S

Sid Lambert

Well Known Member
I'm in the process of rebuilding my O-320 and have a question for you guys..

Why do I need to put the tach drive back in the engine? I have 1 EI and 1 mag but the RPM is read from the P-lead on the mag. It's always just had a cover over it. Seems like just something else that can break.
 
I am new to aircraft engines, but have automotive experience. There appears to be no reason why the tach drive be installed, assuming you safety the cap. Without the tach drive and it's seal, you could theoretically lose oil quickly from that opening. With the tach drive and seal installed, a missing cap would cause a slow leak.

I will be installing it on my O-320 rebuild just in case I need it in the future or possibly sell the engine for an upgrade.

Larry
 
lr172 said:
With the tach drive and seal installed, a missing cap would cause a slow leak.
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Actually the cap is only a dust cover. With the tach drive and seal installed, there should be no leaks at all.
 
As usual, Mel is correct!

You need both the tack drive AND the cap installed.

A friend left out the drive and just put the cap on and it turns out the Lycomings have an oil squirter that lubricates the tach drive. Without that drive in place, it just squirts oil out the breather tube.
 
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Oil passage to tach drive

I've looked and looked for a oil passage or oil squirter on the tach drive shaft and can't find one on my O-320. Anyone know where it is?
Thanks
 
I am rebuilding an O-320 right now. There is definitely no squirter on the accy case. My block just came back from the shop yesterday. Next week I'll look and tell you if there is one. However my tach shaft if shielded to avoid liquid oil getting to the breather (i.e. getting splashed from the gears.

Larry
 
Tach Drive

I sent a pm to one our very own & well known forum engine experts and he said there is no squirter unless the case had been modified in some way. He has seen the oil separator flange left out and that caused oil loss out the breather. He also has seen problems caused by running the engine with the tach drive installed but without a tach cable being connected. I did not install the tach drive. I cut a round gasket from some red silicone baffle seal material and covered the drive with the store bought metal cap.


Don B
RV 9 Rebuild in Progress.
 
"Squirter" may be the wrong word. Oil may be splashing off one of the gears in there and deflected off the tach drive shaft. Either way, you want that shaft in there on the O-360's. The O-320's may be different.

If you leave it out and it becomes an issue, your spotters will see it just about the time you rotate. You can always add it later, but it is a pain to do then because you have to drop the sump to get the accessory case off.

As Mel mentioned, regardless of what you do, you will want to install a cover over the tach drive.
 
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cajunwings said:
I sent a pm to one our very own & well known forum engine experts ... He has seen the oil separator flange left out and that caused oil loss out the breather...

Don B
RV 9 Rebuild in Progress.
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I checked with my friend who had this problem and just like my engine, the oil separator flange was pressed into the accessory case prior to assembly. So yes, it was in place, along with the tach cover. The only part he left out was the tach drive shaft.

If you have a forward breather tube like my O-290 had, then this isn't an issue.
 
cajunwings said:
He also has seen problems caused by running the engine with the tach drive installed but without a tach cable being connected.
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Did he mention what kinds of problems? I also will not be installing a tach cable and wonder if this is just oil leaking without a cap or possibly the shaft having runout due to no support from the tach cable.




cajunwings said:
...and covered the drive with the store bought metal cap.
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Where did you find one? I have struggled to find anything in 7/8-18 thread. I was thinking of a silicone rubber cap if I installed the tach drive with seal, but would want something threaded and safety'ed if I left the tach drive out.

Thanks,

Larry
 
I've seen many engines running for years, mine included, with tach drive installed and no tach cable.

Never seen a problem with this set-up.
 
Tach drive

This is the reply from our forum engine guy I got in a pm.

[No problem leaving the tach T drive out. As a matter of fact some times when you don't hook a load up to that drive it allows the roll pin portion of the T drive to dig into the bronze bushing in the end of the cam. I have seen it actually destroy the bushing and make a lot of metal as it cuts into the bushing. I could never figure out why that happened in some instances and not all where the tack drive wasn't being used. If it were mine and I knew I was never going to use the tach drive I would definitely leave the t drive out. There are no oilers as one poster suggested unless they made some sort of Mod to get an oiler. The only time I ever saw the oil get thrown out the breather was when the slinger (on the accessory housing or cam depending on the age of the engine) wasn't installed properly.]


Based on that I made sure the slinger was secure and left the drive out. Electronics International has the caps as do other vendors.

Like everything else YMMV.

Don B
RV 9 Rebuild in Progress
 
cajunwings said:
This is the reply from our forum engine guy I got in a pm.

[No problem leaving the tach T drive out. As a matter of fact some times when you don't hook a load up to that drive it allows the roll pin portion of the T drive to dig into the bronze bushing in the end of the cam. I have seen it actually destroy the bushing and make a lot of metal as it cuts into the bushing. I could never figure out why that happened in some instances and not all where the tack drive wasn't being used. If it were mine and I knew I was never going to use the tach drive I would definitely leave the t drive out. There are no oilers as one poster suggested unless they made some sort of Mod to get an oiler. The only time I ever saw the oil get thrown out the breather was when the slinger (on the accessory housing or cam depending on the age of the engine) wasn't installed properly.]
Based on that I made sure the slinger was secure and left the drive out. Electronics International has the caps as do other vendors.

Like everything else YMMV.

Don B
RV 9 Rebuild in Progress
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I had exactly this happen on an O-320-D3G. A post mortem by Mahlon Russell and Phil Haponic at Mattituck pointed to the unloaded (mag driven electric tach) T-drive oscillating causing the bronze bushing to fail and break into pieces. The T-drive was left out during the subsequent overhaul with the admonition that the engine could never use a mechanical tach or a tach signal generator.

The issue was diagnosed through oil analysis and oil suction screen inspection.

Dick Kreidel
 
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