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Post by mellow on Jun 28, 2013 22:45:19 GMT 1
Right,im asking this for a friend,who i have mentioned in bills post about his DT piston,as he rung me again tonight asking "WHY??" He bought a Mk1 125 lc. It has an allspeed and a cone filter. It did all of about 30 miles before a hole appeared in the piston crown,just like bills. So he got it rebored,nice new Mitika piston,it was then he showed me the barrel and it was a DT one. I told him that but he decided to fit it anyway. Moving on,he took it for another little ride and after about 20 miles it started getting sluggish so he stopped. He got it home,took the head off,and HEY PRESTO hole in top of piston again!!! I said surely the oil pump must be f**ked,he said surely if that was the case it would seize not just lose power,and surely wouldnt melt hole in top center of piston? SO.........IF ANYONE CAN EXPLAIN WHY A HOLE WOULD MELT IN THE TOP OF THE PISTON PLEASE LET ME KNOW SO I CAN LET HIM KNOW. He is so fed up with it it may even end up on ebay very soon. Thanks  |
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Post by Delbert on Jun 28, 2013 22:54:26 GMT 1
If its doing it that quick I would say the timing is way over advanced , weather the dt barrel has a part to play in that I couldnt say ,, has it got the correct crank ? First off I would check the timing
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Post by billbott on Jun 28, 2013 22:57:34 GMT 1
It's detonation mick.
The timing must be too advanced.
I am checking mine as soon as my new piston arrives. If you read my post I have found enough play in all the related components to advance the timing even though it's fixed.
I will report back .......
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Post by billbott on Jun 28, 2013 22:59:44 GMT 1
I will pm you my number when I sort it and we will sort your pals.
Either that or I will invite you to my Dt bonfire.....
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Post by mellow on Jun 28, 2013 23:33:38 GMT 1
i did explain that to him bill but he's just had enough of it now. Bought it so we could all go have a thrash about like we used to when 17 but all he has done is f**k around with it. I will tell him to check that timing though before he gets rid. Cheers. ps.....dont burn the DT...Swap it for a rare TY  |
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Post by midlifecrisisrd on Jun 29, 2013 11:30:33 GMT 1
125's are a nightmare.
Been mailing back and forth with billbot as we both have DT's with problems. Never had half as much running probs with a 350
Agree holing the piston that fast looks like too much advance but concerned as even as bill says you can get 4 degrees play surely that would not be so drastic as you get 4 degree offset woodruff keys which would do the same. Surely a DT is not that near the edge.
If it was weak mixture surely it would run like shit if weak enough to do that.
took the top end off mine last night ( mine runs very spluttery below 5k as if too rich or strangled and won't pull ) and found barrel on perfect standard bore and piston unmarked and showing no signs of wear but a lot of blow by on piston so rings defo need changed.
Thing I have never seen before is the whole inside of the crankcase is covered in black as if it has been burnt. Mains are worn but seals look intact and big end side clearance is within tolerance. Reeds look ok but did have some dirty fuel puddling at rear of carb.
It looks like it has been stored for a long time and I have seen rings jam in with lying which might be the case as it runs fine until it gets some heat in it which may be the piston expanding and binding the rings. Strangest thing is a 13mm restrictor in the outlet of the front pipe that bill's bike does not have so now unsure if that should be there or is causing the problem.
As said, 125's are a nightmare
Steve
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Post by midlifecrisisrd on Jun 30, 2013 11:26:20 GMT 1
On second thoughts bills bike holed at 5k revs which would be around max advance so maybe an extra 4 might push it over the edge.
Would still like to know if his actually went onto reserve at the same time or just lost power first.
Steve
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Post by billbott on Jul 1, 2013 7:27:46 GMT 1
Steve,
It did go onto reserve just prior to meltdown.
Maybe the exhaust is off a restricted UK model?
I have posted my timing findings in my "melted piston" thread - maybe worth a read.
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Post by midlifecrisisrd on Jul 1, 2013 7:44:00 GMT 1
Steve, It did go onto reserve just prior to meltdown. Maybe the exhaust is off a restricted UK model? I have posted my timing findings in my "melted piston" thread - maybe worth a read. I did have that thought about the exhaust. The bike had the servo and pv controller missing as well as the middle exhaust bracket so looks like it was used to de restrict a uk model. I suppose I'll have to check the jetting as well now to make sure. Leaning out running on to reserve and timing issues won't have helped your piston, I'll have a read. Steve |
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