Hey, pulled apart my 4k to change the head gasket and found these pistons, done a bit of a search and think they may be 4k-u ones? can anyone tell me for sure / tell me if theres any benefit or downside to them.

 

Cheers, Jason

Edited April 28, 201016 yr by jason12

Yeah they're 4ku pistons. Aparently 4ku's (if it is the whole motor) had a bit more grunt than our ADM 4kc's.

They are the 4k-e or twin squish type. Jap import motor you have there. Shares same head as dished 5k.

 

Downsides none, unless you try to get replacement pistons.

 

Upside, they make more power than the normal flatop motors.

Sweet, cheers guys!

there are two types of 4k dished pistons.. the first one is just like those in my engine.. my engine is a 4k-II twin squish with electronic ignition. the second type is with valve holes just like 5k ones...

Hmmm, I've not seen 5K's with valve reliefs in the pistons though!? They'd have to be aftermarket.

Same here. My 5k has the D shaped dished pistons.

 

I've had a few 4k's with dished pistons.

 

The ones with the D shaped dish were supposedly 4k-u when I researched going by the numbers on the inside of the piston.

 

The twin squish (or ones that look like they have valve reliefs) were 4k-e by the numbers on them.

 

I've had one 4k with the D pistons and two with the twin squish pistons.

 

EDIT: Found a pic I took of the two 4k dished type pistons:

 

part no. on left piston is 13101-13020 4k-u type

part no. on right piston is 13101-13022 4k-e type

Edited April 30, 201016 yr by Felix

Is there any way to tell if the whole motor is a 4k-e?

it should say on the side of the block mate. from memory if you are looking at the motor it is on the left hand side at the back? if I'm wrong please correct me.

It won't tell you what model the motor is on the engine number.

 

Usually there is a sticker on the timing cover, but it could have fallen off over the years.

 

The motor with the pistons on the right in the pic I posted had a 4k-e sticker on the timing cover when I got it.

my engine had a sticker on the valve cover which tells you to use only long spark plugs and not the typical ones just like those in the picture...the other one had fallen off...

Now being that is engine is different to the std 4k's... could i still put a std 3k / 4k head on? If so how much could i have shaved off? Also is the usual 20 - 60thou off still applicable for the 4k-e head?

Now being that is engine is different to the std 4k's... could i still put a std 3k / 4k head on? If so how much could i have shaved off? Also is the usual 20 - 60thou off still applicable for the 4k-e head?

 

Because its a dished piston motor it has a head with a shallow combustion chamber just like a 5k head.

Using a normal 3/4k flat top piston head will give you a low CR.

Ah yes that makes sense, cheers. How much would you reccomend i have taken off the head on it now then. Only mods will be an exhaust and gemi carby... I'm guessing 20thou would be ok?