Yamaha XT500

[2wheelsgone]

Hey guys I have a spare 77 TT motor that I am in the process of working on and I have a few questions. I took the top end off and found that I have a 92mm high domed piston. There are no markings on the piston. I looked at the rod and it has the #583 D stamped on one side and the word Yamaha on the other. The camshaft has the letter D stamped on it with no other markings.

1. Is this piston size used often and will it be reliable at this size.

2. Is this the stock TT rod and is it a good idea to stay stock with this size piston?

3. Is this the stock camshaft?

As you can see most of my question center around if this is a big bore piston, stock rod and camshaft, after I get the valves redone will this be a reliable setup for general dualsport Hooliganism?

Thanks for any help.

Steve

[Pablo83]

Originally Posted by pabloxt500

i guess i should have said they're the rear shocks. forks i've done, but not shocks.

Well if you want to do it yourself I'll tell you how. I don't know what your shock looks like so you'll need a digital camera.

If you want someone else to do it I'd recommend Davey Durelle, but his website seems to be messed up right now. Anyone have a phone number for Davey?

[Garthe]

---

Mats, thanks for the flashback...I was 18 years old when I bought the same bike brand new...the fun, the storys, suprized I lived through it.

Good luck with the rebuild. Jim

[Mats]

Thanks Jim!
Engine started up fine the other day but had no oil pressure. So I took off the clutch cover and filled the oil pump up and after that it regained pressure. It hasn't been started in nine years so I guess it was a bit dried out. Here's a before pic! I'll get back with an "after" pic soon I hope! /Mats

Attachment 221456

[mudmantra]

Originally Posted by 2wheelsgone

Hey guys I have a spare 77 TT motor that I am in the process of working on and I have a few questions. I took the top end off and found that I have a 92mm high domed piston. There are no markings on the piston. I looked at the rod and it has the #583 D stamped on one side and the word Yamaha on the other. The camshaft has the letter D stamped on it with no other markings.

1. Is this piston size used often and will it be reliable at this size.

2. Is this the stock TT rod and is it a good idea to stay stock with this size piston?

3. Is this the stock camshaft?

As you can see most of my question center around if this is a big bore piston, stock rod and camshaft, after I get the valves redone will this be a reliable setup for general dualsport Hooliganism?

Thanks for any help.

Steve

Interesting.. I just picked up a 77 xt500 with a 76/77 tech manual. I don't know if this adds up but 583- is the first numbers in the 1976 TT500 serial numbers. The 92 piston was used with the stroker crank in some motors to make 605cc's. So you could check the stroke and see if it's 84 or 91mm. Also if the piston is 92mm, I'm pretty sure it should have an oversized sleeve. Reliable? depends on what kind of shape the motors in and how hard you push it. I'd check your cam lift and install a good set of valve springs. all kinds of fun.

[2wheelsgone]

Thanks mudmantra. Can you give me a good idea how to measure the crank? I do not have the lower end taken apart. I will measure the lift on the cam as well. I bought this motor from a guy who said another guy used to ride it and outrun everyone on the dirttracks where they live. I have not been able to find the guy who actually rode it and had it built to question him. I'm also having trouble finding a set of rings to fit the piston. When I said before that there were no markings on the piston that was not true. The words Forged True are on the under side. I since learned that they were a piston manufacturer, bought out by BME racing out of Nevada back in the early 80's. I have an email sent to them to see if they may have rings for it. I'm thinking it's going to be lot's of fun to ride! Its been alot of fun just working on it and thinking about riding it.

[mudmantra]

Originally Posted by 2wheelsgone

Thanks mudmantra. Can you give me a good idea how to measure the crank? I do not have the lower end taken apart. I will measure the lift on the cam as well. I bought this motor from a guy who said another guy used to ride it and outrun everyone on the dirttracks where they live. I have not been able to find the guy who actually rode it and had it built to question him. I'm also having trouble finding a set of rings to fit the piston. When I said before that there were no markings on the piston that was not true. The words Forged True are on the under side. I since learned that they were a piston manufacturer, bought out by BME racing out of Nevada back in the early 80's. I have an email sent to them to see if they may have rings for it. I'm thinking it's going to be lot's of fun to ride! Its been alot of fun just working on it and thinking about riding it.

to measure the stroke put the piston and cylinder back on with the head off. you really don't need to put the rings or clip back on because your only going to turn it once. measure from TDC to BDC, use a dial gauge or mark the cylinder and measure. 84mm is stock. just be careful with the cam chain when you turn it. Cam base is in. 32.8mm ex. 32.13mm . cam height in. 39.23mm ex. 39.25mm. stock. stock lift intake 7.23 mm exhaust 7.25 mm. I don't have the rocker ratio yet, so i don't know what the total lift is. more research. I dig these old motors.

[2wheelsgone]

Thanks. That will tell me alot more about this motor. I'll check it out after work this evening. These really are fun bikes to own and ride. I'm going to finish this motor and then put it in my XT to tune it up and get it running good. Then who knows what I will do after that. I may leave it in the XT or start with another frame and go from there.

[Mats]

Originally Posted by mudmantra

just be careful with the cam chain when you turn it.

I wasn't careful enough, so the cast in protrusion in the block that's used as a pointer when setting the timing
(missing at the arrow in pic), it broke off when I turned the engine over with too much slack in the cam chain.
I didn't notice it and only by luck did the broken off piece fall out before I put the cover back on.
It's still OK to set the timing by the piece left and I'm sooo happy I didn't find the piece by it jamming something in the engine while it was running!
Attachment 222029

[2wheelsgone]

Thanks guy's that is something to watch out for!

[mudmantra]

step 1 for me is to just get the old 77 xt500 running stock. I have the carburetor off. I'm cleaning it now, some of the junk in the carburetor will not clean out with carburetor cleaner. Air cleaner is junk, so I have a new one on order. Gas tank was rusted through, so I have a dented TT500 tank on the way. New petcock on order. Seat is ripped a bit, but I can use it for a ride or two and then get it recovered. I think I'll change the oil and filter before I start it. New spark plug too. Must have been years ago when this last ran.

[pabloxt500]

Originally Posted by grimmboy

I am the US supplier for Kedo parts and accessories.

can you get front brakes for the XT?

[Mats]

OK rebuild of the '81 XT is done! ...except for the silencer.. Those buggers are expensive!
Hope Santa brings one.
Attachment 222139

[pabloxt500]

Originally Posted by Mats

OK rebuild of the '81 XT is done! ...except for the silencer.. Those buggers are expensive!
Hope Santa brings one.
Attachment 222139

yeah, i keep seeing those go for big money on ebay.
all rusty and even missing the spark arrestor. crazy.
i got mine with my bike for almost the same money as the pipes are going for.

[Mats]

Originally Posted by pabloxt500

yeah, i keep seeing those go for big money on ebay.
all rusty and even missing the spark arrestor. crazy.
i got mine with my bike for almost the same money as the pipes are going for.

The bike had been under roof and a tarp, but on bare ground, for 8 years.
Lot of moisture captured under that tarp. So the silencer was like a biscuit. A very rusty one!
I'll get an after-market one. NOS are heavy and too dear.