Questions about rebuilding top end - Motorcycle-Journal Forums

bigE · 05-23-2005, 12:13 AM

HI guys. I finally had some time to work on my old 1986 RM250. I was having major performance issues (see Crappily Running RM250 ). Ive pulled the top end off and my piston is scorched. The sleeve inside the cylinder appears to be in good shape. There is no burn or scratch marks. My question is: Is there any way to tell what size piston i have without using complicated and expensive measuring tools that i dont have? There is a bunch of letters on various parts of the piston but i dont know what they all mean.... Also, are sleeves easy to install? Im thinking of replacing it too if its not too expensive and/or difficult to do... This is my first time doing top end work so any advice would be appreciated

Dave2122 · 05-23-2005, 11:01 AM

You should have a machine shop take measurments of the cylinder bore and see where it is at with the tolerences. You may only need to hone it out and install a new piston and rings. On your piston crown you should have some numbers(example 0.30 which is 30 over) If you do not have any numbers you most liekly have a standard piston. Once you get the bore measured you can either install a new top end or if it is out of specification you will need to have it bored out to the next useable size by a machine shop. If it does require a bore job you need to make sure they relieve the exhaust bridge (the thin part of the cylinder bore thatruns between the exhuast ports) this needs to be done as that thin section heats up much faster and will cuase a siexure if not taken back a little with a dremel (do not do it yourself if you have never done it before) Boring usually costs about 40-60 dollars.

This is a list of parts you should change for a top end....

Head gasket
Base gasket
Piston
Rings
Roller bearing (for wrist pin)
Wrist Pin
C clips (for wrist pin)

Should tun about 130 dollars give or take.

Any questions feel free to ask me!

bigE · 05-26-2005, 12:36 AM

thanks dave! My buddy is going to take every thing to his school and measure it for me. On top of the piston it has a one, several spaces then 00 mm. It looks something like: 1 00 mm. Does this mean its bored 1mm over?

05-23-2005, 12:13 AM	#1 (permalink)
bigE Kickstand Operator Joined: Apr 2005 Bike: 2000 SV650 & 2000 Marauder Location: DFW, Texas Posts: 297	Questions about rebuilding top end HI guys. I finally had some time to work on my old 1986 RM250. I was having major performance issues (see Crappily Running RM250 ). Ive pulled the top end off and my piston is scorched. The sleeve inside the cylinder appears to be in good shape. There is no burn or scratch marks. My question is: Is there any way to tell what size piston i have without using complicated and expensive measuring tools that i dont have? There is a bunch of letters on various parts of the piston but i dont know what they all mean.... Also, are sleeves easy to install? Im thinking of replacing it too if its not too expensive and/or difficult to do... This is my first time doing top end work so any advice would be appreciated

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
rebuilding salvage katana 750 98	snakethis69	Katana Planet Emergency Shelter	0	03-18-2006 11:21 PM
Rebuilding 1976 RM250	oldfart1958	Mechanics Corner	7	08-29-2005 02:47 PM
What not do do When rebuilding brake calipers!!	TsPerformance	Tips & Training	9	12-09-2004 06:31 PM
DR 350 Questions	ElJefe	Dirt Bikes & ATV's	11	06-14-2004 10:14 PM
Anyone offer me an estimate for rebuilding an engine	FatRakoon	Mechanics Corner	2	04-13-2004 05:47 AM

05-23-2005, 11:01 AM	#2 (permalink)
Dave2122 Sprocket Pilot Joined: Sep 2004 Bike: Which one of the 9? Location: USA Posts: 887	You should have a machine shop take measurments of the cylinder bore and see where it is at with the tolerences. You may only need to hone it out and install a new piston and rings. On your piston crown you should have some numbers(example 0.30 which is 30 over) If you do not have any numbers you most liekly have a standard piston. Once you get the bore measured you can either install a new top end or if it is out of specification you will need to have it bored out to the next useable size by a machine shop. If it does require a bore job you need to make sure they relieve the exhaust bridge (the thin part of the cylinder bore thatruns between the exhuast ports) this needs to be done as that thin section heats up much faster and will cuase a siexure if not taken back a little with a dremel (do not do it yourself if you have never done it before) Boring usually costs about 40-60 dollars. This is a list of parts you should change for a top end.... Head gasket Base gasket Piston Rings Roller bearing (for wrist pin) Wrist Pin C clips (for wrist pin) Should tun about 130 dollars give or take. Any questions feel free to ask me!

05-26-2005, 12:36 AM	#3 (permalink)
bigE Kickstand Operator Joined: Apr 2005 Bike: 2000 SV650 & 2000 Marauder Location: DFW, Texas Posts: 297	thanks dave! My buddy is going to take every thing to his school and measure it for me. On top of the piston it has a one, several spaces then 00 mm. It looks something like: 1 00 mm. Does this mean its bored 1mm over?

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)