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Post by oldgeek on Feb 19, 2017 22:01:20 GMT -5
I have been trimming the piston skirt and piston transfer area just a bit.    Not having much luck truing the crank up, and also have just about decided I am not happy with how loose the piston fits in the cylinder. With all that in mind, I have been searching around for a decent crank, possibly a name brand crank. They seem to be making some for the bigger cylinders now. Top Performances crank MVT crankAlso I would really like to know the durations of the autotech 54mm aluminium cylinder if anyone knows? |
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Post by 'O'Verse on Feb 19, 2017 22:26:21 GMT -5
The only person I know to run the aluminum 54mm was Mauibird. He might remember what they were before he had them changed.
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Post by gsx600racer on Feb 20, 2017 2:04:02 GMT -5
Thanks for the offer nelson , if I end up going 52mm I will take you up on it. I spent a lot of time tonight looking at and thinking about the 2 stroke ports and the way they work/interact. Not so much the exhaust and pipe, but the way the transfers and the boost port work with the piston. I feel like I know even less now than when I started! Lol. There is a whole lotta stuff going on at both sides of the piston in a 2T engine! I also tried my hand at crank truing, it seems to be as mysterious as the 2 stroke cycle. It aint easy, I give props to those that can do it. I got the stuffer crank trued measurably better, but not buy much. I can see the runout on the flywheel side when the crank is turned by hand so I know it will have to be better than that. When I started working on it, the dial indicator was swinging over 4 marks, I have it down to 3 marks now. Each mark is a thousandth? I trued one of mine a couple weeks ago on a friends lathe. After bucking a center in a 6 jaw chuck I supported the crank on centers. I used the cross slide and the tool rest to "manipulate" the cranks run out. Basically had the push crank beyond the run out so when it "sprung back" and rechecked the run out. It took a couple hours to get the feel of learning how to tweak the crank in the opposite direction to correct the overall run out. |
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Post by 190mech on Feb 20, 2017 4:44:11 GMT -5
You can check the piston to bore clearance with a feeler gauge,should run fine between .0015 to .003"..I'll be glad to give that crank a try at truing if you want to send it to me..
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Post by oldgeek on Feb 25, 2017 22:23:14 GMT -5
Have not been able to find my long feeler gauges to check piston/cylinder clearance yet.
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Post by oldgeek on Feb 27, 2017 22:35:10 GMT -5
I watched some crank truing vids and read a couple threads on the subject so I took another shot at the 90cc the crank. I had it swinging less than 1 mark on the dial indicator so I think that will do. I still need to work out the piston to cylinder situation.
Do they still knurl pistons now days?
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Post by oldgeek on Mar 12, 2017 21:19:35 GMT -5
I found my long feeler gauges and checked the piston to bore clearance. Stacked a .003 and a .002 = .005 and it is just still a bit loose to pull out. I can get .0065 in and it is fairly tight. So I guess I need a new kit or find an oversized piston somewhere.
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Post by gsx600racer on Mar 12, 2017 22:45:56 GMT -5
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Post by stepthrutuner on Mar 13, 2017 0:35:18 GMT -5
My RS70II is really torquey right off the bottom but carries a little into the 10k range with exh. duration in the 190 deg. range. Disp.of 74cc. Steady power with no discernable hit. Looking forward to your results.
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Post by tsimi on Mar 13, 2017 2:06:29 GMT -5
Wish I had a working space like the dude in the video above.  |
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Post by 190mech on Mar 13, 2017 18:38:02 GMT -5
I have been trimming the piston skirt and piston transfer area just a bit.    Not having much luck truing the crank up, and also have just about decided I am not happy with how loose the piston fits in the cylinder. With all that in mind, I have been searching around for a decent crank, possibly a name brand crank. They seem to be making some for the bigger cylinders now. Top Performances crank MVT crankAlso I would really like to know the durations of the autotech 54mm aluminium cylinder if anyone knows? As to piston to bore clearance,,the piston in the pic looks used,is the cylinder also used?That may be the reason it has excessive clearance.If youve got a decent digital caliper and measure the piston,perhaps a replacement will get it back to a proper fit.. |
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Post by oldgeek on Mar 13, 2017 18:43:55 GMT -5
Yes, the kit is from my first attempt with a 100cc shortcase. I had very limited success with it. As I look back on that thread I remember now that there was excessive clearance on this kit when it was brand new. I have a new 52mm kit that also has .005 clearance so.......  |
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Post by 190mech on Mar 13, 2017 18:50:11 GMT -5
It'll run fine at .005,some slap will be heard and if run long enough a skirt will crack,its paid for though and 'in stock',,I'd run it!!  |
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Post by oldgeek on Mar 13, 2017 18:59:29 GMT -5
It'll run fine at .005,some slap will be heard and if run long enough a skirt will crack,its paid for though and 'in stock',,I'd run it!! I emailed Carlos (autotech) to see if he has any 54 - 52 mm oversized pistons, but I have not heard back from him yet. |
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Post by 190mech on Mar 13, 2017 19:08:48 GMT -5
The 54 already has some very thin cylinder skirts,,perhaps a .25mm(.010")would clean it up,the 52 has a lot more room for oversize..How are you doing the feeler gauge measurement?I remember the Wiseco bore sheet called out a 4lb pull on the feeler gauge to check clearance..
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