pulling the clutch lever; a heat soaked hot start kick back; and there are other reasons. Could happen any time.

I am just saying that if you are building with 115TQ-120"TQ, why not buy some insurance so you can avoid pulling down a $8K build 1000 miles, 5000 miles, 10,000 miles after the build? The MoCo increased the ruout tolerance for warranty purposes from .003" to .012" in '07. Anyone that believes the later model bottom ends are as strong as the earlier years is in denial.

If you are feeling lucky, build her up and ignore the weak bottom end.

 

I've never felt lucky about much but I have felt blessed on occaision. No doubt the bottom end leaves alot to be desired, that being what it is, for my purposes I didn't feel the need for the expense and down time of doing the bottom end. That's just me. I've got less than half of the $8k you mention in my build and I do my own work so if at some point I've got to go for a new crank, it is what it is. Besides, living down here in God's waiting room (that would be Florida) I'll probably get 'T' boned by some soccor mom or squashed by some grandma who can't see over the steering wheel before I trash my crank! No denial there just trying to play the odds

 

$4K or $8K, both a lot of money. I understand playing the odds but I don't like playing against a stacked deck or with loaded dice. Even if your crank does go south, there is still an upside, Hobanize the crank and case bore for 124"!