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Engine and gearbox mount dilemma
pitesy - 18/1/22 at 03:14 PM

Hi guys,

I am currently in the middle of preparing my FC3S rolling chassis to have an engine swapped in it.

The engine I have for it is out of an MX-5, the 1.8 vvt version. If I want to have the engine behind the steering rack, but still clearing the firewall, so I have to mount it with pretty tight clearances. Because of that I need mounts, that don't allow the engine moving too much and don't sag overtime (too much at least).

This lead me to a dilemma about engine and gearbox mounts.

I currently have a set of 95D (not shore A, but D, so bowling ball and hard hat hardness) engine and gearbox mounts meant for an M20 engine in an E30 (made by AKG in the US). They feature a straight through bolt, so they are pretty much solid when mounted. Which might give me problems with the "agricultural" 4 cylinder BP engine (these are meant for smooth inline 6's). People warned me about breaking stuff and bolts getting loose with the harmonics of the 4 cyl engine.

What is your take on engine and gearbox mounts? I have these ideas in mind:

- either get some softer polyurethane ones where the bolt on each side are not connected and allow some movement

- use the Jaguar V12 / Landy Defender / E30 M20 HD rubber /any other hard rubber mounts for both engine and gearbox

The car will only be used on track days, so extra NVH is not a concern, but bolts falling out and brackets snapping is. It is also important, that they don't allow the engine to move around too much.

Thanks a lot for your help!

Best regards all the way from Hungary
Stefan

jacko - 18/1/22 at 04:54 PM

Why not solid mount the engine and box by using suspension nylon mounts
G

pitesy - 18/1/22 at 05:03 PM

Thanks a lot for your input!

I've heard too many conflicting things about solid mounting. Some say it's okay and nothing will happen, others are convinced it will break crankshafts, gets all my bolts loose and will break unexpected things.

What I currently have are these:
https://www.akgmotorsport.com/product/motor-and-transmission-mount-set-for-bmw-e30-325-polyurethane-75d/

They are polyurethane, but a really hard one. Not sure how they compare to nylon?

theconrodkid - 18/1/22 at 05:28 PM

IMHO things like brackets will crack due to the vibes, land rover mounts are the bust to use in my opinion

RussH - 18/1/22 at 06:15 PM

I have very hard engine mount in my mx5 track car - everything rattles like crazy!

RWD Focus - 18/1/22 at 07:32 PM

Speak to someone GMT rubber, all my mounts come from those for every engineering application/project we ever do.


https://www.gmtrubber.com/

Hope this helps

Richard

nick205 - 19/1/22 at 09:05 AM

quote:
Originally posted by theconrodkid
IMHO things like brackets will crack due to the vibes, land rover mounts are the bust to use in my opinion



Agree - that is what I used on my MK Indy with a Ford Sierra Pinto engine and Type 9 gearbox. Very little engine movement and it did not give bad vibration in the car.

Mr Whippy - 19/1/22 at 01:48 PM

I tried solid mounting my pinto to my JBA Falcon, started it once and immediately changed my mind. Car sounded 10 times louder and vibrated like crazy. Best mounts are genuine diesel mounts for Landy or Transits, if your after comfort.

pitesy - 19/1/22 at 08:21 PM

Thanks a lot for all your replies! Let me just go one by one:

quote:
Originally posted by theconrodkid
IMHO things like brackets will crack due to the vibes, land rover mounts are the bust to use in my opinion


Indeed, vibrations cause these cracks. More and more people advise the land rover mounts. I am only unsure about how much engine movement I would have with those. Thank you!

quote:
Originally posted by RussH
I have very hard engine mount in my mx5 track car - everything rattles like crazy!


Do you maybe remember what kind of mounts they are? Thank you!

quote:
Originally posted by RWD Focus
Speak to someone GMT rubber, all my mounts come from those for every engineering application/project we ever do.


https://www.gmtrubber.com/

Hope this helps

Richard


Never heard of them before, thank you! I'll get in touch with them.

quote:
Originally posted by nick205
quote:
Originally posted by theconrodkid
IMHO things like brackets will crack due to the vibes, land rover mounts are the bust to use in my opinion



Agree - that is what I used on my MK Indy with a Ford Sierra Pinto engine and Type 9 gearbox. Very little engine movement and it did not give bad vibration in the car.


Thank you! It's good to hear the engine does not move much. Do you maybe know if the mounts sagged overtime?

quote:
Originally posted by Mr Whippy
I tried solid mounting my pinto to my JBA Falcon, started it once and immediately changed my mind. Car sounded 10 times louder and vibrated like crazy. Best mounts are genuine diesel mounts for Landy or Transits, if your after comfort.


Comfort is not a priority, as the car won't get used on the street, but I'd like avoid bolt backing out, or other issues. I will look into the landy mounts now, those got lots of votes already. Thank you!

nick205 - 20/1/22 at 08:28 AM

pitesy

The mounts didn't sag over the time I built and ran the car for 3,000 miles. They're pretty solid blocks of rubber! Don't know if MK Sportscars still supply them, but you could start looking on there website (I built my MK Indy 2003-2007 though).

pitesy - 20/1/22 at 03:15 PM

Thanks a lot Nick!

That is good news. I think I'll just buy those as engine and gearbox mounts as well. Leaving 10-15mm clearance everywhere should do the trick.

I was told with solid-ish and hard poly bushings you won't need more than 3-5mm (especially above the steering rack for example), but with rubber 10-15mm should work probably.