t500 top end ?

Tamadrmr26 · Post by **Tamadrmr26** » Fri Jun 24, 2011 10:26 am

before syncing my carbs on my 72 t500 i took it for a short ride around the neighborhood to warm it up a little. i noticed when accellerating the left side seemed to have a lot more sound coming out the exhaust. i checked by putting my hands behind the exhaust and i noticed at idle and when revving there was a lot more pressure on the left side. the bike didnt make it back. i also noticed some smoke coming out of the header/muffler seal on the right side. this leak could have leaned out the mixture and fried the rings correct? i pulled off the head and jug and the head gasket looks great, the cylinder looks good and still has good crosshatching. the piston looks a little rough on the top, maybe the previous owner started it up with some rust in the tank? i cleaned the whole fuel system when i got it before firing it up. so all this makes me think rings. how can i confirm that that's the problem?
thanks, Erik

tz375 · Post by **tz375** » Fri Jun 24, 2011 4:14 pm

That piston looks like new. I'm not so sure about that brown stuff on top but wipe it clean, check the rings are OK and put it back together.

On second thoughts, check the piston to bore clearance to be usre it's within spec and someone didn't bore or hone it too large.

titan performance · Post by **titan performance** » Sat Jun 25, 2011 9:23 am

Hi Tamad.......was the bike running on both cylinders?

That left hand piston looks to be the wrong way round to me. The arrow on top should be pointing forwards towards the front of the bike ! If the piston is fitted backwards, that cylinder wont have been firing.

From what I can see, the piston looks to be in good condition.

Put the piston back in the right way round, reassemble, and test ride. Hang on, because it will then be a 500 twin not a 250 single !

tz375 · Post by **tz375** » Sat Jun 25, 2011 11:36 am

Good catch. I looked at the piston and ignored the background.

I certainly won't match the transfer ports very well that way around....

Tamadrmr26 · Post by **Tamadrmr26** » Sat Jun 25, 2011 12:40 pm

the right hand piston is the same way. arrow towards the back of the bike. so that doesnt explain why it would run on one cylinder, or why it ran for a couple days and then died. i thought it was wierd that the arrow faced backwards because any of the dirtbike engines ive rebuilt the arrow always faced forward. so the arrow definitly goes forward?

Tamadrmr26 · Post by **Tamadrmr26** » Sat Jun 25, 2011 1:42 pm

flipped the pistons around. now the notches in the piston skirts will line up with the intake and exhaust ports. this is how it should be?

tz375 · Post by **tz375** » Sat Jun 25, 2011 3:22 pm

That's much better.

You are right. It doesn't explain the symptoms you described but it needed to be fixed, and now it's done. Now you can make sure that the top end is perfect and start from there

Tamadrmr26 · Post by **Tamadrmr26** » Sat Jun 25, 2011 3:56 pm

haha, i never would have thought the pistons were in backwards. that blows my mind that someone could've put them in like that even when there are arrows stamped on the top. i guess i'll reassemble and see what happens.

titan performance · Post by **titan performance** » Sat Jun 25, 2011 4:16 pm

When you posted the picture of the left piston in backwards, I assumed the right one was correct and the motor running on just the right side. But you're saying they were both incorrect?

STRANGE !

I don't think the motor can run in that state......

Tamadrmr26 · Post by **Tamadrmr26** » Sat Jun 25, 2011 4:34 pm

that's what i'm thinking. im really confused now and not quite sure what to do next. can you confirm that the notches in the piston skirts should line up with the intake and exhaust ports? and not the other ports that seem to connect to the bottom end of the motor(sorry, im new to these engines and don't know a lot of the proper terms)? i guess i will put everything back together and see what happens. i am going to completely tear the bike down to do a custom build but i want to get it running well before i dive into that.

tz375 · Post by **tz375** » Sat Jun 25, 2011 5:14 pm

Those appear to be correct now. The cutaways in the skirt match the transfer ports in the crankcases and in the lower part of the barrels.

Tamadrmr26 · Post by **Tamadrmr26** » Sat Jun 25, 2011 5:20 pm

ok. makes sense. i just wanted to be sure. thanks

Tamadrmr26 · Post by **Tamadrmr26** » Sun Jun 26, 2011 11:24 am

ok. i am going to order new rings and inspect the cylinder for scoring as well as check the bores. hopefully i'll have it running again in a week or 2. thanks for the help

titan performance · Post by **titan performance** » Sun Jun 26, 2011 1:46 pm

That's great news Tamad, I'm looking forward to reading your report once the motor is assembled correctly.
I bought a T500 way back in 81/82 that had been rebuilt, but the guy couldn't get it to run at all following the rebuild. I gave £100 for the bike, which was cheap even then, and found the pistons were exactly like yours.....backwards. However, that bike would not run, or fire at all, not even a glimmer ! Which is why I was surprised your bike had been running.

Still, that's the value of the forum......problem solved !

Tamadrmr26 · Post by **Tamadrmr26** » Mon Jun 27, 2011 4:50 pm

o wow. that's not what i want to hear haha. also, i should specify that my bike was manufactured in december of 1972, so i guess it is actually a '73. Not that i think that would make a difference in the pistons but i figured i should make that known. So i guess the obvious next step would be to get the correct pistons and rings. are the pistons still available anywhere?

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