Interesting thread and even more interesting concept

So for those of you who don't frequent VFRD, the "other" VFR forum, I have been following this thread that may just cause a super-expensive mod for a lot of VFR750s (2nd, 3rd, and probably even 4th gen) a hell of a lot cheaper. I am testing the Trackback feature having linked the thread over there, so let's see if the Trackback works, and if we can pick up some more steam with this thread!!

 

well crap, i dont see the trackback link anywhere....here's the thread in question:

96 vfr750 cbr929 pistons???/ - VFR Discussion

 

Interesting thread.

 

A lot of work and expense for not much power.
Then your sleeves are thinner too.
Better check for offset on those wrist pins.
Valve pocket clearances?

Then jetting and carb adjustments are possible.
Why would you want to do this?

I have seen Honda 160's fitted with early Honda 250 pistons too. So what.
There are always repercussions.

What about the distance from the cylinder head studs and the oil seals?

 

Funny thread, too! I wonder what scrap aluminum is going for these days?

 

this is why there needs to be a proof of concept done first. some of these ideas actually hold water, but just need to be tested and clearances verified before anything gets bolted together

 

You don't need a proof of concept. You need someone who knows what they are doing , how to read a mic, how to add and subtract. Want to know the thickness of the bores? Sonic test them. They are talking an over bore of a .160". What the hell do they think they have 1/4" (.250") thick walls?

One guy is talking about maybe using new rings?? WTF was he going to use, used ones? Talk about piston hitting the head was no big deal. Just grind the piston down?? They call it a fly cut or milled top. DEPENDING on thickness and under support. Might get it balanced. Might!! Eyeballing the wrist pin location?? Eyeballing?? Thinking 1mm is no big deal. eerrr that's .040", which is a lot! (also a normal overbore size) And they want to overbore .160"??? Not even to mention about the larger valves of what 1mm? Do they even know what it takes to change valve sizes .040" larger. Let alone the characteristics that will change, like port flow & velocity with that much!! I hope someone has a Winona head machine or the like.

Then someone shows a photo of a broken ring land on a piston top and states it's from cutting it to thin..?? Not even close. That piston broke because the ring gap was to small for the heat in the chamber/piston top. Do you even know what ring gap is?

These guys are going to do an overbore/rebuild on a motor that turns 11k redline and they are using flintstone tools with neanderthal knowledge. Yea I know, even a caveman can do it!!!ray:

They need to search out someone that's very knowledgeable about building modified engines with a proven record (not just some guy with wrenches and bench grinder) if they want it to last more than a few hours or may be days. A guy like Dave Dodge. He seems knowledgeable on the V4 motors.

 

This post answers most Donald's questions about the cylinder walls.

I haven't read every post. I still think it's an interesting topic, regardless of the possible outcome.

96 vfr750 cbr929 pistons???/ - VFR Discussion - Page 2

 

I have worked in motorcycle shops where mechanics were always swapping engine parts, pistons, cams, carbs, you name it.