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MG MGB Technical - Engine mount

Does anyone know the purpose of the plate AHH6992 which is fitted to the left side engine mount?

Mick

M F Anderson

Mick
I 'think' I can help you with that-
I believe it's a leftover/flowon from the MGA
It's called a rebound plate and stops the lh front corner of the oilpan from bottoming out on the crossmember during rough idle and/or during deceleration

cheers
willy
William Revit

It's described as a shim or packing, I've always imagined it was to cope with tolerances on the chassis rails with the angled surfaces to allow the bolt holes to line up as some suppliers state 'as required'. However others show '1', '2', or don't list it for the MGB even by a major suppler such as Brown & Gammons. Could well be as Willy.
paulh4

Willy, no it isnt the rebound plate, that has an angle in it and it stops the engine moving forward under braking. Picture attached.

It is just a packing piece sometime used if there is a gap between the rubber engine mount and the crossmember.

Colin

Colin Parkinson

Nah, that is an engine restraint bracket to limit forward movement

The plate Mick is refering to is a packer under the lh engine mount-Paul is probably correct in saying it is a packer to adjust for out of spec body brackets, but I have regularly heard of them being called rebound shims and if you leave one out of an mga that has one fitted the oil pan will definitely whack the crossmember on rebound

https://www.ebay.com.au/itm/RECOIL-BRACKET-PLATE-LH-FRONT-ENGINE-MOUNT-MGA-MGB-58-67-AHH6992-413-075-USED-/264223313505
William Revit

There has been some confusion regarding the item being discussed.
Willy is mentioning the correct item but still the use is not clear.
If it is to raise the engine higher to stop the sump hitting the crossmember why on only the left side? Why not on the right side also? Why not more than one (“as required”)?
The factory Service Parts List (attached) specifies one only and on the left side,
Not the varying statements by current current suppliers.
It is item 3 part number AHH6992.

Mick

M F Anderson

On acceleration it's the left-side of the engine that tries to lift (as I noticed when that side mount on my V8 parted) and will compress the mount on deceleration. On that basis what Willy would fit, but it raises the question of why the same couldn't happen to the right-hand side on acceleration. And also why both sides wouldn't do over bump large enough to shock the car upwards, which would tend to leave the engine behind, or on landing from a jump.

Just fit it and forget it :o)
paulh4

Mick
Found this on another forum,
one bloke's view but---
"
The packing plates were used to correct alignment of the welded engine mountings.

The number varied from shell to shell. I've seen anywhere from none to three packing plates on cars that I've worked on. Just as the number of shims on the steering racks, there is no right or wrong setup. I've seen shims on both the right and left side mount, but usually it's just the left hand.

When installing the engine, check that the mounts line up accurately and that the engine does not appear to sag. If when you lower the engine, the mounts sit too low on the body bracket, it's an indication that a shim should be used or the mounting rubber is going to be stretched which will cause premature failure.

As Terry noted typically you see the shims on the left hand side of LHD cars as the clearance between the manifold and steering column is critical. If the welded engine mountings were off, the engine would hit the column. Installing shims raises that side and gives clearance.
"
William Revit

This thread was discussed between 29/01/2021 and 30/01/2021

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