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Small Cam Cummins Compressor and Turbo Questions
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By Rustymachine - Friday, July 22, 2011 8:06 AM
How often should my air compressor be cycling on and off? I don't have any discernable leaks in the plumbing but once we get to 120lbs, the unloader kicks in, truck leaks down pretty quick and the compressor comes back on again. When the truck is off at 120lbs of air, it seems to leak out through the compressor. Do I have an unloader issue? Is the compressor itself shot? Any thoughts on diagnosing the problem?
While I'm at it: Some goofy stuff going on with the turbo as well: I don't think this is the proper clamp on this turbo. It's not the original Cummins turbo. Grandpa installed this one for more swat back in the day. It's a Schwitzer. No tag on it, but I've captured the casting numbers on the exhaust side. Is the band clamp a readily available part? Do all Schwitzers use the same band? Exhaust catalogs just reference a Cummins turbo for band clamps and as this one isn't stock, I'd like to have more info for the parts counter. Can I just measure the diameter and buy a V-band clamp to fit that? Sorry for all the questions, but I've got a week of vacation coming and I'm blowing my hard-earned cash on truck parts. :)




It's a small cam Cummins 350 engine in a 1973 KW W900. Air compressor is a Bendix Tu-Flo 600. I'd appreciate any experience you guys are willing to share.

Thanks for your time,

By Geoff Weeks - Friday, July 22, 2011 8:19 AM
I think I'm doing good if my compressor kicks in once every 45 mins while traveling down the hiway (with air ride truck and trailer). Less then every 15 mins or so and you need to start looking for leaks. Lots of times the discharge hose with leak thru the wall (it gets hot and bakes the rubber, which starts to leak) and there will be no "hiss" but if you spray it with soapy water will be all "fuzzy" with soap bubbles. Othe places to look at are the unloader and ari drier if equipt. Air leaks can almost always be found with a soapy water soloution ( much easyer to find the a draw on the battery). Air tanks can have pin holes, and hoses can leak almost anywhere.

  Try Michigan Turbo for the band.
By Rustymachine - Friday, July 22, 2011 8:29 AM
Thanks for the quick reply.  I've got some work to do.  We are cycling at least every two minutes or so.  Looks like I'm going to try to air it up with a garage compressor and find the issue. 

By Rustymachine - Friday, July 22, 2011 10:19 AM
Should have searched first.  Found a good thread where Mr. Akers and Mr. Weeks discussed troubleshooting the system.  A search on "compressor" turned it up.

By wayne graham - Saturday, July 23, 2011 11:59 AM
Matt, don;t want to get in the middle of those who know far more than me but if your compressor is cycling every 2 min and you can hear air from compressor when shut off I would take a look at unloader valve That is just me. Wayne
By dashby - Saturday, July 23, 2011 4:18 PM
I'd think the check valve is bleeding air back to the compressor.

By glenn akers - Saturday, July 23, 2011 5:48 PM
You could take the intake off of the compressor head and when the comp cuts off listen for air leaking back thru the intake. If so then you need a field maintence kit installed which will be exhaust and intake valves or just replace compressor.