Will Newgen crankshaft fit in my pregen?

[wankerboy]

Anybody know if it will fit?

[Singh2jz]

Naw..most likely not.

[wankerboy]

Has anybody tried or just thinking it won't.

[cuong-nutz]

It should as long as everything is balanced with it. I'm just making an educated assumption.

[ninjunk]

afaik, the bottom end wasn't changed between years. Obviously you mean a J/K model as opposed to a F model. The 'pregen/newgen' thing is pretty ambiguous.

not sure how well these are balanced from the factory but i'd be sure that you either use the pistons and rods that come with the crank, or get them balanced.


start by checking the part numbers, did ya do that yet?

[choneofakind]

Originally Posted by ninjunk

afaik, the bottom end wasn't changed between years. Obviously you mean a J/K model as opposed to a F model.

Obviously you don't see which section this is in.

Obviously. also, I'm not sure that the bottom end comes as a kitwith crank+rods+Pistons like with 2-stroke dirt bikes. This may have to be done with individual parts rather than a kit.



OP, if you're asking questions like this, I hope you know what you're doing. If you know what you're doing before asking questions like this, you should know enough to go forth and do it. Bruce(random set of numbers) has done a stroker setup on his newgen using internal engine parts from the 300. He might be your best bet as a reference point, but I'm not sure how familiar he is with the internals of the pregen.

[alex.s]

i've heard the pregen and newgens use the same crank and rods but the 300 is stroked out. different heads though.

[micoulisninja]

Bottom end is identical for the pregen and newgen models(as well as other models such as the ZZR250, Gpz250, eliminator etc)...the crank is internally balanced (which means by itself first, then with other moving parts) and a swap can be made...however the pistons are different on the newgen (lower dome resulting in lower compression)
major difference is head design, carb size, front engine mounts, some electric stuff etc...
for increased reliability I would suggest a whole lower bottom transplant if a whole engine is off your financial potential because all the measuring, unbolting, cleaning and bolting back + gaskets, seals, new rod bolts (imperative to use new ones) etc stuff will eventually cost pretty much the same...

I must assure you that going for the 300 bottom will give a nice performance boost but takes a lot of work and knowledge to fit with either the pregen or the newgen 250 head and apart from that keep in mind its chambers and other (mechanical) parts have been designed to work with FI delivery...the 250 are more "indifferent" to that factor...

[alex.s]

Originally Posted by micoulisninja

...however the pistons are different on the newgen (lower dome resulting in lower compression)

i wonder has anyone thrown pregen pistons on a newgen bottom/head combo? does it fit and clear? would this be an "easy" compression increase? i wonder which would gain more CR, thinner gasket or pregen dome piston?

[Racer x]

Never thought about it. But I think the crank and rods would work. The Pistons are different. BUT they might be good for a turbo. They should drop compresson. I will check that. They are cast so it would not be a good idea just a cheap idea

[micoulisninja]

Originally Posted by alex.s

i wonder has anyone thrown pregen pistons on a newgen bottom/head combo? does it fit and clear? would this be an "easy" compression increase? i wonder which would gain more CR, thinner gasket or pregen dome piston?

Alex it is impossible to use a thinner head gasket on either of them...
it is a very thin 0,15mm single layer of metal....
So there are 3 ways to increase compression
a) head milling (which will also bring valves closer to pistons)
b) removing base gasket and use special gasket sealant in its place (which will decrease squish band, that is head to piston clearance and valve-to-piston clearance and practically change the whole shape of the combustion chamber)
c) switch to "plug and play" pistons from newgen to pregen or even better to zzr250's which are optimum for that case and cheap...
stock pistons are always cast...have been proved good enough for low-level natural aspirated mods and comparing newgen to pregen, the later are better if looking for increased performance

a couple of things to keep in mind...
1)when splitting a head from the rest of the engine, a minor milling process must take place for proper surface mating when placing back
2)pistons of higher dome do not have the best flame travel characteristics and require extra advance timing which -in theory- leads to requirements of higher grade of fuel to save from pinging and increased levels of heat on the top of the piston dome

on my previous 250 FI engine I had a combo of all of the above for a base CR of 13,9:1
so I had the ignition curve altered and monitored constantly AFR values which is imperative when practicing such extremes...

[garth285]

Originally Posted by Racer x

Never thought about it. But I think the crank and rods would work. The Pistons are different. BUT they might be good for a turbo. They should drop compresson. I will check that. They are cast so it would not be a good idea just a cheap idea

Just a little info:

The 83-87 has 12.0:1 compression
The 88-07 has 12.4:1 compression
The 08-12 has 11.6:1 compression

The piston pin is the same from 88-12

[micoulisninja]

Originally Posted by garth285

Just a little info:

The 83-87 has 12.0:1 compression
The 88-07 has 12.4:1 compression
The 08-12 has 11.6:1 compression

The piston pin is the same from 88-12

that is indeed accurate, Shawn !

[Racer x]

The compresson ratio is determined by piston shape AND head shape. The first gen head has bigger valves and I funny shape around them. The Pistons are pretty flat compaired to new gen. I am headed out to the shop to check this out.

I cut .010 off the top of the block. I did not want to remove anything from the head as this will go toward the combustion chamber. The head has a 019 service limit, so taking half that from te block worked great. Best thing is JE Pistons

[Racer x]

This is a old don't know the year I suspect 80s-90s on the left and a 2008 on the right. Notice the edges are tight on the older head.

[Racer x]

The old on the left has large pronounced valve reliefs. The lack of material around the side would lower pressure but I think it would make strange squish areas

[ninjunk]

Originally Posted by choneofakind

Obviously you don't see which section this is in.

Obviously. also, I'm not sure that the bottom end comes as a kitwith crank+rods+Pistons like with 2-stroke dirt bikes. This may have to be done with individual parts rather than a kit.

point taken.

so are we calling 2013 to present 'new-er gen'

we're going to be in a real pickle if they redesign it again and we have a 'new new gen' and an 'old new gen' ... or does the J model become 'new pregen'?

[wankerboy]

Thanks for all the info guys, just go by Gen 1, 2 and 300 done should be easy to remember.