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Engine Discussion of preventative/corrective maintenance and other technical issues regarding your coach's engine.

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  #11  
Old 11-24-2008
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Old Hardware Old Hardware is offline
1987 FC35 "Traveller"
 
Join Date: Feb 2008
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Mile,
I have had neither a '78 FC or an '82 FC tachometer in my hands so I cannot tell you exactly what you have there, however I did have a '77 FC and I know what type of tachometer pickup you have looking at the picture.

On my '77 FC a DC generator was used. There was a potentiometer on the back of the meter for adjustment.

The picture of the '82 is that of a reluctance type pickup tachometer. It uses the tooth mass on a gear to derive an AC signal as the tooth passes the head pickup magnetic center with a coil wrapped around it. The pickup is generally set a few thousands of an inch away from the gear, say .012-.015". Calibration is done dividing the number of teeth past the headper engine revolution, the relationship of the gear to the crankshaft, and 60 the number of seconds in a minute. The back of the tachometer will have "dip" switches for making this setting.

An alternator has an AC output as well (at the field winding level internally) not the output. A competent alternator shop can make you an external insulated lug through the back for an AC output signal. Not much, I think I paid $25 which included checking the bearings, diodes, and DC output voltage.

To me it would be much simpler to go the alternator pick up approach. Will the tach gage in the '82 fit the '78 in hole size and appearance?
Bob
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87 FC35 "Traveller"
Greenville, SC
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  #12  
Old 11-24-2008
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John 'n Deb John 'n Deb is offline
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Join Date: Jan 2008
Location: Carvel AB Canada
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Default horton fan

Our 84 Fc has a horton air clutch fan with override switch on the dash. Replaced bearings in fan last time i changed the belts.

John
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75 boler
Carvel AB Canada
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  #13  
Old 11-25-2008
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Burnin Up in Az. :-)
 
Join Date: Apr 2008
Location: Mesa
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Quote:
Originally Posted by Old Hardware View Post
Mile,
I have had neither a '78 FC or an '82 FC tachometer in my hands so I cannot tell you exactly what you have there, however I did have a '77 FC and I know what type of tachometer pickup you have looking at the picture.

On my '77 FC a DC generator was used. There was a potentiometer on the back of the meter for adjustment.

The picture of the '82 is that of a reluctance type pickup tachometer. It uses the tooth mass on a gear to derive an AC signal as the tooth passes the head pickup magnetic center with a coil wrapped around it. The pickup is generally set a few thousands of an inch away from the gear, say .012-.015". Calibration is done dividing the number of teeth past the headper engine revolution, the relationship of the gear to the crankshaft, and 60 the number of seconds in a minute. The back of the tachometer will have "dip" switches for making this setting.

An alternator has an AC output as well (at the field winding level internally) not the output. A competent alternator shop can make you an external insulated lug through the back for an AC output signal. Not much, I think I paid $25 which included checking the bearings, diodes, and DC output voltage.

To me it would be much simpler to go the alternator pick up approach. Will the tach gage in the '82 fit the '78 in hole size and appearance?
Bob

Thanx Bob, Yes the holes appear to be the same. I'm thinking I'll update and use the 82 tach and just move the sending unit over too. Seems the black lead is just a ground so wondering if I can just ground that and use the single wire alreay plumbed to the dash? I can merely ground the gauge up there too.

Michael
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78FC35SB Wanderlodge - "Putz'n Around"
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  #14  
Old 12-01-2008
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rtpn60 rtpn60 is offline
Burnin Up in Az. :-)
 
Join Date: Apr 2008
Location: Mesa
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Quote:
Originally Posted by Old Hardware View Post
Mile,
I have had neither a '78 FC or an '82 FC tachometer in my hands so I cannot tell you exactly what you have there, however I did have a '77 FC and I know what type of tachometer pickup you have looking at the picture.

On my '77 FC a DC generator was used. There was a potentiometer on the back of the meter for adjustment.

The picture of the '82 is that of a reluctance type pickup tachometer. It uses the tooth mass on a gear to derive an AC signal as the tooth passes the head pickup magnetic center with a coil wrapped around it. The pickup is generally set a few thousands of an inch away from the gear, say .012-.015". Calibration is done dividing the number of teeth past the headper engine revolution, the relationship of the gear to the crankshaft, and 60 the number of seconds in a minute. The back of the tachometer will have "dip" switches for making this setting.

An alternator has an AC output as well (at the field winding level internally) not the output. A competent alternator shop can make you an external insulated lug through the back for an AC output signal. Not much, I think I paid $25 which included checking the bearings, diodes, and DC output voltage.

To me it would be much simpler to go the alternator pick up approach. Will the tach gage in the '82 fit the '78 in hole size and appearance?
Bob
Hey Bob, just an update. I think you are correct in the generator vs pulse generator for the tachometers. I ended up using the 82 setup as the gauge was physically damaged too when I received the bus. I also found the drive pin broke which was probably the original issue. I think the previous owner broke the gauge trying to troule shoot?
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78FC35SB Wanderlodge - "Putz'n Around"
'90 GL1500 Goldwing | '67 VW Rail | '82 CJ5 Jeep
eMail=Mike.Putz@cox.net | Web=http://mikeputz.com/
Solar = https://www.solarpenny.com/SearchResults.asp?Cat=257

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  #15  
Old 12-01-2008
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rtpn60 rtpn60 is offline
Burnin Up in Az. :-)
 
Join Date: Apr 2008
Location: Mesa
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Originally Posted by iamflagman View Post
The Horton fan is activated through a themoswitch and a pneumatic switch, the electric override switch is tied into the themoswitch wiring.

There are actually two wires on the tach sending unit, in the photo the black wire looks like a shadow of the white wire.

As long as you get the proper themoswitch installed, under normal driving conditions it will handle any temperature, the override just comes in handy when you are about to start up a long grade to get a head start on the cooling. mine handles 110 degrees last summer in Wyoming and Montana pulling my enclosed trailer at 62 feet overall and 44,000 pounds gross. You may want to have the radiator cleaned thoroughly. I have found like many others, that at times you may need to slow down and/or select a lower gear to aid in engine cooling.

As far as I know the coolant line on the compressor is stock, I haven't changed it myself.
Hey John,
Removed the 78 fan clutch assembly and compared to the '82 assembly. The 82 is from a school bus in Arizona so may be a little different than Wanderlodges. The 82 seems to have a large bulky area that I'm not sure what it is?
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78FC35SB Wanderlodge - "Putz'n Around"
'90 GL1500 Goldwing | '67 VW Rail | '82 CJ5 Jeep
eMail=Mike.Putz@cox.net | Web=http://mikeputz.com/
Solar = https://www.solarpenny.com/SearchResults.asp?Cat=257

FMCA #236459, Good Sam #17270530, Vintage Birds #1509
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