125-200cc Squish band for a 144

[rockdancer]

I have been contemplating getting the head shaved on my 144.
I still feel after doing Cr Ignition and Keihin PWK swap there is something lacking in its performance compared to a CR 125 that I rode which had a higher compression ( which was obvious when kicking it over)
I was always thought it sounded like a bit of a radical or possibly unreliable modification .
Reading more about it and hearing results on this website it seems that its more about getting the the fuel to burn more efficiently around the outside of the piston as well as the main fuel charge in the middle . Thus adding extra charge and power. This seems to be in the low to mid range.

A standard OEM 144 seem to run at fairly low compression - well mine did anyway . I think it was 145 lb its now at 140lb.
Looking at my piston after 20 hours or so it has a high build up of carbon which I believe can also be a sign of inefficient burning ( and rich jetting ofcourse)

Checking the squish band it appears to be around 1.5mm - possibly higher. I need to get an electronic measuring caliper tool tomorrow.
It seems to be that due to all the different tolerances between the crank, shaft and piston and head they like to allow a fairly large tolerance. It is up to fine tuning to bring the bike to where it should be.


Reading various different 2 stroke tuning guides some people talk about a squish that is at or well below 1mm ( .04 inch ) .
I am going to get the head shaved to give 1mm squish thickness or possibly lower.

Anyone recommend a thickness ? - I d like mine to run on normal hi octane pump fuel
I am thinking around 175 lbs is on the compression.
Anyone like to add to this or give advice.
Thanks.

 

[wallybean]

A couple of things. First you don't want to go drasticly smaller than .040"(~1.0mm). At some point you get to where the squish is so tight that it becomes innefficient and runs a risk of build up causing problems. Ideally I like to keep the squish at between .040" and .038". Next I have found that the 125 head can be susceptable to warping the more you take off the deck. Proceed carefully as if you have any over heating or water hammer type event the head is liable to warp more than if it is stock thickness.

One thing I would also do if you want to help performance is get the rear transfer raised to the same height as the 125 cylinder. Husky is taking 125 cylinders and boring out to 58mm. This lowers the rear transfer ~2-3mm. Get someone that is competent with a diegrinder to bring it back up so that it shares the same timing as the other transfers. Definitely helps breathing. Lastly, I would consider having the power valves themselves re-cut to the same lower edge height as the CR does. They use different valves and the WR's are quite a bit more conservative to make the motor more pathetic....I mean tractable on the bottom/early mid.

Good luck and keep us informed on how you progress.

 

[Blakelpd5]

Sorry to Hi-Jack, but Walt, you are awesome! So nice to be able to come here and get info from a guy like you.

 

[CelticDude]

Walt rocks! You might try a Scalvini pipe. It made a huge difference on mine from mid to top without any other mod.

 

[rockdancer]

A couple of things. First you don't want to go drasticly smaller than .040"(~1.0mm). At some point you get to where the squish is so tight that it becomes innefficient and runs a risk of build up causing problems. Ideally I like to keep the squish at between .040" and .038". Next I have found that the 125 head can be susceptable to warping the more you take off the deck. Proceed carefully as if you have any over heating or water hammer type event the head is liable to warp more than if it is stock thickness.

One thing I would also do if you want to help performance is get the rear transfer raised to the same height as the 125 cylinder. Husky is taking 125 cylinders and boring out to 58mm. This lowers the rear transfer ~2-3mm. Get someone that is competent with a diegrinder to bring it back up so that it shares the same timing as the other transfers. Definitely helps breathing. Lastly, I would consider having the power valves themselves re-cut to the same lower edge height as the CR does. They use different valves and the WR's are quite a bit more conservative to make the motor more pathetic....I mean tractable on the bottom/early mid.

Good luck and keep us informed on how you progress.

Thanks Walt .
I was nt going to bring up the port timing issue - thats next on my list but since you have and given some advice there thanks very much. I have limited options for local guys to do the work.
Porting seems to be a common mod on CRs that are raced but havent seen much of it discussed here.
I didnt know that about the CR power valves . I am not sure if the OEM 144 kit I bought said whether it was for a WR or CR - I guess its not easy to tell the difference?

Celtic Dude - yes that Scalvini pipe is further down the list but getting closer

Thanks again

 

[rockdancer]

I thought I'd post a couple of pics of the top of the piston
It seems like a fairly even coating with some bare patches on intake side
There is also what looks like a wear mark on the side of the bore near the exhaust- didnt notice that before . Not sure if this is normal.
Also burnt oil/fuel residue on head seems to be towards the exhaust port side - I guess this is normal

Is it worthwhile cleaning the carbon from the top of the piston ? Whats the best way to do this?

 

[dartyppyt]

While ya got that apart. Use thinnest base gasket for more torque, largest for lil less on bottom but lil more up top.

you ought to send cylinder/powervalves/head to Walt so he can fine tune her. Good pipe will wake it up as well.

 

[rockdancer]

While ya got that apart. Use thinnest base gasket for more torque, largest for lil less on bottom but lil more up top.

you ought to send cylinder/powervalves/head to Walt so he can fine tune her. Good pipe will wake it up as well.

I know I know . I will try this and the FMF fatty pipe thats coming and If that still not doing it for me I think it will be 165 time LOL

 

[wallybean]

Thanks Walt .
I was nt going to bring up the port timing issue - thats next on my list but since you have and given some advice there thanks very much. I have limited options for local guys to do the work.
Porting seems to be a common mod on CRs that are raced but havent seen much of it discussed here.
I didnt know that about the CR power valves . I am not sure if the OEM 144 kit I bought said whether it was for a WR or CR - I guess its not easy to tell the difference?

Celtic Dude - yes that Scalvini pipe is further down the list but getting closer

Thanks again

Actually in the oem kit all the power valves are the same. It is the 125 that they are different. My bad as it was after a couple of toddies when I posted. They are still a little conservative with their timing.

 

[john01]

Hey rock I finally got the Fatty comming your way sorry for the delay. Anyway I put the tracking number in a PM to you. The Fatty helped my CR125 and 144 pull faster through the rpm's and picked up a liitle power too so it might be what you are looking for. If not next option is a SC/Lectron and the grand daddy WB165 if that still doesn't do it.

 

[rockdancer]

Hey rock I finally got the Fatty comming your way sorry for the delay. Anyway I put the tracking number in a PM to you. The Fatty helped my CR125 and 144 pull faster through the rpm's and picked up a liitle power too so it might be what you are looking for. If not next option is a SC/Lectron and the grand daddy WB165 if that still doesn't do it.

Thanks John you are a gentleman. The good guys and generosity on this website never ceases to amaize me.

The squish thickness was'nt as large as I first thought - it was approx 1.3mm
I got the head machined .35mm and retested it and the squish measured 1mm. I was thinking it would be .95.
It was $50 for machine only and in typical poor local service style he commented on the job being "a pain in the arse".

The compression went up from 140 to 155.

So far from riding it up and down the street the difference isnt very noticeable. It may be a tiny bit more responsive at first 1/4 throttle. Hard to tell . I will be going for a proper ride and my first decent ride with the CR ignition tomorrow.

 

[john01]

You are very welcome .

 

[MotoMarc36]

Thanks John you are a gentleman. The good guys and generosity on this website never ceases to amaize me.

The squish thickness was'nt as large as I first thought - it was approx 1.3mm
I got the head machined .35mm and retested it and the squish measured 1mm. I was thinking it would be .95.
It was $50 for machine only and in typical poor local service style he commented on the job being "a pain in the arse".

The compression went up from 140 to 155.

So far from riding it up and down the street the difference isnt very noticeable. It may be a tiny bit more responsive at first 1/4 throttle. Hard to tell . I will be going for a proper ride and my first decent ride with the CR ignition tomorrow.

People on this site are generous and awesome!

.040 is a great number but squish isn't the end-all of 2t cylinder head design. The job you had done probably did help overall, but there may be more to it. 155 is pretty safe in general even with a poor design, I'm suspecting he just cut the gasket surface ( a pain?! Really ? ). There may be benefit to cutting it even more, then correcting the squish thickness and width, giving you a bit more compression with the same squish measurement... best to leave it to someone who understands the science behind this particular motor, not some whatever machinist (not saying your guy is?).

 

[jo360]

mines got the 144 kittedcr engine using hi temp copper silicon as a base gasket and produces around 185 psi cold, you can retard the ignition slightly running higher comp as the fuel burns quicker.
140 psi seems very low.

 

[rockdancer]

mines got the 144 kittedcr engine using hi temp copper silicon as a base gasket and produces around 185 psi cold, you can retard the ignition slightly running higher comp as the fuel burns quicker.
140 psi seems very low.

Do you know what your squish is?

I rode it today and after playing with jetting its ripping pretty hard now, the combination of cr ignition
& 144 kit are now working well. I rode with the 36mm keihin and it was too lean . Didn't have jets so swapped back to mikuni and with needle adjustments its running really good. I think I will leave it on.
Still getting a creamy substance in carb.

 

[jo360]

i will double check and let you know the squish,..creamy substance can only be one of two things water or you really love your bike.

 

[jo360]

measured squish this morning using solder and verns the band is exactly 1mm wide put the gauge on and gave her 4 kicks with throttle wide open 175 psi stone cold wearing a set of sneakers.

 

[rockdancer]

quote="jo360, post: 278102, member: 3386"]measured squish this morning using solder and verns the band is exactly 1mm wide put the gauge on and gave her 4 kicks with throttle wide open 175 psi stone cold wearing a set of sneakers.[/quote]
Thanks . Mine is 155 now. Which is what it was when new kit put on. I guess your piston is a tighter fit?

 

[jo360]

check your exhaust bridge area on the cylinder it may have been cut to allow for expansion, i also drilled the piston to allow more cooling to this area.

 

[rockdancer]

You are very welcome .

Got the pipe today and had it on within an hour of getting home
Looks fantastic -thanks again John
Took it for a quick spin up the road in the dark and all I can say is wow !
Straight away the front wheel is up without trying and this thing has woken up. Big time
I can't wait to take it for a proper ride again
The bike also sounds tinnier
I think My old pipe was restrictive and this was just the ticket

If you have a standard Pipe the FMF fatty pipe is a must do as far as I'm concerned
It also fitted up to standard muffler which is great

I also adjusted the power valve lever all the way up from 3/4 setting and that seems to be working better too