Starter Motor Conversion

How to keep the Cessna 170 flying and airworthy.

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Postby cessna170bdriver » Sun Jul 09, 2006 4:27 pm

gahorn wrote:
cessna170bdriver wrote:...George, how does having a generator cause you to be able to read starter current on the ammeter? . ..
Miles

Immediately after starting many "cabin class" and larger airplanes, one of the "after start" checks is that the starter disengaged. On some airplanes, one way to do that check is to look at the generator output. If a large output (greater than normal battery re-charge rates), ...or in the case of our 170s, ... a larger than the normal 1-3 amp or so discharge rate of the ammeter... would indicate a large (huge actually) electrical draw. If there's not yet any avionics/lights turned on,...a large discharge in the vicinity of 10-20 amps or greater would indicate a huge electrical demand somewhere. Guess where. There's only one thing on these airplanes that draw more than taxi/lnding lites. ... :wink:

(An idling alternator might partially mask this large discharge.)


The way 170's are wired, starter current doesn't go through the ammeter, and therefore can't be measured by it. Even if the starter is drawing 100 amps, and the generator is offline, you'd never see it on the ammeter. Generator/alternator current to recharge the battery DOES go through the ammeter, so I would think that a larger than normal REcharge rate after the generator/alternator comes online would me more indicitave of a hung starter (the same indication would be given if the battery was in poor condition). In any case, a light connected to the armature of the starter would eliminate the guesswork, IMHO.

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Postby cessna170bdriver » Sun Jul 09, 2006 4:34 pm

N9149A wrote:John the torque specs are indeed in the overhaul manual. Look in the back under "Table of Specifications" (or something like that)


The overhaul manual does provide the most critical torques, but TCM service bulletin SB96-7C provides much greater detail. I would post a link, but you have to subscribe to TCM's "Aviator Services" for access. You can register free at http://www.tcmlink.com/registration/avi ... ation2.cfm and in the 7-8 months I've subscribed, I've received no junk mail or spam.

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Postby wa4jr » Mon Jul 10, 2006 11:20 am

I just finished looking....twice...in the two page specifications section at the front of the TCM overhaul manual and there are no fastener torque specs given :cry: Seems to me I saw a table of "general" torque values based upon fastener grade, size and thread pitch somewhere. Perhaps this is the general knowledge base that the TCM manual presumes an A&P to have, therefore no specific torque table is given. I'll subscibe to the additional service George listed and see if there is anything there.
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Postby cessna170bdriver » Mon Jul 10, 2006 2:49 pm

John,

I don't have my OH manual with me, but as I remember, the torques are listed as part the Table of Limits, after the overhaul instructions. Check your email for a copy of the service bulletin.

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Postby gahorn » Tue Jul 11, 2006 8:41 am

cessna170bdriver wrote:
gahorn wrote:
cessna170bdriver wrote:...George, how does having a generator cause you to be able to read starter current on the ammeter? . ..
Miles

Immediately after starting many "cabin class" and larger airplanes, one of the "after start" checks is that the starter disengaged. On some airplanes, one way to do that check is to look at the generator output. If a large output (greater than normal battery re-charge rates), ...or in the case of our 170s, ... a larger than the normal 1-3 amp or so discharge rate of the ammeter... would indicate a large (huge actually) electrical draw. If there's not yet any avionics/lights turned on,...a large discharge in the vicinity of 10-20 amps or greater would indicate a huge electrical demand somewhere. Guess where. There's only one thing on these airplanes that draw more than taxi/lnding lites. ... :wink:

(An idling alternator might partially mask this large discharge.)


The way 170's are wired, starter current doesn't go through the ammeter, and therefore can't be measured by it. Even if the starter is drawing 100 amps, and the generator is offline, you'd never see it on the ammeter. Generator/alternator current to recharge the battery DOES go through the ammeter, so I would think that a larger than normal REcharge rate after the generator/alternator comes online would me more indicitave of a hung starter (the same indication would be given if the battery was in poor condition). In any case, a light connected to the armature of the starter would eliminate the guesswork, IMHO.

Miles


That's exactly correct, Miles. I'm sorry I wasn't more clear.
The case that brought it to mind was one in which a Cessna 400 aircraft, if the starter remains engaged a very large Ammeter indication ...more than 50 Amps. Cessna 400 series ammeters do not show discharges, ... they are like Barons, ... the ammeters have ranges from 0 thru 100 or so (depending upon the actual size of the alternator/generator.) After an engine start the ammeter will indicate the current created by that alternator and life continutes.
If, after a start, the pilot sees an ammeter reading of 50A or more...then it's an indication that the starter has "hung up" and is still motoring. This is considered a serious malfunction, and the engine is to be shut down, and flight not attempted.
You are correct that with the original wiring diagram/plans, the C170's starter is not included in the ammeter circuit.... but it still has a major effect upon the battery... It will serioulsy discharge the battery. The way a pilot might detect this is, immediately after start, ... monitor the ammeter to see if it shows a large deviation from normal charge rates after starts.
'53 B-model N146YS SN:25713
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Postby cessna170bdriver » Tue Jul 11, 2006 2:47 pm

gahorn wrote:...C170's starter is not included in the ammeter circuit.... but it still has a major effect upon the battery... It will serioulsy discharge the battery. The way a pilot might detect this is, immediately after start, ... monitor the ammeter to see if it shows a large deviation from normal charge rates after starts.


...which would show up quicker if an alternator were installed than if a generator were installed. :wink: I think I'd rather detect a hung starter at 1000 rpm than 1500... or better yet, a light in the starter button showing power applied to the starter.

BTW, with my Jasco alternator and regulator, it takes about 1000 RPM to bring it on line, but it will then stay on line down as low as the engine will idle. Immediately after starting I get about a needle width of discharge, then after I've verified oil pressure I increase RPM until the alternator comes on line, which is indicated by about 1/4 to 1/3 scale on my 60-amp ammeter (15-20 amps) for a minute or two to top off the battery. It is about the same with the new starter as it was with the old.

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Postby wa4jr » Sat Jul 15, 2006 2:05 am

Received my B&C starter yesterday. I had to open the box to see if anything was in there besides the peanuts...it was soooo light. I got the very last starter they had for O-300 engine. Demand has caught them off guard and no more will be available for a few weeks. I have all the accessories off of the gear case. No problems except I did not note the orientation of the ignition harness on the rear of each mag. I'm counting on the "natural" tendancy of the plug wires to orient the connector block to the mag. I'm leaving the F&M oil filter head on the accessory case so I don't have to hunt down the crush washers. In the morning the case cover will come off and I'll be able to start cleaning things up and getting ready for the hack saw boogie :D With such tight quarters, I don't see how anybody gets a dremel tool up in there to cut away the shaft ala Skytec without at least some oil contamination. Oh yes, found the torque specs, what few there were, in the table of limits. I suppose the 5/16 bolts/nuts on the case will just go in "snug" so I can see some gasket compound ooozing 8)
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Postby gahorn » Sat Jul 15, 2006 10:20 pm

You can always pull the oil screens and flush the case out thoroughly.
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Postby wa4jr » Mon Aug 14, 2006 1:21 am

Now that Oshkosh is over, I have time to sit down and write. The B&C starter conversion was a resounding success. When I dropped the crankcase cover away from the engine, the gasket stayed on the engine so that it formed a buffer against stray hacksaw strokes. I used just a hacksaw blade on the pinion support shaft as using the hacksaw frame prevented me from getting the blade in far enough on the shaft. After the shaft was cut away, it was questionable whether or not I had the required 2.5 inch clearance for the new starter pinion to properly engage, so I took a die grinder and touched up the shaft knub a bit more...until the center hole just started to open up, then I stopped so as to prevent abrasive dust from spewing into the hole. Everything went back on without a problem, the starter button and circuit breaker installed, and it was time for a test. How sweeeet and clean this starter sounds compared to my old Delco Remy coffee grinder. The B&C quickly spins my engine up through the impulse coupling range as though there was no compression at all :o I get about 300 RPM on starter only. Oh, and that eternal drip of oil that always hung off the old pinion shaft plunger is gone forever....now I only have eight other leaks to find :wink: At Oshkosh, the B&C folks had a Skytec starter that they were showing off...complete with a cracked housing resulting from the casting process. The housing on the B&C starter is machined from a solid block of aluminium....cost more, but well worth the price to never ever have to worry about starter problems again :D
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Re: Starter Motor Conversion

Postby bgiesbrecht » Tue Mar 24, 2020 5:45 am

Resurrecting an old thread... for those of you that have done the B&C conversion, did you have to get a different battery? I have a relatively new RG-25 and the B&C can barely turn over. The battery is fully charged. Have yet to measure the amperage during cranking - I suppose there could be an issue downstream, but just curious if anyone had to get a beefier battery.
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Re: Starter Motor Conversion

Postby ghostflyer » Tue Mar 24, 2020 7:49 am

A serviceable R-25 battery should be fine for spinning your engine over but have it load checked and check all the connections and condition of wiring. How do you know the battery is fully charged? I use a R25 Concord battery and it spins a O-360 high compression 4 banger . I will not put a pink battery in my aircraft or any aircraft . At the back of our workshop we have a number of recycling boxes [6ftby6ft] .one of these boxes [we call it the battery box] is about 1/2 full and the recyclers will not accept the pink batteries. The city has offered to take then off our hands for legal disposal at $10 a battery.
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Re: Starter Motor Conversion

Postby c170b53 » Tue Mar 24, 2020 8:14 am

Not that’s there’s anything wrong with a battery being pink.....I’ve had good success with the Concorde RG.
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Re: Starter Motor Conversion

Postby lowNslow » Tue Mar 24, 2020 3:04 pm

bgiesbrecht wrote:Resurrecting an old thread... for those of you that have done the B&C conversion, did you have to get a different battery? I have a relatively new RG-25 and the B&C can barely turn over. The battery is fully charged. Have yet to measure the amperage during cranking - I suppose there could be an issue downstream, but just curious if anyone had to get a beefier battery.

I've been using a RG-25 with my B&C starter for years with no issues. Might check your connections and engine to airframe ground connection.
Karl
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Re: Starter Motor Conversion

Postby hilltop170 » Tue Mar 24, 2020 4:11 pm

My electrical problem checklist for any electrical problem is:

Battery condition
Connections
Switches
Contactors/solenoids
Breakers

I have had every one of those items fail and cause problems, from time to time.

The last failure I had was the original starter contactor/solenoid. It would pass enough current to show voltage but would not pass enough current to spin the starter. A new contactor did the trick.

Before that, the generator breaker would fail intermittently and not keep the battery charged enough to start. A new breaker did the trick.

Hopefully it is something simple and not the new starter itself.
Richard Pulley
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1951 170A, N1715D, s/n 20158, O-300D
Owned from 1973 to 1984.
Bought again in 2006 after 22 years.
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Re: Starter Motor Conversion

Postby cessna170bdriver » Tue Mar 24, 2020 7:17 pm

With a fresh Concord RG25 battery and the spark plugs removed, my B&C spins the engine at about 300 RPM. Even with the spark plugs installed it spins faster than the Delco ever did. If your battery is fresh you probably have a wiring problem, or maybe some bad connections. Have you checked the engine grounding?
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