Author Topic: Engine to gearbox mounting  (Read 4406 times)

acmathom

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Engine to gearbox mounting
« on: October 16, 2014, 16:05:17 »
Dear Experts,
   I hope that is the right forum for my question.
   
   The AC engine in my car is connected to the gearbox via a mounting plate, which is attatched to the frame via a rubber mounting.
   
   It looks rather genuine for me and I have seen similar mountings in fellow AC prewar cars. As the plate is 5mm (sorry for the metric...), it increased the distance between the crankshaft and the bearing in the gearbox.
   Is there any experience about the need for this plate? It has been pointed out by a fellow expert, that it is not needed at all. The engine would than be supported only via the front mountings and the rear gearbox mounting. Will the engine be strong enough e.g. to cope with the flexing of the frame?
   
   Thanks and regards,
   Jurgen (ACmathom)

Robin A Woolmer

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Engine to gearbox mounting
« Reply #1 on: October 16, 2014, 16:45:26 »
Jurgen
   This looks like a post war engine, is it in a pre war chassis?, if post war then there was no plate to my knowledge between the engine & gearbox as the gearbox is supported with a rubber mount fitted to a support which straddles the chassis & underneath the gearbox!
   Pre War cars (PVT) did use a plate of this type to resist engine torsion & offer some support, the gearbox also had support dependant upon which one was used, e.g. the ENV box had a tube through the gearbox which met the chassis rails with a rubber type mounting, you appear to have a Post War Engine with a Moss Box probably in a PVT chassis, that would account for the plate.
   The gearbox bell housing flange is normally machined deeper to accommodate the plate thickness, if you remove the plate you will need to check the input shaft position to the rear of the crankshaft end as the input shaft has a bush into which the spigot on the crankshaft engages & runs, also you may need to make a spacer for the bell housing if the bell housing flange has been machined or the flange will not bolt flush with the rear of the engine flange so may crack the flange!

acmathom

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Engine to gearbox mounting
« Reply #2 on: October 16, 2014, 17:02:38 »
Hi Robin,
   
   that´s right: Postwar engine in the PVT chassis. The bush in the gearbox shaft is only used the first few millimeters when the plate is attached, so plenty of space left for the spigot. In order to avoid the machining of the bell housing I might need another support or a plate of less thickness. I can nderstand now, that some support might be helpful!?
   
   Jurgen

Robin A Woolmer

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Engine to gearbox mounting
« Reply #3 on: October 16, 2014, 18:25:50 »
Jurgen
   You may not need to machine the bell housing flange if the register will just mate with the engine flange as the post war bell housing does, the Moss gearbox or the bell housing should have a bottom face so a support bracket could be fitted across with a rubber mount between as per post war saloons.
   Just one point about the front engine mount is this similar to the PVT mounting yoke which allows the engine to move relative to the chassis when the chassis twists? or do you have another form of flexible mounting for the post war engine side mounts?
   It is important that the engine is not stressed by chassis twist!
   Robin

acmathom

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Engine to gearbox mounting
« Reply #4 on: October 17, 2014, 23:01:16 »
Robin,
   
   thanks for the advice. I have taken out the engine again today. I have taken a few pictures. The plate will also be removed and I now have to think about making a bracket from the bushes used for the plate to the bellhousing of the gearbox. Is there anyone out there who could provide a picture of the bracket used in the saloon? I would suspect to be different from the one used in the Ace (picture below).
   
   Front mounting of the postwar engine in the PVT chassis:
   
   
   
   Engine has been taken out again:
   
   
   Plate still in position to support the gearbox:
   
   
   Bracket from a spare Moss gearbox, reported to be from an Ace:
   
   
   Bracket to connect the bellhousing to the fixing points for the plate:
   
   
   Regards,
   Jurgen

Robin A Woolmer

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Engine to gearbox mounting
« Reply #5 on: October 18, 2014, 10:43:55 »
Jurgen
   I am a little concerned with your front engine mounts, they appear to be a rubber bush sandwiched between the underside of the engine mount & the chassis bracket with a bolt through, if this is so there will be a small movement to accommodate chassis twist.
    Can I suggest you consider the type of mounts used on the Post War Saloons where there is an isolating bush which allows a good degree of flex without stressing the engine block.
   The ideal front mount for this type of chassis would be the original central mount which allows the chassis to twist with virtually no stress on the block!
   I presume the post war saloon chassis was made with side mount engine mounts was to allow the engine to be positioned more forward to offer more cabin room so using the rubber bonded mounts!
   The AC Ace has similar side mounts but with a narrower chassis & different suspension so not causing so much chassis twist.
   Please let us know if you feel there is enough travel in the mounts to accommodate any chassis twist?

acmathom

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Engine to gearbox mounting
« Reply #6 on: October 25, 2014, 19:17:10 »
I understand your point! I have seen the original central mount at another car and this seems to be more appropriate to cope with lateral chassis flex. Might there be someone who could provide a picture of the engine mounts in the saloon?