DASA Diagnosis

brad95

brad95

Well..
After a good weekend riding, on a new setup (not new engine) and 3 tanks of gas it came to a quick end.

Dasa 1100 95x10, 200psi, straight av100ll / avgas. Charging 64x/zeeltronic at 32*. Squish was .034" Engine had probably 30hrs on pump fuel 175psi.

Novi 48s, 125 return jet, 1.5psi at idle 4psi at 3/4 throttle. 125l 135m 22psi pop off. Engine ran well, still rich, could not get it to bog need to get some smaller jets. Engine also ran fairly cool. But warm to touch so not too cold?

Rode it very easy, checking plugs every time, 3 tanks of gas. always looked really good. loaded it up for a few slide flips. Did 5. Engine pulled clean. 6th time it died whilst still slidding backwards.

Anyone have any input? Ring caught a port, is this from excessive cylinder pressure from detonation or running more cylinder pressure from before and the port not being chamfered enough? Any ideas?20210405_090820.jpg20210405_090708.jpg20210405_090411.jpg20210405_090559.jpg20210403_174513.jpg20210405_110747.jpg
 
brad95

brad95

Piston to bore was set from machine shop. I gave them the pistons and box with spec sheet. Also the ports chamfer and ring gap. I remeber them saying the ring gap is pre set and checked ok. They are who i use for my v8/LS machine work not very much 2stroke experience.

After watching one of erickson machines YouTube video he really puts a large radius on the ports. These are very minimal as you said.
 
Jcary85

Jcary85

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Location
Glenmoore pa
I don’t think you were detonating running Av gas on 200 psi. Was there any water in it? Possible a cooling line came off when sliding or something? I do see a good bit of chamfer on the first pic but it’s kinda hard to tell. Got any close ups of the plugs? Can look for signs of deto there
 
brad95

brad95

Both locating pins are still on the pistons/ring groove.
I do also believe theres no sign of detonation. Plugs always looked really good no sign at all. Dry as a bone also no water

Measured ring gap on rear cylinder .032" seems plenty if not almost too much? Those rings in front cylinder also measure .032". I dont have a dial bore gauge this big. But id expect the bores to be the right size. The weisco boxes had the final size and or clearance required noted on them from memory.

The ports do however have very minimal chamfer. Almost looks to be hand filled only not removed/polished with a diamond burr or so? Which is my fault at the end of the day for not being more thorough when assembling. This was a long time ago, and i do know alot more than I used too. Have to learn from these mistakes. I dare say this is whats caused the ring to grab? Maybe not before but slightly increasing the cylinder pressure with more comp and aggressive timing has caused the ring to expand that tiny bit more than before?

Good news is crank seems really good. Center bearings seem perfect. Rear bearing perfect. Front the slightest bit worn. I will replace both front and rears. And check straightness/run out. 20210406_041444.jpg20210406_050455.jpg20210406_050602.jpg20210406_050708.jpg
 
brad95

brad95

What should it be, like a nice .030-.040 radius?
Concering part is the aluminum being hurt behind the sleeve. Once i bore the sleeves out this should be able to be repaired hopefully?
 
TheBuzzard

TheBuzzard

Location
the jetski grave yard
It gets heated up and sleeve slides out. Yea very little chamfer. If they dont know 2 stroke , they dont know about chamfer. Needs to be ground way out. I forget now but I think rings snag on the way down not up. So critical on lower edges. Better to pay dasa to do it right than your local car motor guy to half ass it. Squish sounded pretty tight for that large of bore too. Not that that caused it
 
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