Coltri project
Started to build a compressor for myself, found a used coltri mch6 head unit with busted fourth stage. Took it apart and replaced conrod bearings and coated crank with ceramic coating to reduce friction and wear.
Fourth stage piston coated also.
Couple of pics of the project so far.
Marko
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Fantastic MJP!
Cylinder without cooling sleeve, ready for hardening.
Marko
Yeah, fragments and very small at that. The piston stump hit the cylinder on down stroke and stopped the pump from 1800rpm.
Cylinder is a write off, it has a hairline crack in it.
42crmo4 barstock arrived yesterday so I’ll be making new piston and cylinder as well.
I’ll make it a little different from original, crmo liner and alu cooling skirt press fitted on top to aid cooling.
I hope the hardening goes ok the first time, sometimes parts may crack durring quenching in oil.
Marko
That cylinder took a hard whack from something. Did you find the pieces in the crankcase?
Double trouble, did find more damage when pulled the cylinder. Part cracked from the cylinder.
Need to think this for a moment or two.
Marko
Well yeah, ouch. Obviously the piston didn’t like me cutting ring grooves on it, it was too hard material and snapped from the bottom groove.
Oh well, need to turn new piston from 42crmo4 harden it and coat it like the first time, lapping it to the cylinder and not cutting ring grooves. Need to make new rod from 7075 but that’s no problem.
Marko
Ouch!
Fuck, not very good start for airgun season.
Number four piston broke in two, stopped dead from full chat…
No collateral damage except the rod, it bent.
Marko
Ok so had little problem, it wasn’t the fourth that was giving me grief, third had a two broken piston rings, and the C expander springs had scratched the cylinder slightly, turned it in the lathe to 19.05mm and made new oversized rings out of teflon. Let’s see how long it lasts. It got only 0.05mm bigger so nothing major.
Back together and fills ok to 310bar didn’t run her flat out but around 80% throttle and well got ~80L/min filling two 10L 200bar bottles from empty. Some blow by but it’s not new anyways. Table spoon of oil water mix from those two fills, and some water, I can live with it.
Marko
Basically same thing, coltri uses them in the third stage and now mine has them on fourth.
Needs a new belt, now that all the stages work again the belt started to slip pretty bad, didn’t want to smoke the whole garage so had to turn it off middle of the fill.
The belt was already worn and some oil got to it durring the winter and I forgot to get a new one.
So testing again tomorrow I hope.
Ordered intake filter housing some time ago and had to ask Ray some specs before I used it, so thanks to Ray for quick answers!
Marko
Reminds me of the steel spring ring inside the phenolic rings of the Mrodair. Well, neat that you can make your own rings. No supply problems.
It started to slow down again sometime at fall and the pressure suddenly dropped on one fill to 220 bar.
Well had time yesterday finally check it out and number four is out again, this time the ptfe rings I made where little worn, but the reason the pressure dropped was the O-rings under the rings where cut so they didn’t expand the rings anymore.
Made new rings with springsteel c shape expanding rings in them like on third stage teflon rings.
Will be assembling it today and let’s see how she runs again.
Maybe I need to order complete fourth stage kit for it if this doesn’t work.
Although it costs nothing to swap the rings once and awhile and it’ll makes sure I change the oil often enough. :rofl:
Marko
Ok so time for update, the compressor had worked good until last week, had a bit more blowby and didn’t work as fast as before and then stopped to make 300bar. So the ceramic coating I used to fix the worn fourth stage piston doesn’t last as long as I had hoped.
So time for something else, I cut two piston ring grooves 3.5mm wide to the piston and made split type ptfe rings with o-rings on top of conical seat in the rings.
As the pressure builds up it forces the o-ring deeper in to the conical Teflon ring expanding it against the cylinder wall.
It actually works, and fill time is reduced 200-300bar was around 17min when I first got it finished and now it’s around 11min on a 12l tank lets see how long it works, and if it doesn’t the fourth stage kit isn’t that expensive.
Sorry for not taking pictures, was in kind of a hurry.
Marko
Yeah, they are anodized I checked that when got them. Saved me the trouble of setting up my anodizing tanks for I have drained them.
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Thanks, hardened the cylinder today, and just realized I forgot to drill the side air passage to the cylinder. Guess I have to use carbide endmill to drill the hole now.
It turned out pretty hard, normal metal file can’t touch it.
Marko