Long rod 4mil vs. stock rod 4mil

[Atomic Monkey]

Opinions wanted!

 

Is there a big enough difference between the two that it justifies spending the $$$ on a long rod 4mil if you already have a stock rod 4mil?

[Deadbeat]

i would run whatever you got if its brand new, do a long rod next time

[shanYE west]

^^  That.

 

Also.. piston availability is going to be better with the stock rod.  Lots more options. 

[Strm Trpr]

http://www.wiseco.com/ProductSearch.aspx

 

795 series pistons are required when running 115mm rods.

Piston size increments are 0.5mm or .020".

 

110mm rod piston diameter increments are 0.25mm or .010".

 

Rod to stroke ratios for the 4mil stroker using 110mm rods vs. 115mm rods is 1.9 vs. 2.

 

You get slightly less piston side loading with the 115mm rods, but the difference is negligible.

 

With the 110mm rod, you get slightly faster piston speed which translates into better cylinder filling vacuum.

 

With the 795 series pistons I'd imagine the piston is slightly shorter in overall piston height due to the wrist pin being raised 5mm to accomodate the extra 5mm longer rod and the piston would be slightly lighter.

 

If your not drag racing requiring ultimate top end rpm and power, run the 110mm rod 4mil stroker crank.

 

Obviously any motor builder will know better, so I'd consult with them as well.

 

Just my $0.02.

[Atomic Monkey]

Thanks, that is great info there!

[sheerider11]

Do not go short rod.

I had one. Had. One season my cylinders were egg shaped. You could see the excessive wear front and back.

I now have a 115. Couldn't feel a difference in how it revs.

I ride just about every Sunday maybe miss a few here and there. So my season was 4-5 months maybe. So give or take 100-150 hours.

[Atomic Monkey]

If I didn't already have the short rod crank, I wouldn't buy one. Although the the available piston sizes for the long-rod are somewhat discouraging. I thought the post about the rod ratios was great, and it's what helped me make up my mind. 

I made a trade and thats how I got this quad, otherwise I've always riden dirtbikes. It came with the Short-rod in it, and I don't know how long it was run before I got it, but I know there's at least one good season on it. There's a few months on the ice, a summer where we put hundreds of miles on, and quite a few field beats.

The head gasket leaked, and one of the pistons melted to the cylinder last December. Neither cylinder has a ridge at the top, and the cross-hatch is still visible in the good cylinder.

For now I'm just going to stick with the crank I have. When it breaks, I'll put the money into even more stroke.  

 

Sheerider... its probably a difference in riding styles. I'm riding with all 4 pokes, and mostly idling down the trails. One guy got rid of his Banshee for a 450R and regrets it. The other group I ride with, one of the guys just picked up a Banshee... so at least now I'll have someone to race to the gas stations!

[Strm Trpr]

OP, what are your plans?

Do you know why the piston burned down and seized to the cyl?

If it were me, I'd split the cases and have the crank checked out for damage due to the piston seizing in the cyl.

Have the cyls mic'd for roundness and if able, go to the next .010" overbore with new pistons.

Get the trans pro mod'd by Redline and the upper case port matched to the cylinders.

Are the cyls ported?

When you reassemble the motor do a leakdown test to ensure there are no air leaks.

Disassemble the carbs and remove all jets.

Clean them with carb cleaner and blow every orifice out with compressed air.

Make sure your floats are set to 20+/1mm.

What jets are you running now and what is your complete mod list?

[Starwriter]

Weren't you the one that was going to run 795 pistons with short rods? How did that turn out?

[Atomic Monkey]

The crank looks good, no extra slop or rough spots when spun. I'm pretty certain it was the head gasket leaking that washed down the cylinder... the exhaust was nice and clean, and there was coolant in the pipe. I have a different thread going on the porting, and am close to being finishing.The cases are also getting split to take a look at the trans... having some problems upshifting in the higher RPMs.

And yes Starwriter, I am that guy... gave up on that 795 idea. Kept getting conflicting info, and I know the stock offset works. But I'm still thinking the 795 would put me -3mm below deck and the -7mm on the bottom. Not sure if there would be an interference problem with the crank. Be good to see if its possible... I'm still curious.

Since I need the cylinders bored, I've started calling around, because I also want the porting I've done checked and/or touched up. This latest deal with the crank was brought up by a builder because he's not as familiar with the short-rod setup. The way it was explained, it would just be easier to setup around a long-rod crank. I can't justify spending the $$$ just to make it easier, so I was asking to see if there are any other major benefits. If I stick with the short-rod, he wants the whole engine, and there goes the time I want to spend digging through the trans while the cylinders are out.