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Tach drive delete?

S

Smart_Solar

Member
So quick trip to Oshkosh and new Lycoming cylinders are ordered, getting serious about assembling an 0-360. I wanted to check with engine experts here on the current thoughts of deleting the tach drive during engine assembly. Reading through previous posts I have noticed cons with both approaches.

1. Engine destroyed because tach drive was operating unloaded and failed.

2 Engine destroyed because I removed the tach drive and all the oil departed the breather line.

Hoping for more encouraging advice that does not result in engine destruction.

-Bruce:confused:
 
Bruce, install the drive gear assemble. There is no downside to installing it.
If you delete it please report your findings.
 
Reassembly of my 540 saw me delete not only the tach drive shaft, but one magneto idler gear and shaft assembly, swapped the fuel pump eccentric idler with the just deleted idler gear, deleted the fuel pump pushrod, and the vacuum pump drive gear, shaft and housing.

One needs to evaluate oil flow when eliminating parts in the accessory case. Many (like the idler gear and vaccum pump drive) are integral to the pressure lubrication path. Many people pull the vaccum pump shaft and leave the housing, not realizing they have just created a massive internal oil leak.

Its great to reduce rotating mass, but think it through before you start deleting stuff.
 
I appreciate the thoughts and your experience. Looking at the accessory case there is not an oil path feeding the tach drive, looks to be splash lubrication. In this case there will not be a massive internal oil leak causing low oil pressure.
 
Tach drive

After some back & forth email with our very own Lyc guru Mahlon I left mine out.

Don Broussard
RV9 Rebuild in Progress
57 Pacer
 
Toobuilder said:
Reassembly of my 540 saw me delete not only the tach drive shaft, but one magneto idler gear and shaft assembly, swapped the fuel pump eccentric idler with the just deleted idler gear, deleted the fuel pump pushrod, and the vacuum pump drive gear, shaft and housing.

One needs to evaluate oil flow when eliminating parts in the accessory case. Many (like the idler gear and vaccum pump drive) are integral to the pressure lubrication path. Many people pull the vaccum pump shaft and leave the housing, not realizing they have just created a massive internal oil leak.
Click to expand...

As an EFII user I am doing something similar to my 540. I had planned to leave out the mag drive gears, the tach drive gear, vac drive, and of course the fuel pump plunger. You're saying the vac drive shaft is crucial to moving oil to all the other gears?
 
stringfellow said:
As an EFII user I am doing something similar to my 540. I had planned to leave out the mag drive gears, the tach drive gear, vac drive, and of course the fuel pump plunger. You're saying the vac drive shaft is crucial to moving oil to all the other gears?
Click to expand...

Depends on the gasket used. If you use the "cover plate" gasket which blocks the oil port at the accessory case then you are golden. I'm guessing you will delete the vac drive extension and just install a cover plate directly on the accy case which makes the gasket use moot. Where people run into trouble is removing the shaft, but leaving the extension. This leaves the 1/8 inch oil supply port to the shaft wide open and makes a massive internal leak. Block that leak with the gasket or a blank cover and you are fine.
 
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Toobuilder said:
Depends on the gasket used. If you use the "cover plate" gasket which blocks the oil port at the accessory case then you are golden. I'm guessing you will delete the vac drive extension and just install a cover plate directly on the accy case which makes the gasket use moot. Where people run into trouble is removing the shaft, but leaving the extension. This leaves the 1/8 inch oil supply port to the shaft wide open and makes a massive internal leak. Block that leak with the gasket or a blank cover and you are fine.
Click to expand...

Thank you. Always worried about stuff like this that falls into the "i don't know what I don't know" category.
 
Fuel pump drive?

Along the same lines, what about the fuel pump pushrod?

If the mechanical fuel pump is not going to be used, can the pushrod for the fuel pump be left in place, or does the accessory case need to come off and the rod removed?

Thanks
 
cajunwings said:
After some back & forth email with our very own Lyc guru Mahlon I left mine out.

Don Broussard
RV9 Rebuild in Progress
57 Pacer
Click to expand...

After a catastrophic engine O-320-D3G failure due to the tach drive (per Mahlon Russell) we agreed there's a potential failure mode due to the 'T'-pin fretting on a large bronze "washer". It may have been the destruction/autopsy of my Mattituck engine in '94 that gave Mahlon cause to offer sage advice on the tach drive.

5 electric tach experimentals, 8,000+ hours and one expensive failure = no more tach drives for me.
 
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