Planet Minis

dixon · 12-29-2009, 04:58 PM

I am wanting to mill my 87 ysr head. Bike is mostly stock except jet kit and reeds. Bike has 1,000 miles. Just wanting a little crisper without sacrificing reliability much. How many thousandths should I take off?

daddysmut · 12-30-2009, 05:54 AM

i have a milled head on mine but i bought it pre-done. if you really want to wake the YSR up go with a pipe and carb

firepower354 · 12-30-2009, 05:55 AM

.030 is safe, and adds a nice snap to the low end.

dixon · 12-30-2009, 08:13 AM

Thanks, 30 it is

johnson05 · 01-06-2010, 05:53 PM

You should set the squish properly. Say .85mm to .90mm. Check it with solder to be sure. The problem with older bikes is previous owners might have milled the cylinder or head. Sometimes guys will mill a thou off the top and bottom of the cylinder along with the head just because the surfaces do not sit flush. My engine builder even likes to drill and put alignment dowels on the cylinder just to keep everything lined up a little better. A little bit of solder is cheap. If you shave too much off that ain't going to be cheap.

dixon · 01-10-2010, 08:09 AM

I was wondering about squish. How do I use the solder?

Kurlon · 01-10-2010, 08:24 AM

Basically, you assemble the motor with pieces of solder set around the edge of the piston, on the dome, etc. Turn the motor over a couple of times by hand and then pop the head off. Each piece of solder will be compressed from where it hit the head. Measure each piece, and note the thinnest you find.

That measurement is what you use to determine your 'squish' value. Because you're using solder you can't use that measurement directly though. Solder is slightly elastic and 'springs back' when you take the pressure off it, so your actual squish value will be a touch less than the measured value. There are tables online that will convert from measured to actual squish based on the size and type of solder you use.

You can also use clay/play-doh or get packs of wax strips made just for this purpose. The wax strips come in various colors, with the idea that you get the squish setting you want, and the next size up and down from that. When you test, you want to see the next size up squished, your target size just showing contact, and the undersized piece untouched.

firepower354 · 01-10-2010, 09:52 AM

There's also rod elasticity, and multiple bearing clearances to take in account when the piston is rounding the top of the stroke.

dixon · 01-11-2010, 05:14 PM

Holly cow. I am original owner. Wish I could just take thirty thou off and call it a day.

firepower354 · 01-11-2010, 07:54 PM

I'm sure you can. Yamaha was generous with clearance. Pull the head and base gaskets, bolt the jug & head on, and see if it hits. Work from there.

12-29-2009, 04:58 PM	#1 (permalink)
dixon PM Newbie Join Date: Apr 2009 Posts: 49	Milling YSR head I am wanting to mill my 87 ysr head. Bike is mostly stock except jet kit and reeds. Bike has 1,000 miles. Just wanting a little crisper without sacrificing reliability much. How many thousandths should I take off?

12-30-2009, 05:54 AM	#2 (permalink)
daddysmut 3rd Gear Member Join Date: Dec 2004 Location: O-town florida Posts: 3,203	Re: Milling YSR head i have a milled head on mine but i bought it pre-done. if you really want to wake the YSR up go with a pipe and carb

12-30-2009, 05:55 AM	#3 (permalink)
firepower354 Advertiser Join Date: Oct 2006 Location: Flint MI Posts: 14,206 My Mood:	Re: Milling YSR head .030 is safe, and adds a nice snap to the low end. __________________ Fire Power Minis, nuff said;) FirepowerMinis.com 810-237-9537 M-F 9-7 Eastern Time Zone 262-374-0706 Powder Coating Hotline Exclusive FPM parts and engines. Parts, installation and service for all makes. Honda Trail Bikes parts. Piranha & Medina bikes, thousands of parts, engines and accessories. Custom powder coating.

12-30-2009, 08:13 AM	#4 (permalink)
dixon PM Newbie Join Date: Apr 2009 Posts: 49	Re: Milling YSR head Thanks, 30 it is

01-06-2010, 05:53 PM	#5 (permalink)
johnson05 1st Gear Member Join Date: May 2009 Posts: 113	Re: Milling YSR head You should set the squish properly. Say .85mm to .90mm. Check it with solder to be sure. The problem with older bikes is previous owners might have milled the cylinder or head. Sometimes guys will mill a thou off the top and bottom of the cylinder along with the head just because the surfaces do not sit flush. My engine builder even likes to drill and put alignment dowels on the cylinder just to keep everything lined up a little better. A little bit of solder is cheap. If you shave too much off that ain't going to be cheap.

01-10-2010, 08:09 AM	#6 (permalink)
dixon PM Newbie Join Date: Apr 2009 Posts: 49	Re: Milling YSR head I was wondering about squish. How do I use the solder?

01-10-2010, 08:24 AM	#7 (permalink)
Kurlon 3rd Gear Member Join Date: Feb 2005 Location: Windham, ME Posts: 8,424	Re: Milling YSR head Basically, you assemble the motor with pieces of solder set around the edge of the piston, on the dome, etc. Turn the motor over a couple of times by hand and then pop the head off. Each piece of solder will be compressed from where it hit the head. Measure each piece, and note the thinnest you find. That measurement is what you use to determine your 'squish' value. Because you're using solder you can't use that measurement directly though. Solder is slightly elastic and 'springs back' when you take the pressure off it, so your actual squish value will be a touch less than the measured value. There are tables online that will convert from measured to actual squish based on the size and type of solder you use. You can also use clay/play-doh or get packs of wax strips made just for this purpose. The wax strips come in various colors, with the idea that you get the squish setting you want, and the next size up and down from that. When you test, you want to see the next size up squished, your target size just showing contact, and the undersized piece untouched.

01-10-2010, 09:52 AM	#8 (permalink)
firepower354 Advertiser Join Date: Oct 2006 Location: Flint MI Posts: 14,206 My Mood:	Re: Milling YSR head There's also rod elasticity, and multiple bearing clearances to take in account when the piston is rounding the top of the stroke. __________________ Fire Power Minis, nuff said;) FirepowerMinis.com 810-237-9537 M-F 9-7 Eastern Time Zone 262-374-0706 Powder Coating Hotline Exclusive FPM parts and engines. Parts, installation and service for all makes. Honda Trail Bikes parts. Piranha & Medina bikes, thousands of parts, engines and accessories. Custom powder coating.

01-11-2010, 05:14 PM	#9 (permalink)
dixon PM Newbie Join Date: Apr 2009 Posts: 49	Re: Milling YSR head Holly cow. I am original owner. Wish I could just take thirty thou off and call it a day.

01-11-2010, 07:54 PM	#10 (permalink)
firepower354 Advertiser Join Date: Oct 2006 Location: Flint MI Posts: 14,206 My Mood:	Re: Milling YSR head I'm sure you can. Yamaha was generous with clearance. Pull the head and base gaskets, bolt the jug & head on, and see if it hits. Work from there. __________________ Fire Power Minis, nuff said;) FirepowerMinis.com 810-237-9537 M-F 9-7 Eastern Time Zone 262-374-0706 Powder Coating Hotline Exclusive FPM parts and engines. Parts, installation and service for all makes. Honda Trail Bikes parts. Piranha & Medina bikes, thousands of parts, engines and accessories. Custom powder coating.

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