Im rebuilding my 131 again and trying to decide if I want to do another 131 or go smaller. This time I will be doing T Main sleeves fitted to my pistons. I have a Dark Horse Man-O-War crank that is balanced for 530g pistons. I can get pistons for 130 4.280 or 131ci. 4.310. I might be able to get 128 4.250 pistons but they dont list them. They list 107 to 128 pistons i think by mistake. The T Man sleeves are much thicker but the spickets still have to fit the bores of the case so the 131 spickets will be very thin. 21 Low Rider S. Im not racing just a street cruiser muscle bike. 93 octane CR515(could change) cam SE Extreme heads 64mm tb ported manifold, 6.8 injectors Jack Pot Riot exhaust.

 

I’m trying to keep up best I can with the M8 builds and best practices. I’m interested in many ways in the M8. If there are other threads from you, I likely missed them.
Why are you building your 131 “AGAIN”?
What happened to the previous 131?
How many miles did you get from it?
What went wrong?

This isn’t a mischievous or negative inquiry, I’d like to build an M8 carb’d in a new softail frame and use the morris magneto kit bypassing all electronics. All engine families have failures and issues… I’m not faulting the M8.. I’m just trying to keep educated with out rose colored glasses as to the pro’s & con’s. I’ve gotten a negative reputation for pointing out that evo-M8 all make about the same power per cubic inch.. I don’t say that to put down the M8.. it’s just a realistic reality check. In stock case form the M8 has in my opinion, huge advantages over previous engine families.. but when you include aftermarket cases they are all pretty much equal. As M8 prices depreciate they will become attractive to me as a build platform.

So please share what has brought you to this point? This forum caters to new and most use their wallet and just repeat what their engine builder tells them. That isn’t the perspective I want to follow. Real world I want to know what goes wrong and why?

”usually” with Shovel & EVO the bigger the bore the less surface area for base and head gasket sealing.. so often a detourent to the larger bore solutions are a greater potential for leaks… Second, larger bore seem to create more heat.. surface area friction, thickness heat dissipation…? Did you have engine temperature challenges? What target rpm did you have in mind when building previously? An example when I was deciding on what aftermarket EVO to build.. I considered the pro’s and con’s of the 127, 131 & 140 inch builds. I quickly ruled out the 140 because it’s just the 127 with a 1/4” larger bore. I deemed that as just too thin for my target use.. daily ridden 150 RWHP that could stay together 40,000-50,000 miles between ring replacement. I decided at the time (but later bought parts for a future) 131 just to save the stroke and keep piston speed and skirt area that much more forgiving. In truth the difference in stroke between the 127 and the 131 are probably not that big a deal in regards to longevity. The 10 extra hp potential would have been nice. On the other hand.. the shorter skirt for the larger stroke also creates greater potential for pistons sticking and increased ware due to rocking… it also pushes the oil rings closer together.. so at the end of the day the 127 seemed a better balance to achieve my goal.

 

Is this the 3rd time you're rebuilding your engine within the last year or two? Maybe you should reach out to someone like TMan and follow their advice.

 

He likes R&D and apparently can afford it as a hobby endeavor!

This is an interesting discussion, and I am looking forward to everyone's input.

Personally, I have let go of my long-time mantra of "no replacement for displacement."

I realize the parts need to complement each other in order to synergize optimum performance.

I try to set my expectations by studying Dyno results and looking at what has been put into the build.

I enjoy acceleration! It puts a spontaneous smile on my face, and I consider it essential to highway safety when riding on two lanes in the twisties by minimizing my exposure to the risk of opposing traffic when passing opportunities are limited.

Having said that I also think performance needs to be balanced against reliability.

 

i sent him a email too. yes 3rd all because no one around here knows what they are doing. Bad tune destroyed my 128 when it went lean in the cold and didnt have the correct cylinder wall clearance. It was a drop in kit put together by the tuner. Number 2 was a HD 131 crate motor that was tuned too rich and washed the cylinders. Number 3 i havent taken apart yet but I paid a shop to check all clearances and gap my rings. Looks like the rings touched in the rear cylinder because it looks like this. I didnt tell him to put the rings on the pistons but he did. I should have taken them off and double checked them but i didnt. This time i am going to a known pro. T Man will be fitting my pistons to his sleeves and gapping the rings. No I cant afford it. but its either fix it right or junk a bike that i have dumped alot more into then just the engines.

 

I'm sorry for your misfortune on those builds and I'm sorry for misreading your situation. Please accept my apology and I hope Tman gets it right for you!

 

Man, I hate to see this!

I have my FM 128 that I put together, and it has been an absolute sweetheart.
I want to go 132, but this engine has been so great that I read tales like yours, and worry that it could all go to hell.

I am going to check my runout, and this will be the deciding factor. I keep putting this off, because I am afraid of the reading on that dial!

I just want a little bit more top end power…

 

How many miles do you have on your 128?

 

30K

 

With M8’s do they weld the cranks solid for large builds? I welded my evo style 127 crank. It does help with keeping the crank true. I’m hoping for 40k-50k out of my top and 60-70 out of the bottom…. But hoping and achieving are likely far apart.