701 Flattop for Surf ?

[_KrashCørps_]

I just recently joined the X and as this being my first thread. I wanted to touch on my motor.

I just acquired my first Yamaha motor and I was going to keep it simple for starters but little did I know this isn't a normal 701. This is a ported flat top on it's last bore, 85.5 flat top pistons and requires flat top domes.
A lot of my Freeride friends have told me to sell it and get a fresh ported 701. But all my race friends are telling me I would be out of my mind to go to a regular ported 701.

So what are your guys thoughts on this? I am working on my first surf build Krash Predator.

A little more info on the motor:
62T bottom end
61x Cylinders

 

[speedysprocket]

Welcome, bud!


Sent from my iPad using Tapatalk

 

[jackmarcus]

Keep it and try it, if you don't like it then yank it and sell it


Sent from my iPhone using Tapatalk

 

[Nuklear6]

If it's set up right it will kick a$$. Flat tops direct the force of combustion directly down into the crank shaft (the whole object of internal combustion engines). Dome tops tend to direct some of the energy from combustion out towards the cylinder walls.

I say if it's set up right because there have been many failed attempts at flat top yamaha motors. Combustion chamber need to be right. .

Chuck Palmucci
CPT Enterprise LLC
609 510 3062

 

[_KrashCørps_]

Great! I'm unsure of the hours on the crank but it doesn't feel loose in the slightest. Do you thInk it would be unwise To run it without a rebuild?

 

[Yami-Rider]

You say the crank doesn't feel loose.. so I assume it's apart?

 

[_KrashCørps_]

No it's still in the case.

 

[Yami-Rider]

You can only truly inspect a crank out of the case. Did the motor have good compression? Ideally it would be best to rebuild the motor, specially since it's the off season and you don't know the history of the motor.

 

[_KrashCørps_]

Yes the compression was fine. I will definitely be rebuilding the motor but I was wondering if I should replace or rebuild the crank. That's the expensive part and I wasn't looking forward to having it replaced or rebuilt Although i'm not looking forward to a rod destroying the entire motor either...

 

[Yami-Rider]

If you know how to inspect it, pull the crank and look it over or a rebuilt crank cost 250 from JetManiac. Definitly want to replace cranks seals at the very least.

 

[cookn]

there are only two options for a unknown hour crank. replace it or run it. If I run an unknown hour crank I do pull it out of the cases and check both ends with a dial indicator to ensure its still true and the check all bearings for any signs of rust or unusual noise, but its a gamble either way in my opinion, just a choice of which lets you sleep better at night. spend the money and possibly replace a crank with many seasons left on it or run it and risk wrecking a bunch of engine parts. If it was an all stock motor I would say run it, but you have 61x cylinders that have been re sleeved and most likely custom cut domes, so not just off the shelf parts that can be easily replaced. just my 2 cents, hope it helps

 

[_KrashCørps_]

Thank you guys for all your inputs, I appreciate it!

 

[iangdesign]

Run it till it blows...then rebuild engine.