Vintage Dirt Bike Q & A

I was riding my 1974 Yamaha DT 360 today when it got really loud. I stopped and noticed the factory compression release that mounts into the cylinder above the exhaust port was missing. I looked everywhere but could not find it. I never used it and did not even have a cable. I am wanting to just plug the hole in the cylinder if possible. Does anyone know the thread size. Any other suggestions are appreciated.

might try taking the lower portion of the valve then remove the plunger then weld the hole shut.that is the only idea i have there.

when i speak of plunger i am talking about the valve itself.here is a pic of what i am speaking of.i have the valve open in this pic remove that piece and weld the hole shut on it then reinstall it on the engine.

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(2) 1968 DT1 1970 RT1M,1970 DT1C 1971 RT1B Enduro 1974 MT250 1974 DT250A (2) 1975 DT400B 1974 DT100,1978 DT175
1975 CR250M1 1979 CR250R 1979 Kawasaki KZ400H1 Jesus is Lord!!

Good idea but I'm missing that whole thing! It fell out going down the road. How the bike could still run is beyond me but it did.
I found one on ebay for a buy it now of $25 plus $8 shipping, so $32 total. I thought that was bit high and wanted to pay more like $20 total. I emailed the seller and offered him $25 shipped, he came back with $30 shipped so I passed.
I did some more ebay searching and found one for a 1976 DT400 for $15 plus $5 shipping, right in my price range! I looked up the part number for a 1976 DT400 and a 1974 DT360 and they were the same so I hit the buy it now and it came in the mail yesterday. Looks good but I have not installed it yet.

is the threads intact in the cylinder or is the bung (threaded portion) broken off in the cylinder? if the threads are still in the cylinder you can install another unit and be on the way.i think only the 74-76 DT360 and 400 will fit,the RT1 from 1971 and the 72-73 RT2 and RT3 360 compression release while looking similar will not fit because the threaded portion is smaller in diameter than the 74-76 parts.

to install the replacement one you should remove the head to be able to tighten it as the nut portion is covered by the head when threaded in and will make it much more difficult if not impossible to tighten it properly.

the hole for the compression release in the cylinder wall is a small hole about 1/8" or smaller so it will still run but it will not run very good and it will sound bad as it runs because of the small air leak and exhaust leak that it forms,it is similar to it being ran without a pipe to a lesser degree.

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(2) 1968 DT1 1970 RT1M,1970 DT1C 1971 RT1B Enduro 1974 MT250 1974 DT250A (2) 1975 DT400B 1974 DT100,1978 DT175
1975 CR250M1 1979 CR250R 1979 Kawasaki KZ400H1 Jesus is Lord!!

If memory serves me well, the threads are the same as b8e series spark plug. You can either stick a plug in it, or weld up the hole in an automotive spark plug non-fouler and use that, or find one of those plugs that goes in the second spark plug hole of bikes of that era.

The compression release on my 360 is hooked up and functional though. I sure like that thing. It kicks through like a worn out 125 and fires first kick nearly every time.

I have already installed my ebay compression release. The threads in the head looked great. I did not pull the head to install. I just took the compession release apart, tightened it with a socket then reassembled the front portion of the release.
The bike was already stripped down and had an MX360 gas tank on it when I got. I ordered all new MX360 plastic from DC plastics. I still need a silencer yet, its missing. I'll probably just make what ever I can find work but I can't find anything cheap.

sounds like you got it lined out!

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(2) 1968 DT1 1970 RT1M,1970 DT1C 1971 RT1B Enduro 1974 MT250 1974 DT250A (2) 1975 DT400B 1974 DT100,1978 DT175
1975 CR250M1 1979 CR250R 1979 Kawasaki KZ400H1 Jesus is Lord!!