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viperdoc(at)mindspring.co
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 Posted: Tue May 28, 2013 11:21 am Post subject: Tach drive |
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For that matter, they all share a spline drive cog.
Doc
Sent from my iPad
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mark.bitterlich(at)navy.m
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| Posted: Tue May 28, 2013 11:51 am Post subject: Tach drive |
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Yes Doc, and that is what I was trying to emphasize. Tell me exactly
which one of those spline cogs is attached to the Tach Drive! It's
important to know. The Tach Drive is not stand-alone, it is part of an
overall gear mechanism as your picture shows clearly. It does not
matter where the actual hole is on the case, what is important for the
average engine owner to understand is that the Tach Drive is part of the
whole accessory drive MECHANISM, and is a CRITICAL cog.
If you pull the Tach Drive Cover Plate clear out of the engine, you can
easily cause the Air Start Distributor to come out of time. This has
actually happened when some folks converted their Tach Drive systems
over to the P-1000 Tach by Horizon Instruments, that uses the Mag P-Lead
wire to determine engine RPM. They first pulled the Tach Drive itself
out, and then they decided to pull the next cover plate off in order to
make a blank off plate. Well, they went a tad bit too far in the "pull
and remove" phase, and managed to yank out the gear that goes with into
that mechanism you have a picture of, which allowed everything to come
out of time.
Give it a try and see what happens.  I would rather not. I saw it
happen after the fact, and had to re-time the Air Start Distributor for
the gent, which some folks claim is easy. I guess I am not as good as
they are, because for me it was a real task.
I am not an M-14 engine expert. Most of what I have learned has been
due to the mistakes made by myself and others. Some of those mistakes
have ruined entire engines, luckily not by me for the Grace of God! I
usually pass those lessons on via the Yak List. This is one of those
times.
Take care,
Mark
--
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viperdoc(at)mindspring.co
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| Posted: Tue May 28, 2013 5:03 pm Post subject: Tach drive |
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Mark,
Unfortunately I'm reading this after I have left the hanger. Tomorrow if I can remember with all the crap going on in my life right now I will try to get you a picture that shows exactly how the two interface in the accessory case. I will try to find the shipping cover that came with my new engine. It like the tach driver has a shaft that fits in the accessory port most likely to keep the pinion gear from slipping into the accessory case.
If you look at that domed area behind the two splined gears that you see at an angle , the gears that drive the octopus and the tach drive.
It has been a year since I had the thing apart. The memory has faded a little on this.
Doc
Sent from my iPad
On May 28, 2013, at 2:48 PM, "Bitterlich, Mark G CIV NAVAIR, WD" <mark.bitterlich(at)navy.mil> wrote:
[quote]
Yes Doc, and that is what I was trying to emphasize. Tell me exactly
which one of those spline cogs is attached to the Tach Drive! It's
important to know. The Tach Drive is not stand-alone, it is part of an
overall gear mechanism as your picture shows clearly. It does not
matter where the actual hole is on the case, what is important for the
average engine owner to understand is that the Tach Drive is part of the
whole accessory drive MECHANISM, and is a CRITICAL cog.
If you pull the Tach Drive Cover Plate clear out of the engine, you can
easily cause the Air Start Distributor to come out of time. This has
actually happened when some folks converted their Tach Drive systems
over to the P-1000 Tach by Horizon Instruments, that uses the Mag P-Lead
wire to determine engine RPM. They first pulled the Tach Drive itself
out, and then they decided to pull the next cover plate off in order to
make a blank off plate. Well, they went a tad bit too far in the "pull
and remove" phase, and managed to yank out the gear that goes with into
that mechanism you have a picture of, which allowed everything to come
out of time.
Give it a try and see what happens. I would rather not. I saw it
happen after the fact, and had to re-time the Air Start Distributor for
the gent, which some folks claim is easy. I guess I am not as good as
they are, because for me it was a real task.
I am not an M-14 engine expert. Most of what I have learned has been
due to the mistakes made by myself and others. Some of those mistakes
have ruined entire engines, luckily not by me for the Grace of God! I
usually pass those lessons on via the Yak List. This is one of those
times.
Take care,
Mark
--
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Robin Hou
Joined: 19 Jan 2017
Posts: 15
Location: El Monte, CA
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| Posted: Fri Jul 07, 2023 6:43 pm Post subject: Re: Tach drive |
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Mark,
I am installing a M-14p engine that the tach drive had previously been removed then put back without properly engaging the air distributor gear. Is it possible to re-engage the air distributor gear with the tach drive gear without removing the accessory case? If so, can you share your experience on how to do that?
Thanks in advance,
Robin Hou
[quote="mark.bitterlich(at)navy.m"]Yes Doc, and that is what I was trying to emphasize. Tell me exactly
which one of those spline cogs is attached to the Tach Drive! It's
important to know. The Tach Drive is not stand-alone, it is part of an
overall gear mechanism as your picture shows clearly. It does not
matter where the actual hole is on the case, what is important for the
average engine owner to understand is that the Tach Drive is part of the
whole accessory drive MECHANISM, and is a CRITICAL cog.
If you pull the Tach Drive Cover Plate clear out of the engine, you can
easily cause the Air Start Distributor to come out of time. This has
actually happened when some folks converted their Tach Drive systems
over to the P-1000 Tach by Horizon Instruments, that uses the Mag P-Lead
wire to determine engine RPM. They first pulled the Tach Drive itself
out, and then they decided to pull the next cover plate off in order to
make a blank off plate. Well, they went a tad bit too far in the "pull
and remove" phase, and managed to yank out the gear that goes with into
that mechanism you have a picture of, which allowed everything to come
out of time.
Give it a try and see what happens. I would rather not. I saw it
happen after the fact, and had to re-time the Air Start Distributor for
the gent, which some folks claim is easy. I guess I am not as good as
they are, because for me it was a real task.
I am not an M-14 engine expert. Most of what I have learned has been
due to the mistakes made by myself and others. Some of those mistakes
have ruined entire engines, luckily not by me for the Grace of God! I
usually pass those lessons on via the Yak List. This is one of those
times.
Take care,
Mark
--[/quote]
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GeorgeCoy
Joined: 02 Dec 2010
Posts: 310
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| Posted: Sat Jul 08, 2023 6:10 am Post subject: Tach drive |
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My 2 cents. If you pull the inner pat of the Russian tach drive, There is a
good chance the mating bevel gear has dropped down. We had a client with an
almost new TW do this and got it started. The bevel gear chewed trough
another shaft and fille the engine with mental.
If it is reinstalled already, you can check the air start timing to
confirm that it did not move.
George Coy
--
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Robin Hou
Joined: 19 Jan 2017
Posts: 15
Location: El Monte, CA
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| Posted: Sun Jul 09, 2023 10:25 am Post subject: Re: Tach drive |
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Hi George,
Thanks for your comment. Unfortunately the tach drive gear must have been pulled before I purchased the engine many years ago. Not knowing that, coupled with the good luck (or bad luck?) I was able to place the prop on the only cylinder that was getting the start air and run this new engine for 10 min during which time the air distributor gear badly damaged the oil pump drive shaft. I wish the manual called for checking air distributor timing verification as a part of its de-preservation process but, in my case, it is too late now.
So my original question is not relevant anymore because I will send my engine to a shop for repair.
Best regards,
Robin
[quote="GeorgeCoy"]My 2 cents. If you pull the inner pat of the Russian tach drive, There is a
good chance the mating bevel gear has dropped down. We had a client with an
almost new TW do this and got it started. The bevel gear chewed trough
another shaft and fille the engine with mental.
If it is reinstalled already, you can check the air start timing to
confirm that it did not move.
George Coy
--[/quote]
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