Top end tear down. Curious to know.

Rickrod

What you have been finding?
What parts were worn?
Why the tear down?
What mileage?

Thanks in advance
Rick Smile

xs1961

Nowt
None
Curiosity or base-gasket leak!
Every 18 months/1500miles

xsleo

I tore mine down because of excessive oil use. 150 miles to a quart. Worn out pistons, rings, cylinders. Valves seals shot. Milage unknown. The speedo was changed. It said 1236 miles when I got it, tore it down at about 7000. Got over 11,000 on it how, runs great, and the oil stays in the engine. Loses/ uses maybe a few ounces in 2000 miles.

Rickrod

Hey Leo:
Thaknks for the reply.
Did you know the compression before the tear down?
Did you measure the bores and check the end gap of the rings?
Thanks again
Rick

jscribner · Full Member Joined: Aug 20, 2009 Posts: 11

My '80 Special was a barn bike found on e-Bay with about 9K on the odometer. I rode it for a summer (ran great), and then tore into it for a 750 Big Bore kit from MikesXS. I found at 14.5K miles there was just a lot of carbon built up in the head and pistons and valve faces. Very little wear anywhere else. I'll probably hit 18K miles easy by the winter, and it still runs great as a daily rider and weekend trip bike.
John Scribner

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

nj1639

My bike was an eBay pig in the poke, 15 k mi. Got it home and did a compression test 'cause it wouldn't run ("carbs need cleaning" bs ). Found 30 lbs comp in the right cylinder. A tablespoon of oil poured into the stripped plug hole (yeppers!)would bring it up to 130 lbs.
Found there was a ring in the cylinder wall, possibly from sitting outside in the weather on the side stand, allowing rain to get into the cylinder through the stripped plug hole, laying around the top ring and rusting the cylinder wall. I dunno, sounds logical.
I found a retired machinist that miked the cylinder for me and decided a 2 over bore would do the trick, so I ordered the pistons, rings and cam chain and had him do the bore after the pistons came in. Had the valve seals replaced at the same time. I put it all back together and we're doing fine.
I've been into the top end a couple times since for various upgrades and changes and the great mystery of it is no more. (Gets easier each time.)

xsleo

It was awhile ago, but as I remember one side was 125, the other 105. A squirt or three of oil helped a bit.
Piston to bore clearance was about .003. Ring end gaps were about .022 on one side .024 the other. Taper was under .002.
After a first over rebore, valves lapped, new valve seals and all new gaskets and seal for the rest of the engine and the old girl is doing great.
I did get in a bit of a rush and couldn't wait to get the new guide and cam chain. I just replaced them two weekends ago. The chain was so worn that the adjuster was hitting the cylinders in the chain tunnel as it boggled in and out. Made a lot of noise, real quite now.
The crank and rods were worn a bit but still usable.
I did some clean up on the head, just to smooth up the casting marks.
Elephant foot adjusters for the rockers arms. Stockers were pitted. The valve tips looked good, just some very minor pitting, you could see it, but couldn't feel it with a fingernail. Much quieter than the stock adjusters.
That's about it for the inside stuff. I did a few mods to the charging system and the ignition, lighting. Just finished the external oil filter and oil cooler mods. I hooked in a temp gauge in the oil lines to get a reading of how much effect each mod had on oil temp.
With the stock oil system it ran about 200 degrees on a 72 to 75 degree day. I did a 60 mile loop with each set up.
With the external oil filter the temps dropped about 5 degrees. I had thought it would be more. Cylinder temps dropped about 15 degrees.
Added the cooler in and the oil temps dropped to about 150 degrees, cylinder temps dropped another 20 degrees.
With everything in line oil temp was about 150 with cylinder temps about 235.
As things got cooler the difference between the cylinders got less. 235 and 237, the left a bit warmer.
I am very pleased with the results.

xsjohn

72-75 degree day my cylinders are about 215 degrees............the wind vanes I put on seem to work good too......oil coolers really don't effect cylinder temperatures.........and dimpling the pistons and smoothing the edges of the rings seem to add longevity since I am still in speck at 74 thousand........changed the rings at 20 thousand but now I consider that frivilous....... the 8-1 makes the engine run perfect........... bit of high end loss but nothing I miss......low end just purrs......just about no vibes at 65 on the express........oh 50K ago when I put in the new DID chain I smoothed the outer surface........should save the guides........when I raised the head 45 thousands last year the chain returned to original adjustment......

xsjohn

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

xsjohn

You guys might need 2 of them if you keep putting them together stock so they can beat themselves to death and run hotter than an oven and and have to rebuild at 20k if that........... Laughing

xsjohn

highspeedhamish · Full Member Joined: Jun 25, 2009 Posts: 62

Xsjohn... how did you smooth out the cam chain ? (awesome idea btw) did you simply run it over a belt sander?

xsjohn

No .........lay it out on a board.....320 paper on a block...don't have to go hog wild.....and don't forget the link......sand the link the same as the chain.......... and remove the sharp outer and inner edge of the chain face a bit that is caused by flattening the chain slightly.............I like talking about the inside of the engine.....

And the CR is a bit high for any usefull longivity and it causes a bunch of extra vibes and heat that tears everything up ...jaring the thing back a forth which also craps the chain and everything else.....my mikes DID chain has been in 50K now and I seldome adjust it........jaring causes all the F ups......smooth makes them last...........for sure......unless you are just lucky............

I wouldn't don't take the pistons out of the bore if the compression is good...like 150 or so...just causes more clearance with the new break in ....then you will need to fix it....get the carbon off and blow it off with air covering the rest....then raise the barrels and pull the pins and leave the pistons in the bore......

and if both cylinders because of the right cylinder running hotter aren't attended to with the "correct" mixtures....something is going to happen prematurely.......and white porcelain on an air cooled XS is not good ..... on either side.....and don't forget the timing....if it gets cranky at 2000 when you need it aroung a slow turn it is probably to advanced............

Then there is the gear ratio.......ratting it at 4500-5000 or more down the highway is going to trash it...... oiling the intakes.....another story there for sure

xsjohn

xsleo

If the oil cooler has no effect on cylinder temps , why did my cylinder temps drop after plumbing in the oil cooler?
I have read a bit about what happens to the heat generated by the burning of gas inside of the cylinder. Most goes out the exhaust, about 70%. The rest is about evenly split between the cooling system, fins on the cylinders and head. The rest is removed by the oil.
The fins on the cylinders and head cool the head, valves,cam, and the top of the piston.
The heat from bottom of the piston ,the rods, crank, are all cooled by the oil.
Oil can't handle high heat levels. If the oil temp gets above about 225 It starts to break down. If you can keep you oil below 200 It will last a lot longer. As will the engine. If your oil runs about 225 your engine may last 25,000 miles. If you can drop the temp to 210 the engine may go 50,000 miles. If you can get it below 180 the engine may go 100,000 miles.
If you can keep the oil cool it can do a better job of lubrication, and cooling.
We all understand what too much heat does for an engine. Adjusting the carbs to keep the burn temps inline is one way to help the heat problem.
Adding the fins to direct more air around the cylinders is a good way too.
I had the cooler and it wasn't hard to modify a side cover to hook it in. I also thought that adding a better filter would help keep the smaller stuff out of the engine.
I may try the fins as well. It won't hurt.
I would like to be able to hook in some sort of temp gauge to watch the cylinder temps, the infared thermometer is a good tool, but how much does the temp change by the time you slow to a stop. Get your thermometer out and check the temps.
I found that the oil temps can vary alot from 60 mph to a stop. The temp at 60 with the stock system would drop from around 200 to about 185 by the time you get stopped, then would start climing back up to around 195 after a minute or so. Even as you are riding the temps vary 5 to 10 degrees depending on speed, accellerating, or coasting.
At 60 the temp might be 180, accellerate to 70 the temps climb as you accellerate, then level off as you reach 70, maybe 195. Pick it up to 85 the temp can go up to around 210. Back it back to 55 the temps drop to maybe 165 as you coast down then climb back to around 175 when you hold the steady 55.
I can assume the cylinder temps can vary in the same way.
If I could hook a thermometer onto the engine fins to moniter the temp as I ride it would give us some more direct information on the temps under various conditions.
I found the oil temps and how they reacted to different conditions interesting. I would find the cylinder and head temps just as interesting.

pumps

"If I could hook a thermometer onto the engine fins to moniter the temp as I ride it would give us some more direct information on the temps under various conditions. "

I bet I could clip a temp probe from my volt meter to a fin to check that...if the bike was together!

xsleo

I'm sure their is a way to do it. I will do some research on it.

xsjohn

Well you guys are finally paying attention to cylinder temps.......finally got everything together correct with the 8-1 CR and the air fins......... and whether you like the idea or not the right cylinder has to be compensated for......... keep plugging and it will come together........... it's a combination of things that make it work right.....timing ...carbs and compression.... just turned 74 thousand..... original bore and pistons.........live and learn.......... pulls 18/29 down the express like a dream.....very little vibes....no heat.........slick.....

Couple of or more other things too..........but I would be wasting my breath///////.....40 years of background on these Yamahas....what would I know........... Laughing

xsjohn

highspeedhamish · Full Member Joined: Jun 25, 2009 Posts: 62

Hey Xsjohn...

Just read a quick blip about a Honda (I think the VFR for 2010) where they added more material to the crankshaft... to smooth it out. Much like your earlier theory of doing the same. Just fyi...

xsjohn

The Japs liked to lessen the spinning weight to increase acceleration and HP...... that theory worked but didn't smooth out the ride back then....... like taking off the big flywheel of a 71 360 enduro and putting on the tiny cdi flywheel........faster but definitely not smoother........ been there and done that..... somehow they overcame that problem on the new sport bikes.....but I can't afford them.......... nor do I want to go that fast....... don't think today on my 170 mile jaunt did I go much over 70 mph.......or 3700 rpm..... chicken in my old age I guess...... but enjoyed every minute of it.....especially after I stopped for a couple of beers halfway...... Laughing

xsjohn

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