Engine and gearbox mount dilemma

[pitesy]

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 bolts on each side are not connected (and are not straight through) 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


 

[legend]

Retropower had some through bolt type mounts made up in a softer rubber that they used on Gordon Murray's car. I think they were planning on selling them too, Might be worth a call

retropower.co.uk/contact/

[biturbo228]

Ford Cortina/Escort Mk1 leaf spring front eye bushes can be had in poly (part number SPF0935K) and fit snugly inside a 50.8mm diameter 2mm wall tube. The crush tube in the middle is 1/2" so M12 bolts fit nicely through it. I picked those as there's a bit more material between the crush tube and the outer edge than is typical of most suspension bushes, so thought it would provide a bit more cushioning.

They've made good engine mounts for the X1/9 so far! Little increase in NVH over the rubber originals, but nothing particularly bad and no bolts backing out or anything nasty like that.

[ChasR]

Be aware that there is more to designing a bush than just the shore rating.

This is the difference between companies like FloFlex and your top end companies like SuperFlex & SuperPro. One will use cheap and more plastic/nylon based poly which will deform quicker than when you fitted it, as well as causing more NVH issues. The other will have R&D and other things put into them to make them right. That takes time, and time is money to a company. That said, it seems Poly bushes don't always work for engine mounts.

SuperPro don't seem to sell many, only inserts.

In your case, I'd be tempted to use the MX-5 mounts up front if possibly, with some BMW bobbin gearbox mounts at the rear. But alot of this depends on how things are secured already. Isn't the gearbox attached to the main rail that connects the gearbox and prop together on an MX-5 and also an RX-7?

[giuliettaevo]

We have been using generic vibration dampers for ages. I have my 5 pot jtd engine resting on 2 of those. 75mm diameter, 45mm high, 57shore, type A with 2x threaded M12 Rod.

[ferny]

I ran solid mounts in the Herald for a few years. Didn't cause any issues.

[goldnrust]

Jan 18, 2022 17:39:00 GMT ChasR said:

Isn't the gearbox attached to the main rail that connects the gearbox and prop together on an MX-5 and also an RX-7?

Mx5 and FD use the PPF (power plant frame) as you describe. FC and FB Rx7 a use a traditional gearbox mount.

You can use the tail housing from an NA FC gearbox on the 5 speed mx5 gearbox to allow you to use the OEM gearbox mount if that saves hassle. That might not work with your engine positioning.

I did the reverse if this when fitting a 13b from and FC into my mx5 many years ago.

Would it be worth considering some sump mods to help increase clearance rather than rock hard engine mounts?

[ChasR]

Jan 18, 2022 20:51:09 GMT ferny said:

I ran solid mounts in the Herald for a few years. Didn't cause any issues.

Conversely, a friend of mine ran Group A solid mounts on his Mk2 Golf GTi 16v with a Brian Rickett Motorsport engine conversion (Bored out to 2.0). Basically, a solidly mounted engine

He tried everything
-Nylocs
-Loctite
-A combination of the two

It shook itself to bits.

What annoyed him was coming back from the Nurburgring. About 100 miles way, the gearbox mount decided it wanted to come loose. On VW Motorsport mounts, the issue of the mounts undoing themselves went away.

Solid mounts work on some cars, but not on others, or at least, they require regular checking.

[pitesy]

Wow, thanks a lot everyone! I wasn't expecting that many reactions.

Let me just go one by one:

Jan 18, 2022 15:11:34 GMT legend said:

Retropower had some through bolt type mounts made up in a softer rubber that they used on Gordon Murray's car. I think they were planning on selling them too, Might be worth a call

retropower.co.uk/contact/

I'll get in touch with them, thank you!

Jan 18, 2022 16:10:25 GMT biturbo228 said:

Ford Cortina/Escort Mk1 leaf spring front eye bushes can be had in poly (part number SPF0935K) and fit snugly inside a 50.8mm diameter 2mm wall tube. The crush tube in the middle is 1/2" so M12 bolts fit nicely through it. I picked those as there's a bit more material between the crush tube and the outer edge than is typical of most suspension bushes, so thought it would provide a bit more cushioning.

They've made good engine mounts for the X1/9 so far! Little increase in NVH over the rubber originals, but nothing particularly bad and no bolts backing out or anything nasty like that.

That does look like a great solution! Sadly I am not a great fabricator, I can only do some basic stuff. I also agreed on with a welder friend of mine, that I only need to tack my mounts together so they don't fall apart, he'll do the welding for me.

Thank you!

Jan 18, 2022 17:39:00 GMT ChasR said:

Be aware that there is more to designing a bush than just the shore rating.

This is the difference between companies like FloFlex and your top end companies like SuperFlex & SuperPro. One will use cheap and more plastic/nylon based poly which will deform quicker than when you fitted it, as well as causing more NVH issues. The other will have R&D and other things put into them to make them right. That takes time, and time is money to a company. That said, it seems Poly bushes don't always work for engine mounts.

SuperPro don't seem to sell many, only inserts.

In your case, I'd be tempted to use the MX-5 mounts up front if possibly, with some BMW bobbin gearbox mounts at the rear. But alot of this depends on how things are secured already. Isn't the gearbox attached to the main rail that connects the gearbox and prop together on an MX-5 and also an RX-7?

I am with you on that one. I wanted to avoid the cheap/china stuff, as I'd like to do it once, but do it right for the first time.
Below someone mentioned it, but on the FC the mounts are normal mounts, no PPF gladly.

Regarding the gearbox mount: I wanted to create another thread looking for ideas, as I've seen people mounting MX-5 engine in other cars.

Thank you!

Jan 18, 2022 19:25:53 GMT giuliettaevo said:

We have been using generic vibration dampers for ages. I have my 5 pot jtd engine resting on 2 of those. 75mm diameter, 45mm high, 57shore, type A with 2x threaded M12 Rod.

I'll have to google vibration dampeners, in this context I haven't heard of them yet. Thank you!

Jan 18, 2022 20:51:09 GMT ferny said:

I ran solid mounts in the Herald for a few years. Didn't cause any issues.

Thank you! I was able to talk to an "internet friend" of mine running the same swap. FC chassis, 1.6 MX-5 engine with a stupid big turbo. His engines mounts are steel (no rubber or poly at all, completely solid), gearbox mount is nylon/delrin, so also solid. He said ha never had issues with bolts backing out in the past 5+ years he drifted his car, or breaking stuff. Hmm.. Other on various MX-5 forums say the complete opposite.

Jan 18, 2022 22:40:42 GMT goldnrust said:

Jan 18, 2022 17:39:00 GMT ChasR said:

Isn't the gearbox attached to the main rail that connects the gearbox and prop together on an MX-5 and also an RX-7?

Mx5 and FD use the PPF (power plant frame) as you describe. FC and FB Rx7 a use a traditional gearbox mount.

You can use the tail housing from an NA FC gearbox on the 5 speed mx5 gearbox to allow you to use the OEM gearbox mount if that saves hassle. That might not work with your engine positioning.

I did the reverse if this when fitting a 13b from and FC into my mx5 many years ago.

Would it be worth considering some sump mods to help increase clearance rather than rock hard engine mounts?

Thank you! I looked into that too, but there are two things about it:

1. If you mate the gearboxes, you'll be limited to the MX-5 5 speed gearboxes. Eventually I will go turbo, so a 6 speed will be on order. Or even an FC gearbox with an adapter, but that's not in the future.

2. With the gearbox in the stock location the engine quite far forward and high up (unless you tilt it, but it won't match the pinion angle then), there's about another ~10cm you can move it back and at least 5cm to lower it. Also in that position because of the vvt solenoid on the top the bonnet would not shut. You can get subframe spacers, but I'd like to avoid using them too.

I will hang the engine in there one more time when I can finally go the garage and will poke around, if the clearance can be increased somehow. It's tight in front of the sump, where the oil pickup starts, but I'll check once again before cutting it up. I will also substitute the bulky pipe fitting on the back of the for the vvt oil supply for a regular braided line, so more clearance again to move the engine back.

Jan 18, 2022 23:57:13 GMT ChasR said:

Jan 18, 2022 20:51:09 GMT ferny said:

I ran solid mounts in the Herald for a few years. Didn't cause any issues.

Conversely, a friend of mine ran Group A solid mounts on his Mk2 Golf GTi 16v with a Brian Rickett Motorsport engine conversion (Bored out to 2.0). Basically, a solidly mounted engine

He tried everything
-Nylocs
-Loctite
-A combination of the two

It shook itself to bits.

What annoyed him was coming back from the Nurburgring. About 100 miles way, the gearbox mount decided it wanted to come loose. On VW Motorsport mounts, the issue of the mounts undoing themselves went away.

Solid mounts work on some cars, but not on others, or at least, they require regular checking.

Thank you! That is what I am also afraid of. The above scenario must have been a pain in the butt, would like to avoid it at all cost. 4 cylinders are not that well balanced by nature, as lets say an inline 6.

[giuliettaevo]

On bmw's e36s some people mount the engine solid. Resulting in sheared off mounting ears on the subframe.. for which there is a strengthening set available. After mounting that they break the aluminium enginemounts...

There is a reason for the flexibility.

Try to match the motormounts and gearboxmounts in shore-rating for the harshness. Equally hard rubbers is preferred.

[kevins]

You really do need a bit of compliance or a really strong set up, otherwise the engine mount system becomes part of the vehicle structure and is also trying to resist the vehicle twist, if you are not worried about noise and vibration cheap poly bushes would be fine, where the better ones score is where you want good vibration absorption and long life, the cheap ones are usually way to stiff for this.

[pitesy]

Jan 19, 2022 22:41:25 GMT giuliettaevo said:

On bmw's e36s some people mount the engine solid. Resulting in sheared off mounting ears on the subframe.. for which there is a strengthening set available. After mounting that they break the aluminium enginemounts...

There is a reason for the flexibility.

Try to match the motormounts and gearboxmounts in shore-rating for the harshness. Equally hard rubbers is preferred.

Thank you! Indeed, I was afraid of that as well. Regarding rubber mounts: I am eyeing with the Land Rover rubber mounts, they are supposed to be quite hard for rubber, but still retain some compliance.

Jan 20, 2022 10:25:04 GMT kevins said:

You really do need a bit of compliance or a really strong set up, otherwise the engine mount system becomes part of the vehicle structure and is also trying to resist the vehicle twist, if you are not worried about noise and vibration cheap poly bushes would be fine, where the better ones score is where you want good vibration absorption and long life, the cheap ones are usually way to stiff for this.

Thank you! After making some research and getting good advices, like yours I'm also leaning towards non solid mounts. It will either be the Land Rover mounts, or if I can find some good poly ones, then those. Some vibration and noise is okay though, but I won't cheap out if I go poly.