I think they chose sintered metal because it does the job and doesn't require machine work. A given amount of powder, in a die,tremendous pressure is applied, boom ,,you have a part. Why they didn't radius in the corners, IDK. Maybe it's not important with sintered metal.
But they Do break.  

I went back to the machine shop today so we could perform a hardness test on the OEM and AR500 parts.  The test used was a surface hardness test only.  The hardness on the sintered metal is an unknown - we really don't know anything about the composition of the sintered metal, either.  All we can do is run comparison tests.

OEM PART
We tested two OEM parts, twice each.  The hardness readings were Rockwell C 39.5  The readings between the four tests, two on each part, was very consistent.  In the picture, one OEM part has three dimples - the third dimple is from the initial test we did when I brought him the part to inquire on a mfg run.

AR500 PART
We only tested one part, but took multiple readings.  The readings were (again Rockwell C scale) 37, 39, and 40.3  The reading were not as consistent as the OEM sintered part, but very close to the same hardness.

Since the AR500 is rated at an average of 48 C, some temper was lost during the laser cut heating the part.  The depth of cut versus the cross section of the part configuration contributed to this.  He estimated the parts could have gotten upwards of 5-600 degrees for a short period of time.  This hardness test is a surface test only, and does not reveal anything about the tensile strength throughout the cross section of either part.

I have decided that since I am not willing to spend money on fixtures or gages to measure destructive strength tests that accurately duplicate the force applied in the design application, I will go ahead and ship the parts to whoever is interested in running one.  I know that this material is no where near as brittle as sintered metal.  I am not willing to invest any more money into trying to prove it.  Feel free to do your own research on the physical properties of each of the two materials (we don't know the composition of the OEM material,  but there is a lot of data on the powdered metal process pros and cons).  If the people that were interested initially still want to buy one or more, PM me your addresses and I will start to get postage or shipping costs.  If you decide not to, that's okay too.  It is my conclusion that the OEM part failures are more than likely due to the sintering process yielding inconsistent part strength - possibly due to material flaws during processing.   Peace, out.

I think more important than how "brittle" the material is - would be the "tensile" strength.

I certainly don't know much about powder metal - but it would seem to me that the compressive strength readings of the sintered metal could be similar to steel - while the tensile strength could be far lower.  The heating and congealing of metal powder could create a part that is resistant to compression - but not nearly as good in tension.  (The thin part of the pawl is breaking under tension.....not compression).

Send me my 3, and I am likely to set something up and see what "gives"!  

Thanks very much for those hardness readings.  The two parts are amazingly close in hardness. For carbon and low alloy steel, RC 39 to 40 should correlate to approximately 177 to 184 ksi tensile.  I agree that the wrought material should be more resistant to fracture.

Since the AR500 is billed in the tensile range of about 240 ksi it seems as if it has lost some of its hardness as a result of the laser cut.  That might be a good thing.  Might improve ductility, make it less prone to fracture.

Totally cool how you got these things manufactured so fast.  You seem to have a really good connection with the machine shop, and the shop seems to have remarkable capability.

badwolf wrote on 01/30/22 at 08:28:56:


Let me know if you are still interested.

4/8/22 Continuation – Testing Sneezy’s Release Cam

The clutch now has 13,300 miles on it.  Aside from one false alarm when the transmission failed, it has performed flawlessly.  All of the clutch components checked out perfectly and I reinstalled it in my spare engine.  I’ve been running it in the spare engine for several months now.  That engine is no slouch, so the special clutch is seeing plenty of torque.  It works good.

I wanted to install one of Sneezy’s special release cams when I assembled the spare engine, but I wasn’t completely sure that the AR500 cam would hack it, so the spare went back together with a stock release cam.

I am waiting for various parts to forge ahead with my new 97mm flat-top engine, so I had some breathing room to mess around with the release cam.  Time to see how strong Sneezy’s hot-rod release cam is.

To do a proper test, you need to know how much force the stock system is subjected to.  I had this old beater tool for Harleys.  It was perfect for measuring torque on the Savage release lever.

Now I needed a way to twist up the release cams.  A grade-8 bolt fit the bill.  Super strong, super cheap, machinable.  An hour or so later I had this.

A look from a different angle.  I think this will approximate actual conditions.