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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It wasn’t built up pressuring inside the crankcase that was my concern when I saw the thin walls. I was more thinking about the mechanical stress the mounting points of each cylinder exerts on the crankcase walls. The piston force has to be resisted by the two bolts holding each cylinder onto the case. It’s probably fine, but I’m interested in knowing how much more (if there is more) leeway the Coltri’s construction allowing in its case castings.
BTW, how thick are the crankcase walls on your Coltri? I’m wondering whether the 0.1 inch thick, aluminum crankcase walls of the Mrodair Airmax are typical.
I don’t think that the .100 wall thickness is an issue at all. All the pressure is within the Heads (between the piston and the head) so if your getting pressure in the crankcase that is an issue. Otherwise it would be blowing oil everywhere…
Do you do the ceramic coating yourself or send the parts out to have them done?
BTW, how thick are the crankcase walls on your Coltri? I’m wondering whether the 0.1 inch thick, aluminum crankcase walls of the Mrodair Airmax are typical.
Well, not cars but bikes in the past. Drag racing and f1 sidecar road racing.
But anyways motorsports engine builder some time ago.
Ceramic coating on crank….. now there’s a racing car guy!
That’s great! Since the forth stage is located in the base of the block, it sits in the oil. If any moisture is allowed to collect in the oil, it will sit right on the forth stage assembly. That moisture will cause corrosion on the valve spring, plate and eventually the piston/cylinder.
Thanks.
No corrosion on the cylinders or pistons. Just a broken valve spring that got inside the fourth. Other than that all the pistons and bores are pristine. Valves and seats are clean and clear.
Marko
Interesting project! Since the forth stage broke, I would guess that the valve spring and plate are pretty much corroded. Inspect them, lap the plates and replace the springs on all the valves.
And make sure you give us a follow up on your project.
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I do coat my parts myself, it’s pretty simple really. Sandblast the surface to get good attachment of the ceramic coating, then heat the part around 30-35C and spray one even coating on the surface. Blow dry with heat gun and oven cure min. one hour at 150C.
The coltri casting is pretty beefy compared to mrod, about 5-6mm minimum and strengthening webbing around cylinder thread areas, and around bearing areas.
The mrod case is just fine, no more stress on high side than on normal shop comp, for the surface area is only 12mm for the piston, so crank and cylinder load is just about the same as 10 bar shop compressors what it’s originally designed for.
Marko