Need help with 1983 Yamaha tri moto yt175j

[Madmike420]

That's all for now till I get home

Sent from my LM-X510WM using Tapatalk

[stoshu]

If you are ready to do it right this time, you can use that new piston as an ashtray. Pull the engine out, remove the cylinder and take it all to Ray at Associated Crankshaft. He is just North of Winnipeg and does rebores for most dealers in town. He can get the piston you need and bore your cylinder to the proper size. You could also try Gord at Main Motorsports, but be prepared to leave him a deposit for the work you need done if he doesn't know you. Way to many customers drop stuff off and then cant/won't pay the bill.

[fabiodriven]

I agree with stoshu unless you have the means to measure and hone that cylinder correctly, assuming it doesn't wind up needing a bore. The only way you'll be able to mic the entire jug is with ID snap gauges. I'm going to go ahead and guess this might all be a bit more than you're capable of handling at home.

[Madmike420]

About how much does that cost ?

Sent from my LM-X510WM using Tapatalk

[stoshu]

Probably $60 for a bore, plus piston, plus gaskets.

[Madmike420]

The new piston .

Sent from my LM-X510WM using Tapatalk

[Madmike420]

No good?

Sent from my LM-X510WM using Tapatalk

[fabiodriven]

Pictures do help sometimes but what you have to do is actually find out what numbers you need.

Find out what piston size you have, then find out what bore size that piston requires. WRITE THOSE DOWN

Bore needs to be measured in multiple places, not just at the top and bottom. Measure the cylinder and get your numbers. WRITE THOSE DOWN

Compare the numbers of what cylinder size would be correct for your piston with the actual numbers you have measured your cylinder out to be. Assuming your bore is good and usable, and it measures within spec for the piston you have there, then hone it.

Look up the numbers for what your ring end gap should be. WRITE THAT DOWN

Take your rings and use the piston to slide them gently into your bore. Then measure your ring end gap. WRITE THAT DOWN

Then compare those two numbers and see if your rings are within spec.

Your piston rings can most likely only be installed one way. If your rings are directional, be sure you do not put them in upside-down.

You have some tools there, you can do some stuff. Don't expect this machine to run right if you cut corners and don't bother concerning yourself with "why it won't run right with the wrong piston". It won't run right with the wrong piston because it's the wrong piston, what more do you want to know? Fix it and you'll find out why.

[fabiodriven]

And as I said, measure your piston clearance as well.

[ironchop]

Ok Mike...

So you know pistons are made tapered, right? The skirt will be the widest part of the piston because the skirt is what stabilizes the piston in the cylinder bore. You ALWAYS measure piston-to-cylinder clearance at the skirt and feeler guages are not a good way to measure it. Feelers will contact at the edges of the feeler instead of the center where the radius of the cylinder wall will be farthest from the piston skirt. I use a guage pin set. Most guys don't have that kind of metrology equipment laying around which is why most guys just outsource the bore job to a shop with the correct measuring equipment. Sometimes a used cylinder will be tapered or out-of-round, so just honing won't cut it. You must measure the cylinder at several points inside to get an accurate idea

You MUST have the new piston present in order to bore the cylinder to fit the piston, not the other way around.

In your case, the calipers are good enough for me to say that I can tell you that your piston skirt looks to be almost 1mm too small for that bore (0.0393 inches is definitely too much clearance)

Sent from my Z958 using Tapatalk

[ironchop]

Just to add to what I said above

What happens with a piston too small, is that the piston will tilt in the bore. Upstroke will tilt the piston one direction, and the downstroke will make it tilt the other way.

When the rings aren't square to the bore (as in the case of a tilted piston), they won't seal correctly and will leak compression. The more they tilt, the bigger the leak. The piston skirt is meant to help keep the piston straight and the rings square to the bore

Sent from my Z958 using Tapatalk

[Madmike420]

Yea it leans that's what caught my attention. Pretty sure it's to late for that piston cuz there r marks on it now. My crankcase doesn't line up properly. I'm gonna try get a pic where u can see it.

Sent from my LM-X510WM using Tapatalk

[Madmike420]

I'm starting to get really frustrated. I bought a harmonic puller to get the flywheel off so I can take the crankcase apart and see why it isn't lined up but it's not working the bolts that came r to big and my tap and die set isn't cooperating.

Sent from my LM-X510WM using Tapatalk

[Madmike420]

I know maybe I should get a bong and some weed and some BBQ chips I think someone said lol to help chill me out. I've spent hours and hours and hours working on this trike.

Sent from my LM-X510WM using Tapatalk

[ironchop]

Don't worry about that case mismatch inside there.

The only place it would matter is above where those two studs are coming out.... That's the deck where the cylinder mates to the cases and is where you should have no mismatch... on that deck and between the two studs where the case seam runs, the cases should be perfectly flush on that gasket surface

Sent from my Z958 using Tapatalk