Replacing conical engine mounts in-situ

[Mark Albery]

I've decided to 'bite the bullet' and replace the old hardened engine mount bushes in my RV-4 with a set of J-1552 Lord mounts in place of the old 71032 Lycoming ones.

I'm told that they are dimensionally equivalent, so no bolt length etc changes.

My plan is to support the engine, loosen all the mount bolts and then replace the bushes one at a time without removing the engine.
Has anyone tried doing it this way or anticipates any problems with my plan?

[chrisbryanolsen]

Mark,
I need to do the same thing, so let me know how it goes.

[DougJ]

Mark, aren't the 71032 and equivalent for conical and the J-1552 for dynafocal mounts?

I have a conical mount O-320 and I'm planning to buy a new set of Lycoming bushings, Spruce PN 05-08074, or the "HOMEBUILDERS CONICAL LYCOMING ENGINE MOUNT BUSHINGS" Spruce PN 08-00662. Both of those are 71032 equivalent.

I will utilize an engine hoise and try to replace them with as little additional teardown as possible.

[Mark Albery]

Doug,

AIUI the J-1552 is a higher performance, and more expensive, direct replacement for the conical rubber bushings for conical mount engines.
My engine was originally from a Tri-Pacer.
I think that the mounts should be a lot easier to replace than on a Dynafocal mount as the bolts are all parllel.

[vic syracuse]

I just replaced these on an RV-6 and used the J-6230-1 Lord Mounts. It does require a little bit of work, but it is easier than the Dynafocal mounts.

Vic

[Mark Albery]

Vic,

I think that those mounts are the eccentric ones that need an indexing pin to be added on to the mounting pads of the engine frame.

My understanding is that the J-1552 is very similar but concentric, so doesn't need indexing and is a drop-in replacement for the 71032.

I think Van's sell the J-6230-1 as "EA CON VIBRATION ISO".

[vic syracuse]

You are right, but they were very easy to clock.

[Toobuilder]

I've done several sets of both conical and dynafocal mounts "in situ". Do two at a time (top or bottom) with the engine supported by a hoist at the prop. Raising or lowering will open plenty of gap to slip the mounts in and out. Just watch for control cables or hard interference against the engine mount, exhaust, etc. usually, there is enough flex/clearance to open quite a gap.

The hardest part, really, is getting the cotter pin installed in the upper left side without screwing up the pushrod tube.

[vic syracuse]

Yes, it is very easy to damage that pushrod tube if one is not careful. Turning the bolt around seems to provide a lot more clearance.

Vic

[Mark Albery]

I've just received the j-1552 Lord mounts.

They seem to differ from the Lycoming 71032 bushes in that there is a 3/4" counterbore around the 1/2" bolt hole.

I presume that is for an internal spacer that I don't have with the Lycoming bushes.

Does anyone know if that is correct or have a source and part number for the spacer?

Also, if there is a metal spacer then I presume the torque requirement would be more than the 40-60 in-lb that the Lycoming bush uses.

Any pointers would be appreciated.