Flat Top Big bore Vs Standard Big Bore

[FL-cracker]

Well, I was all stoked to start putting my TLR Freestyle ported 85.5mm flat top piston motor together untill talking with Kevin at LegDrag yesterday evening for about 45 minutes. I realy rushed into buying the parts for this motor before thinking everything through.:banghead: I am basicly left with a cylinder that is on its last bore.:banghead: When I bought the cylinder I did not realize that the sleeves had been milled down instaed of needing to bore the cases. So After this fresh cylinder and pistons are toast i will need to have new sleeves droped in and have the porting matched up. I paid $900 for the fresh cylinder, new pistons, and a greater Yamaha head. Seemed like a fair deal. New pistons are? $400 a set
sleeves and bore? $300
greater yamaha head? $350
port job? $350
.......................................................$1400 total If i had the work done my self, so the price seemed fair.:sneaky: But I figured I would be able to bore over to 86mm, untill seeing that the sleeves had been milled down.

My main question though is what kind of longjevity can I expect from this motor??? Kevin mentioned that the shorter pistons will have more slap, and will proabably need a rebuild 3x faster then regular pistons. From everything I heard this motor will realy rip, so I will probably just build it anyways even if it does become a total loss after 4 months. I burn 5-7 tanks a gas a week, so I realy proabably should have built something not so on the edge.



I post this thread to come to a desicion on weather to build the motor I got, or sell it, and build a "JR" standard piston big bore.

 

[FL-cracker]

oh, and make sure you listen to kevin. do whatever he tells you to.

he is the man.

I would, but at the end of the conversation, we were both just kinda like :dunno: Unless someone wanted to give me $600 for the Cylinder and pistons, I may as well just run the motor. Or else I will be spending more dough on lesser of a motor. :banghead:

 

[Rickster]

My main question though is what kind of longjevity can I expect from this motor??? Kevin mentioned that the shorter pistons will have more slap, and will proabably need a rebuild 3x faster then regular pistons. From everything I heard this motor will realy rip, so I will probably just build it anyways even if it does become a total loss after 4 months. I burn 5-7 tanks a gas a week, so I realy proabably should have built something not so on the edge.

Why would the shorter pistons have more slap than regular pistons? That does not make sense.:dunno:

I do know that Waterfreak ran a bigbore with flat top pistons in his beater ski for a year, and the pistons and cylinder looked brand new when he took them apart.

 

[FL-cracker]

^^^^great news!.....I cant answer your question as I am not a engine builder. I kinda thought it made since though just because the pistons are shorter, will have a tendency to slap more. dunno

 

[Idok]

oh, and make sure you listen to kevin. do whatever he tells you to.

he is the man.

i got a 10 minute lecture when I asked if he had read my sbt experience thread :frown:



:biggrin: (for real though)

 

[SUPERTUNE]

The shorter Kawasaki flattop pistons don't rock as much in the bore due to the wristpin located more centered in the piston compared to the 701/760, that is a little too low in the piston.

 

[Rickster]

The shorter Kawasaki flattop pistons don't rock as much in the bore due to the wristpin located more centered in the piston compared to the 701/760, that is a little too low in the piston.

That's what I heard... Thanks for the clarification.:hail:

 

[WFO Speedracer]

So I am gatherin that you are using Kawi 750 small pin pistons without any mods, Is that correct?

 

[waterfreak]

I liked to say that if you use an high grade synthetic oil such as 927 or klotz, you should have no problem with longevity. Do you know what the squish is set at? What is the cylinder/ piston clearance (should be no more than .005) and of course your compression .

All I can say is that I was amazed how my flat top motor looked like after 1 year of running the piss out of it!:highhorse: You'll love this motor...trust me ! Just keep the compression mild (about 175 psi)

Oh, and very importantly, make sure that all your port are chamfered properly!!! and you are using the 20mm pistons pins :biggthumpup:

and make sure you listen to Kevin!:woot:

 

[FL-cracker]

Thanks for the reply guys. I will take a look at the pistons tomorrow, I was told I can use Kawi pistons, but Im not sure wich they are. The motor is setup for 200psi so I may have the domes cut. I dont know the exact squish untill I put it together. Project should be under way this week.

I will have my custum stock hood pics up tomorrow when I get off work. My bud got a new digital. From the middle of the bar end to the top of the bond rail measures 12 5/8s". I am very impressed on how it is coming along.