Question on +2mm Crank

xxx

Member
Messages
21
Hi guys

i just took my engine apart i got
+2mm crank
and 28.5 big bore kit

i got the 1mm copper gasket to but on
do i need to put and the stock gaskets as well?
thanks :p
 

waqr

Well-known member
Messages
581
Location
Sweden
Well, if your cylinder is not machined for the +2mm crankshaft then you need the 0,020" and the 0,040" gasket in order to get proper squish.

When you say that you have the 28,5cc big bore kit I assume that you mean a cylinder with a 36mm bore. This in combination with the +2mm crank will make your engine 30,5cc and not 28,5cc. You can only get 28,5cc by using the 36mm bore cylinder together with a stock crank (28mm)
 

xxx

Member
Messages
21
yes thats correct 30.5 36mm, thanks very much
its not machined and i used the 0,040 only, is that a proplem?
the 0,020 is the stock gasket?
 

waqr

Well-known member
Messages
581
Location
Sweden
Yes, the 0,020" gasket is the stock one. The main thing is to see that you get the proper squish clearance with the gasket you are using. Normally you need the stock one (0,020") and the 0,040" gasket to get proper squish with the +2mm crank (when used on a cylinder that is not machined for the longer crank) but it might not always be the case.

The best thing is therefore to always measure the squish after you have assembled the engine. I would say that you should have a squish somewhere in between 0,017" - 0,021" roughly. I wouldn`t go under 0,017" anyway.
 
Last edited:

xxx

Member
Messages
21
thanks a lot buddy, i just got them together i will start her tommorow
 

EL BARTO

Well-known member
Messages
1,501
Location
Sydney
Just to check,are you running a zenoah 4 bolts or the stock cy 2 bolts?
The zenoah have more clearance from factory,so even with a +2mm crank,you won't need to stack gaskets.
If I remember correctly,I got away by only using a 0.020 copper gasket and I still had about 0.018 clearance at the top,so by only using the 0.040 gasket you bought,you should still be fine.(remember to use a bit of sealant with the copper gasket).
 
Messages
14
if you check the squish properly, you might not need to stack gaskets, i just put a 1mm stroker in my engine with a 0.005'' gasket, thats the smallest one, and i've still got 0.018'' squish. From what i've been reading you want about 0.015'' with 0.012'' being the min. An easy way to check is to get a bit of solder bend it in a L shape take the spark plug out feed it in so it sits across the top of the piston, make sure u still have hold of the solder, and slowy turn the engine over might take a bit to crush the solder at the top. Then take the solder out and you'll notice that the solder has been squashed by the piston, measure the squashed piece and see what you've got. Think you might be suprised a 0.040'' gasket might do, will have some good compresion thought might need to run a higher octane fuel
 
Top