[Scott Diffenbaugh]

From the beginning, I always experienced slow cranking on our 0-360 with an Odyssey PC-680 battery and MagnaFlight MZ6222 lightweight starter. I would have to bump the starter to get the prop past compression. In 3 years, I purchased 3 Odyssey batteries because when they got a tad weak, (12.1 v with master switch on) and it was cold, the engine would not crank. My research indicated that some others were having the same problem, and solutions ranged from changing to a larger amperage battery to increasing the charging voltage from 14.3 to 14.6, (the latter I did to no avail). I was bemoaning my problems to Bill @ B&C while ordering a new Odyssey with a fresh manufacture date when he asked which starter I had. When I told him it was a MagnaFlight, he said it was without a doubt the problem, & was not even a good boat anchor (too light). I followed his directions and confirmed the starter was drawing up to 600 amps and the voltage at the starter dropped to 8.4v, when it should be drawing 250 to 300A @ 10+V. He explained the MagnaFlight was a permanent magnet design, cheaply made, versus his being series wound, with ball bearings and metal gears, @ 10.2#.
So, in July 2009, I purchased a B&C BCS20C-149 for $567 delivered. The B&C starter spins the engine twice as fast with no bump & the voltage only drops to 10.7v. I did not take the time to set up my video camera to check the amperage draw, but it has to be significantly less. In fact, I may have the only hybrid RV since I pull the mixture during flight & fly using the starter, until the battery drains down, then I restart the engine! I waited until now to write my report to see if 40 degree weather would slow the cranking. I am happy to report there is no difference. I now have two spare perfectly good Odyssey batteries that I use to power my GPS simulator at home. Case closed!
P.S. There are many factors that can affect cranking, so do not assume a new starter will solve your problem until you have ruled out everything else or have done a draw test.

 

[sprucemoose]

Scott,

What you just described is a well known phenomenon with lightweight (permanent magnet) starters. The missing piece of data from your post is the type of prop. The flywheel inertia of a heavy prop (ie. Hartzell) will often be enough to overcome this issue, but if you have a lightweight prop, you're toast.

So, what kind of prop do you have?

 

[Scott Diffenbaugh]

I do indeed have a lightweight prop, a 3 blade MT.

 

[RV8R999]

Scott - where is your battery located and what size? The length and size of cable from battery to starter is another factor. The shorter the better.

thanks,

Ken

 

[Scott Diffenbaugh]

Ken, The battery is an Odyssey PC680, 16AH located in the standard location on the engine side of the firewall, all per Vans. The cable is 30" of #2 & there was little difference in voltage between the battery & the starter when cranking attributable to the cable. This is clearly a case of a piece of junk starter as I thought when I disassembled it for cleaning and maintenance at the required 50 hours. I should have replaced it then and saved a lot of time and $.

 

[RV8R999]

Thanks Scott. I was afraid you'd say that. Exactly the set-up I have now and turning a wood sensenich won't help either. I did have this on a different airframe with the battery in a baggage compartment but was turning a Hartzell C/S prop. Still had to "bump" the starter past the first compression stroke and hoped that having the battery up front would solve the issue. Guess not.