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Old 12-26-2017, 08:14 PM   #1
jdsmetx
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Default MX360 Questions

I have been slowly putting together my 74 MX360 basket case and currently working on the engine. I had my local vintage shop bore my cylinder and provide me a Yamaha piston and ring which they purchased from ebay. During assembly, I noticed the ring was bent and out of round. I did my best to bend it back into shape but was not very happy with the way it fit on the piston.
Question: Should I use this ring or purchase another?

The other issue is I sent my cylinder head and a bunch of other parts to be vapor blasted but the cylinder head was lost! Now I need another cylinder head for a 74 MX360. I have a DT360 cylinder head but not sure what the difference is.
Question: Can I use the 74 DT360 cylinder head and what can I expect in performance?

Lastly, I have the stock ignition for this bike but I suspect its bad. I seen a new CDI box from www.CDIBOX.com and wonder if anybody has used these. The information on their website says they fixed the "kick back" problem from back in the day and it's a "plug and play" setup.
Question: Anybody use these or is there something else such as PVL Ignition?

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Old 12-26-2017, 09:51 PM   #2
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Default

Quote:
Originally Posted by jdsmetx View Post
I have been slowly putting together my 74 MX360 basket case and currently working on the engine. I had my local vintage shop bore my cylinder and provide me a Yamaha piston and ring which they purchased from ebay. During assembly, I noticed the ring was bent and out of round. I did my best to bend it back into shape but was not very happy with the way it fit on the piston.
Question: Should I use this ring or purchase another?

The other issue is I sent my cylinder head and a bunch of other parts to be vapor blasted but the cylinder head was lost! Now I need another cylinder head for a 74 MX360. I have a DT360 cylinder head but not sure what the difference is.
Question: Can I use the 74 DT360 cylinder head and what can I expect in performance?

Lastly, I have the stock ignition for this bike but I suspect its bad. I seen a new CDI box from www.CDIBOX.com and wonder if anybody has used these. The information on their website says they fixed the "kick back" problem from back in the day and it's a "plug and play" setup.
Question: Anybody use these or is there something else such as PVL Ignition?

I'll answer your first question . . .
Toss the ring in question . . . any unnecessary bending will compromise it's strength, and make it more susceptible to breakage while running. Also, a ring must be perfectly true and flat to seal . . . any bending (other then what's required to get it onto the piston) will likely warp it permanently and end up causing blow-by.

IMHO, . . . it's not worth the risks, just to save a few bucks.

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Old 12-27-2017, 07:25 AM   #3
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Quote:
Originally Posted by Enduronut View Post
I'll answer your first question . . .
Toss the ring in question . . . any unnecessary bending will compromise it's strength, and make it more susceptible to breakage while running. Also, a ring must be perfectly true and flat to seal . . . any bending (other then what's required to get it onto the piston) will likely warp it permanently and end up causing blow-by.

IMHO, . . . it's not worth the risks, just to save a few bucks.

.
Thanks Enduronut! Just ordered another from evil bay!
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Old 12-27-2017, 06:34 PM   #4
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A PVL ignition as far as I know is a self contained unit and eliminates all the stock ignition.

I had good luck putting a 77-79 YZ400 ignition on a friends MX360 when I went through it (lost my ass on that deal) for him 2 years ago. The stator plate, flywheel and box. All of that a direct bolt on and even the timing marks lined up. All that is needed is the correct flywheel nut, lock washer and flat washer from the donor bike or new available from Yamaha replacing the nut for the stock internal rotor.

For sure that (78 I used) ignition calmed down the power delivery making it more ride-able.

I'm not gonna lie, I am not a fan of those bikes. The airbox is absolute junk. Handles like a worn out bread truck. The front will wash out on the driveway pushing it out to the trailer. Will put you in the hospital if you try to go fast on it.

Better suited as a shrimp boat anchor. Just saying. Good luck with that.
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Old 12-27-2017, 07:00 PM   #5
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Another thing to be aware of is the very fragile 1st gear on the main shaft. The teeth will shread right off that shaft and be floating around in your gear box. The stock gearing ratio pretty much requires the use of 1st gear when riding. Whatever it takes you need to final drive gear the bike so you don't need first gear for anything more than riding in the pits.
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Old 12-27-2017, 07:32 PM   #6
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Quote:
Originally Posted by UTBMXCruiser View Post
Another thing to be aware of is the very fragile 1st gear on the main shaft. The teeth will shread right off that shaft and be floating around in your gear box. The stock gearing ratio pretty much requires the use of 1st gear when riding. Whatever it takes you need to final drive gear the bike so you don't need first gear for anything more than riding in the pits.
Thanks for the advice on the ignition, I'll look into it. When I got this bike it was in boxes and the cases were already apart. When I started putting it back together 1st and 3rd gear were toast probably from what you described. I have the engine back together (at least the bottom end) and everything seems to be coming together....we shall see...lol!
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Old 01-23-2018, 08:08 PM   #7
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Default gasket

So I got the engine assembled and started a leak down test. As I suspected the intake manifold leaks which is a easy fix but the base gasket on the cylinder is leaking. I torqued the cylinder bolts to ~30 ft-lb as described in my manuals but is that tight enough? Head gasket is holding along with spark pugs. Good news is the crank seals are good!!! I was really sweating that but all is good there.
What can I do to the base gasket? I had a local guy do the bore and provide me the piston, ring, base gasket and head gasket. The base gasket looks like it was custom made but looks very close to original. Its green type material also this is the same material used for the intake manifold.
Any suggestions would be greatly appreciated!!
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Old 03-13-2018, 11:42 AM   #8
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Cometic has the gaskets.
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Old 03-15-2018, 08:31 PM   #9
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Default Mx360

I restoredamx360 and 400 using a 1979 yz400 ignition, worked great. the DT360 has smaller porting. That means good low end torque but the top end torque kinda peters out. I think I have a MX360 jug in your intrested. I'm sure it would need cleaned up.
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Old 03-16-2018, 08:44 AM   #10
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Default gasket & ignition

Thanks for the information. I bought gaskets from gasket king but have not had the opportunity to change them out. I also decided to purchase a cdi box from www.CDIBOX.com. This seems to me the best route for my project and the yz400 ignition seems to be as elusive as the NOS MX360 cdi unit. Could be I am not looking in the right places.
The cylinder head is what I need. My DT360 head is visibly smaller meaning the fins are shorter and the front does not meet the diameter of the cylinder. I'm guessing the larger fins of the MX head are for heat dissipation. I found a NOS head on evil bay but a bit pricey. I also looked at a used head but the time I get it machined would be the same price as the NOS....

Good news I got the new tires mounted on the rims and look good. Slowly making progress!
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