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DieselJim (Mechanical) (OP)
29 Mar 11 9:34
In our diesel engine remanufacturing operation we have a series of engines that use a timing belt to drive the camshaft, which in turn operates both the valves and the individual injection pumps.

The original surface roughness of the pulley teeth is Rz6 for the steel camshaft pulley and Rz15 for the sintered crankshaft pulley.

Does anyone have an idea of surface roughness limits for timing belt pulley teeth? For cleaning, we can soda blast (no influence on surface but expensive & time consuming) or aluminum oxide or ceramic bead blast (rougher surface but cheaper & faster).


Helpful Member!  swall (Materials)
29 Mar 11 12:52
What about just leaving them alone?
RossABQ (Mechanical)
3 Apr 11 10:58
Are the roughnesses quoted for "original" a mfr's spec or observed?  

Do these really get so much buildup that they need blasting of any sort, in lieu of chemical cleaning?
DieselJim (Mechanical) (OP)
7 Apr 11 11:39
Thanks for the input. The issue is making the determination of "clean", the persons working in the engine disassembly and cleaning of small parts areas have a large number of parts to process as quickly as possible, therefore we don't take the time to use too many specific processes to clean the parts before sending them on for inspection. In some cases these parts are caked with oil residue (these are industrial diesels), the engines are in our facility because they have failed and are generally in poor condition. The blasting takes very little time and the part is CLEAN, which aids the part inspectors. If we can continue this process without a negative impact on the part's function it is the most cost effective way. If, however, we are introducing a potential belt life issue we certainly want to avoid it, regardless of extra time needed to process the parts.
MikeHalloran (Mechanical)
7 Apr 11 11:53
Bear in mind that timing belt teeth are faced with fabric.  Presence of any kind of abrasive particle is not going to do them any good.  

Mike Halloran
Pembroke Pines, FL, USA

RossABQ (Mechanical)
7 Apr 11 18:10
I'd vote for chemical cleaning, i.e., just the same as an engine part, hot caustic solution.
patprimmer (Publican)
7 Apr 11 18:28

Unless of course they have aluminium components.

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RossABQ (Mechanical)
8 Apr 11 0:28
Whatever is used in commercial automotive hot tanks, it is safe for aluminum.  My understanding is that it is some kind of caustic, probably not radically so.  Your caution is correct if there are any copper-bearing materials or babbit.
patprimmer (Publican)
8 Apr 11 2:58
Caustic eats aluminium quite aggressively, so I doubt it is very caustic if aluminium is involved.

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Gearloose1 (Petroleum)
25 Apr 11 11:41

The problem with diesels is they tend to get carbon deposits that can be thick, and nearly impossible to get off without chipping / shot blasting.

The problem deposits tend to be at the other end of the gear (where the valves are, and engine oil drop those deposits).

The other end (the belt / gear side) tends to be quite clean.

Ideally, it would be chemical clean only on the gear side, as you really don't want abrasives left behind that can kill a belt faster than you say boo.

But the other side... hmmm

There may be no way out of this one except chemical.
stimpy1966 (Automotive)
5 Oct 11 2:57
a little late than never , ultrasonic cleaner , as blasting can hide cracks in the gears by peening the surface over , ultra sound cleans baked on carbon off quick and degreases real good so you can Pt test them  

making people scratch there heads for 40 years ..  

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