Head issue?

xs650hacker · Feb 25, 2011

Ok, new to the forum but have gleaned tons of excellent info so far. I recently picked up a 78 XS650 SE for $100, mostly complete and supposedly running (never fired it up due to winter setting in) and decided to rebuild the top half of the motor while waiting for my hardtail to arrive and it's winter anyway. Plus I get to use the unused front bedroom as the new shop. Nothing like building a chopper in the front room of your trailer!

On to the issues, there was a ton of carbon on the pistons and around the valves, which as you can see by the photos, I have begun to clean up. Not a fun task, but being it's winter, what better to do. Pistons are now clean, little to no movement in the piston and no scoring in the cylinder wall.

I was going to attack the head next and noticed a piece of metal missing (shown by the arrow in the picture), how critical is this? Am I going to be able to use this head as is or need to get it fixed or just buy a new head? Also, since this is my first rebuild, are those valves going to clean up or should I just replace them?

I haven't noticed any other problems with the motor, cam chain looks new, all the plastic is still on the guide and I believe it only had 6000 miles on the odometer when I disassembled the bike and brought it inside. Motor was covered in mud like maybe this was used mainly on or around the farms up here, the main reason (that and to get to know the motor better) for the rebuild.

Any other pics of the motor or improvised shop ya want to see let me know and I'll upload them.

retiredgentleman · Feb 25, 2011

I believe you will be able to re-build that engine. The missing metal should not be a problem. Take everything apart.............valves, valve seals, valve springs, pistons , rings etc...............compare to the specs that are in the service manual for the 78SE (available at www.biker.net). Use micrometers, feeler gauges, dial indicator etc.

Valves will clean up, but they will certainly need to be reground. Piston to cylinder clearance is important.............go by the specs. You will want new rings, new valve seals. If only 6000 miles, then front cam guide and cam chain may be OK to reuse. Buy a gasket kit and oil seal kit.

xs650hacker · Feb 25, 2011

Thanks retiredgentleman!!

I've got a Haynes and a Clymers and the service manual from biker.net. I'm glad that missing metal shouldn't cause a problem. Time to move forward and break out the micrometer, hopefully I don't encounter any more problems.

CDNTX650 · Feb 25, 2011

Clean the combustion chambers up and see if it will hold gas in them for a few days with the head upside down. My motor had around that for miles and i never did any valve work to it. Has great compression and runs like a top now. (all i did was hone, rings and stem seals and only reason it was apart was because of the stem seals, it ran great but smoked like crazy.)

xs650hacker · Feb 25, 2011

CDNTX650: It will hold gas in there for days on end, I did that first because I didn't want to mess with removing valves, springs, etc. (I'm new to this motor and nervous to make an extremely expensive mistake) but looking on this forum I think maybe it best if I just pull it all apart and attempt to clean and/or replace?

Update: Pulled the cylinder off so pistons are exposed, cylinder walls look good to me, no obvious scoring and I feel nothing while examining with my hands. Should have did this in the first place, would've been much easier to clean that darn carbon off!

TwoJugs · Feb 25, 2011

If you feel bored you might want to replace the valve seals. They are cheap and easy to do IF you have a valve spring compressor. The rest of the pix look good. Did I see broken fins on the cylinders?.

xs650hacker · Feb 25, 2011

TwoJugs: I'm going to make a valve spring compressor from a 6" deep throat C clamp I have. The cylinders fins are all there but there are two small chunks taken out of the 6th fin down, nothing major I believe.

Ok I have broke out the micrometer and the haynes manual says the cylinder barrel should be between 75.00-75.02 mm. Mine reads at 75.00 so I feel good about that. I'll order me a gasket set and new rings from MikesXS, finish cleaning the last little bit on the pistons and call that done for now and focus on the valves.

xscessivecompulsive · Feb 26, 2011

Hey, where in South Dakota are you from??

XsC

hooktool · Feb 26, 2011

I doubt you need to grind the valves unless there's a problem. Usually a quick lapping will do it.

John

tx650 · Feb 26, 2011

xs650hacker said:
Ok, new to the forum but have gleaned tons of excellent info so far. I recently picked up a 78 XS650 SE for $100, mostly complete and supposedly running (never fired it up due to winter setting in) and decided to rebuild the top half of the motor while waiting for my hardtail to arrive and it's winter anyway. Plus I get to use the unused front bedroom as the new shop. Nothing like building a chopper in the front room of your trailer!

On to the issues, there was a ton of carbon on the pistons and around the valves, which as you can see by the photos, I have begun to clean up. Not a fun task, but being it's winter, what better to do. Pistons are now clean, little to no movement in the piston and no scoring in the cylinder wall.

I was going to attack the head next and noticed a piece of metal missing (shown by the arrow in the picture), how critical is this? Am I going to be able to use this head as is or need to get it fixed or just buy a new head? Also, since this is my first rebuild, are those valves going to clean up or should I just replace them?

I haven't noticed any other problems with the motor, cam chain looks new, all the plastic is still on the guide and I believe it only had 6000 miles on the odometer when I disassembled the bike and brought it inside. Motor was covered in mud like maybe this was used mainly on or around the farms up here, the main reason (that and to get to know the motor better) for the rebuild.

Any other pics of the motor or improvised shop ya want to see let me know and I'll upload them.

If you have gone this far then you may as well pull the valves out to check the tollerances,it's not a drama.A machine shop in the area will bring it up to spick and it will also give you peace of mind knowing the head is ok.If the clearances are ok then you can lap and clean the valves up yourself.Sometimes it don't pay to take short cuts,but then you are the only one you have to satisfy.Take Care.

xschris · Feb 27, 2011

tx650 said:
If you have gone this far then you may as well pull the valves out to check the tollerances,it's not a drama.A machine shop in the area will bring it up to spick and it will also give you peace of mind knowing the head is ok.If the clearances are ok then you can lap and clean the valves up yourself.Sometimes it don't pay to take short cuts,but then you are the only one you have to satisfy.Take Care.

x2

xs650hacker · Feb 27, 2011

xscessivecompulsive: I live in Aberdeen, not originally from here though (New Jersey) but it's alright with Sturgis a few hours away.

I made a spring compressor from an 8" deep throat clamp and a piece of pvc that I notched out and am in the process of cleaning the valves. I totally agree with both previous posts that yes, I have gone this far and might as well do the job right for piece of mind knowing that all is back to original again.

With the repair manuals and the forum, tearing this motor apart is rather easy and I labeled, bagged and photographed everything during disassembly so shouldn't have too many problems putting it all back together.

Head issue?

xs650hacker

XS650 Member

Attachments

retiredgentleman

XS650 Guru

xs650hacker

XS650 Member

CDNTX650

XS650 Guru

xs650hacker

XS650 Member

TwoJugs

Excess XS

xs650hacker

XS650 Member

xscessivecompulsive

Live 2 Ride, Ride 2 Live

hooktool

XS650 Junkie

tx650

XS650 Enthusiast

xschris

from earth

xs650hacker

XS650 Member

Similar threads