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Makotosun

Rebuilding my Dt 360a motor

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Replied by treeves on topic Rebuilding my Dt 360a motor

I got my crank back from crankworks this week., to my untrained eyes I think they did a great job.  They fixed the pitting on the seal area on mag side, new rod, and rebuilt crank. Did take about 3 months to get crank back but all parts are in so will start putting back together this week. 
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20 Jun 2021 13:28 #11

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Replied by treeves on topic Rebuilding my Dt 360a motor

I have completely rebuilt my motor and have put 40 miles on the engine.  I have noticed the motor will hang for a second before idling and is worse when hot  I did pressure test and pumped the motor to 4 pounds, it took about 20 minutes for it to drop to 3 pounds. I do have a temp gauge and the hottest i have had was 350 degrees.  The motor is leaking some oil from either the exhaust or base gasket, I have checked base gasket with soapy water and I do not see a leak.  The only thing I have not checked is the crank seal, which are new.   
19 Jul 2021 15:08 #12

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Replied by treeves on topic Rebuilding my Dt 360a motor

I should have asked a question.
Is 1 pound in 20 minutes nothing to worry about?
What head temp would be the max?
19 Jul 2021 18:09 #13

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Replied by turbodan on topic Rebuilding my Dt 360a motor

Zero leakage would be ideal but I think you're alright with 1 pound loss over 20 minutes.  You could pull the pipe and head and give the cylinder base nuts another ugga dugga in case the gasket has compressed slightly and they aren't as tight as they were after initial assembly.  The reed block and carb holder can be difficult to seal up as well, some liquid sealant and additional gaskets can help here.

In my experience the DT360A is prone to carburetion problems.  You'll think you have it sorted but take it out for a long ride on a hot day and the revs start to hang again and the pinging sets in.  I hesitate to claim I have resolved the issue on mine but if it's not 100% it's close to it.  Keihin carb, modern 250cc reed block, cylinder porting, crankcase stuffing, modern ignition, MX360 pipe.  Most of those changes had little effect by themselves.  Oddly enough the big reed block seemed to help, though I changed a few other things at the same time too.  Perhaps it allows a stronger intake signal to the carb.  The stock block is absurdly small, but luckily there is enough meat in the casting to make room for something a little more appropriate.

Anything over 400 degrees at the head would make me uncomfortable.  Between the carburetion difficulties and primitive CDI it's pretty easy to catch these things running hot.
19 Jul 2021 20:55 #14

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Replied by RT325 on topic Rebuilding my Dt 360a motor

Hanging a bit makes me think its holding onto advance then flicking to retard electronically. But that isn't going to happen. Retard for starting on those is really only kick speed plus a few hundred revs. I could feel mine retard but idle was so slow it was almost stalling. Is it sitting just above idle, not further up--then drop down & idle good not faltering like starving. Theory--if the idle is too rich then you have to screw the speed up to keep it from stopping. But after a run it's forgotten about its rich idle mixture so idles very fast until the rich idle catches up & drags it back down. Could 'almost' say the same for a lean idle as you screw the speed up a bit to keep it from stalling but after a run it idles even faster, but in that case-- if anything--it would probably try to slow down but fade away & stop.
Last edit: 19 Jul 2021 23:01 by RT325.
19 Jul 2021 22:57 #15

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Replied by treeves on topic Rebuilding my Dt 360a motor

Turbodan and rt325 thanks for the posts. I think I will put bike back together and forget about the pressure test.  This is the 2nd time I have done a pressure test on this bike the first time I did find leaks in the manifold and also my test equipment, I did seal the manifold with liquid sealer and one of the screws. I also found leak in my compression release.  I have taken care of these problems but can't find any other leaks.  The bike will idle at 1500 rpm and when hot and at say 4000 rpm let off gas the engine will hesitate at maybe 2500 then go to idle.  That is why I did a 2nd pressure test.
I put the temp gauge on bike with the idea of knowing a max temp so I don't seize the piston, so thanks for the 400 degrees.
I think I may have an exhaust leak.
Thanks again 



 
20 Jul 2021 08:33 #16

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Replied by Pedalcrazy on topic Rebuilding my Dt 360a motor

They did the same work and pit filling on my crank for my 76 DT400. Beautiful work and first rate communication. I'll use them again. Bill Bune in Minnesota does crank work too. Good luck with your build.
1978 DT400E
1976 DT400C
1973 RT3
1971 RT1B
1968 DT1 (3)
20 Jul 2021 18:28 #17

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Replied by DT400FRANK on topic Rebuilding my Dt 360a motor

What do you think the cost of refurbishing a dt400e crank would be?
20 Jul 2021 20:20 #18

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Replied by treeves on topic Rebuilding my Dt 360a motor

The cost for the 360 was to rebuild crank 95 dollars, if you have pitting on seal area 145 plus a new rod and shipping
21 Jul 2021 07:54 #19

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Replied by Jack on topic Rebuilding my Dt 360a motor

Bill Bune charges 60 to rebuild crank. That doesn't include parts of course. If I remember correctly shipping was around 30 bucks from Missouri but that included a complete crank/rod kit plus my cylinder which I sent along with the crank. They did an excellent job. 
21 Jul 2021 10:11 #20

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