How to properly check head clearance.

[Les]

I bought a milled head for my 250r and will be putting the motor back together soon and I obviously want to check the clearance of the head but am not sure the proper way to do it. I have been told 2 different ways 1. put solder on through plug hole and spin motor, that seems to me like you only get a very small area checked. 2. Lay a ring of solder around outside of piston mount head spin motor and pull head to check it, seems logical but wont this ruin the gasket?

If anyone here has done it I would like your ideas on how to do it properly, I want to get as much life out of the motor as I can.

[CR480R]

put 2 pieces in through the plug hole inline with the wrist pin... be sure they reach all the way to the cylinder wall... Dont use solder any larger than .062... Whoever told you to use a ring of solder around the piston was obviously high...

[flotek]

yep^ and do it side to side not front to back as the piston can rock,get several readings and take an average ,i hope yo u rechmabered the the squish band on a 250r the head kinda is goofy

[Les]

Hmm rechambering the head huh. Think I might be in over my head, sending you a PM.

[dajogejr]

Originally Posted by CR480R

put 2 pieces in through the plug hole inline with the wrist pin... be sure they reach all the way to the cylinder wall... Dont use solder any larger than .062... Whoever told you to use a ring of solder around the piston was obviously high...

I use .085 solder no issues on my bike, but...yeah...once on each side parallel to the wrist pin as Denny said...
Measure the thickness and width of the squish.

[CR480R]

Originally Posted by dajogejr

I use .085 solder no issues on my bike

I heard somewhere that the less the solder has to crush the more accurate the reading is... it might not be true but at .040 or less clearance I am not takin any chances...

[Les]

Ok good info so far, thanks.

I am really new to this, so here are a few more questions.

1. Thickness I am looking for about 40 thousandths correct?
2. What am I looking at for a good width?
2a. If it is too wide clean it up with a dremel?
2b. Not wide enough (my guess is it wont happen on a milled head) what to do?
3. I am assuming once the squish is set properly I want to check the compression and if it is too high I need to clean up the center of the chamber to make room correct?

Sorry if these are basic questions, I am really new to 2 strokes and this in depth of engine work. Tore down a rebuilt many 4 pokers in my day so I know my way around the inside of the motor but head work is new to me. I would send the parts out but I am on a shoestring budget and want to get this baby going.

[CR480R]

Originally Posted by Les

1. Thickness I am looking for about 40 thousandths correct?

I run .040 on my 250's with no problems... just be sure your bearings all have tight tolerance... I would try to get the squish under .050...

Originally Posted by Les

2. What am I looking at for a good width?
2a. If it is too wide clean it up with a dremel?
2b. Not wide enough (my guess is it wont happen on a milled head) what to do?

dont touch it with a dremel... use only a mill or lathe.. you want the squish band to at least have the same outer diameter as the bore... if not it needs to be re-cut to match the overbore...

Originally Posted by Les

3. I am assuming once the squish is set properly I want to check the compression and if it is too high I need to clean up the center of the chamber to make room correct?

measure (cc) the chamber volume before making any changes... reference from that

[Les]

Thanks, bearings will all be brand new except for the lower rod bearing. Just waiting on them to start assembly. Hopefully my grandfathers lathe will be able to do the job otherwise I may be SOL. I plan to run VP c12 so 19cc should be about right I think?

[CR480R]

Originally Posted by Les

Hopefully my grandfathers lathe will be able to do the job otherwise I may be SOL. I plan to run VP c12 so 19cc should be about right I think?

the are many builders that can design a head to fit your exact needs... the cost is typically very reasonable.. try flotek..