The Cessna 120-140 Association Forum

So I’m starting to sweat an impulse purchase for my 1946 C-140 with an O-200. I currently have for a prop a McCauley 1A100 6950 MCM. Fits on the prop flange which has larger bushed bolt “dowels”. So I jumped on a McCauley 1A101 PCM 6948 for sale. Went to bolt it on and bam! It has the narrow bolt holes with no allowance for the dowels on the back of the prop.

Does anyone have any good ideas? Spacer available? Anyone run into this bump in the road before? Hoping I didn’t just purchase a $850 wall hangar.

Thanks in advance for the info!

A prop shop should be able to turn it into a DCM that will fit the O-200.

Thank you for the reply Randy! I’ll hold my breath $$$$

Can someone explain the difference between MCM and DCM.
I have a 1A101 pitched at 48, but never realized the MCM and DCM difference between the props.

The later 150’s use a forward spacer that fits on the crankshaft flange with longer bolts. The MCM is for this setup. The DCM has enlarged holes on the backside and fits right onto the crankshaft flange.

Talk about confusing. My 1A100 is an MCM which has the larger bolt holes on the back of the prop to accept the flange. Maybe they were bored out as you suggest for my 1A101 PCM Prop.

The info you're looking for can be found in Note 1 of the propeller type certificate, P-918:

Models 1A100/MCM, 1A105/SCM and 1A101/DCM are for installation on SAE No. 1 flanged propeller
shaft and must be installed in accordance with McCauley Drawing B-1161.
...

Models 1A102/OCM and 1A101/PCM are for installation on SAE No. 1 flanged propeller shaft with
McCauley P/N C-4513 spacer and must be installed in accordance with McCauley Drawing B-4515.

I happened to find the spacer C-4513 for a reasonable price. That would be acceptable with the O-200 stc? Sorry for the foolish questions....if so, on to find the bolts. Also, are the dowels built into the spacer or is that a seperate part?


Also called two prop shops on changing it from a PCM to DCM and got a negative on that. Bummer

Randy O

Well, technically, your O-200 STC lists the applicable props. Sounds like the PCM is not one of those listed.

I'd contact McCauley directly about the model change. If they say yes, maybe they can tell you who would be able to do it for you.

Adding the spacer is going to move the prop forward from the cowl. If that's desirable I can't say. I'm guessing the 150s that prop was used on have a different cowl from the earlier ones.

Thank you John for the explanations. I'll go read that TCDS