Ask Redwarf, he had a very healthy 3k motor with 4k crank in it.

Pretty possible, all it'll need is either different rods or pistons.

3k-h block, rods and pistons fitted to a 4k crank.

4k rod at the top

3k-h at the bottom

Back of the block

Counter weight hits the piston towards BDC. As can be seen the rods cap can't be fitted

Past that point the cap can be screwed down. But around the half mark number one rod jams up on something.

I'm not sure what it is can't see anything hitting

Piston sits about 3mm proud

Using a 4k crank and 3k rods it could be as simple as having the crank lobes machined down a few millimetres and use shortened pistons.

You could call it a 3k stroker kit.

Could but i'd think it'd defeat the idea of running the 4k crank but.

Unless your talking about the counterweights.

But i'd sooner just do the pistons. Should be able to find some 75mm bike pistons

charade..................

Could but i'd think it'd defeat the idea of running the 4k crank but.

Unless your talking about the counterweights.

But i'd sooner just do the pistons. Should be able to find some 75mm bike pistons

 

yeah i mean the counterweights... they contact the piston sleaves and a shorter piston may not rectify that issue.

With a 3k running 4k crank and rods. CB Charade pistons look like they'd come close.

 

Level with the block at TDC and are 14.5mm shorter than 3/4k pistons. Come in 76mm plus 20 and 40 thou oversize. Only issue I see is the area for the little end is 25mm compared to the 3/4k of 28.6.

 

Run the 40 thou pistons and you'd have a 1360cc 3k. :) You'd need to do some block clearancing.

Edited October 10, 201015 yr by Felix

i blame the massive hp of k motors lol

CB Charade pistons look like they'd come close.

 

<snipe>Only issue I see is the area for the little end is 25mm compared to the 3/4k of 28.6.

Should be able to get the holes bored out - on-centre, off-centre.

So if I understand correctly I should be able to run 4k crank and rods with some 40thou charade pistons, does anyone make forgies for them?

So if I understand correctly I should be able to run 4k crank and rods with some 40thou charade pistons

 

Quite possibly, I'd be doing some more maths and measuring to be sure. Download the ACL piston catalog and compare specs.

 

Standard 3k's have 75mm bore, the Charades 76mm. So with the 40thou charades would effectively be a 2mm overbore taking you to 77mm.

 

You would have to check skirt to crank clearance, but the charades were 14.5mm shorter. Plus as I said grind the block in places for crank/rod clearance.

 

I do have a feeling though that these are the pistons used in Redwarfs old grunter 3k.

 

Should be able to get the holes bored out - on-centre, off-centre.

 

The piston pin diameters are the same. It is the width of the little end which may be the biggest issue.

Edited October 11, 201015 yr by Felix

is putting a 3kc head onto a 4kc as easy as unbolt them and bolt it on?? or does any of the gear out the 4k head have to be swapped into the 3k head? thanks in advance. oh and what head gasket to use?

Yep, just as easy as that. Don't really have to swap valve train stuff over. But in saying that, there is a few different 3k heads, but in simple terms there's the early heads and the late heads. The late version head is the one to go for, cause of alloy pedestals (instead of cast iron), better valve stems and oil seals.

 

For the head gasket i'd just go 4k, the 3k is the same anyways. If your planning on fixing the 3k head it'd be ideal to work out what vehicle the head came from before getting a valve regrind kit. cause the valve stems and seals are different. But if your going to get the head machined firstly, get them to also replace the stems with ones for a ke70 4k head, their the better ones.

ah sweet! thanks heaps matey. good info!

This is a good thread. I wonder why it died in the arse... maybe more people should post up their 'K' motor builds! :yes: