I am putting a late model motor in to a Mk1, and have been advised not to solid mount the motor, but to leave either the front or back with some play I was intending on making all the mounts 100% solid, anyone here done that? Any fatigue issues I should be aware of? Car is purely race, but it will hit curbs at 100mph I was also adding a bottom strut brace that bolted to the gear box, again this is rigid, so there would effectively be three bottom mounts and 2 sideways. Due to the class rules mounting the bottom strut brace to the gearbox is pretty much essential, although I could probably work a flex bush in there, it would make my life harder than it needs to be! Anyone with experience and problems that have arisen?
Tried this in a mk1 eons ago. The whole car will buzz, bolts will slacken, it will be tiring to drive. Shock will crack mounts, especially the rear gearbox mount, in my experience. If you can find VW motorsport mk1 bushes, ideal. These are just a little bit softer than solid. My tuppenth. Still have the solid mounts 'in stock' Jon
aye not worth it I made one in the 90's and took it off after a day or two was like being in a beer can with a wasp i used shore 90 equivalent polly even with voids cut in it it was still to stiff
Vibration and harshness are just not an issue, I use loctite on just about everything, and our longest races are 30 minutes so fatigue is not a problem. My existing car has them but it is a V6, so inherently smoother and the way the mounts support the motor is inherently different Interested in the rear mount cracking though In your opinion would solids on the rest with a poly on the back provide enough give to assist with that, I suspect a commercially available rear would be closer to 60 durometer than 90. I do have some round billet 95 that I could use for other mounts, but that is pretty much rock hard anyway What about the thought of the left and right are solid but the front, rear and new bottom had movement
I'm sort of on the other side of the fence on this. I run solid mounts on the Hill climb car no problems but I do have strengthened mounts and rose jointed top and bottom mid mounts (The top one is totally bespoke). Motorbikes all use solid mounts with no problems and big power (but low weight it has to be said), so do F1, F3 etc. and I'm sure BTCC and top circuit cars do. The car is a bit harsh with solid mounts it is true, but for short events like hills and sprints its fine, maybe it could be tiring on a circuit or a rally and as Jon says the strain could break things. The plus side is the exhaust will not break, you can run tight clearances on carbs/throttlebodies/belts etc. without worry. Escort GP4 mounts are a good source of HD engine mounts with some sort of vibration reduction form Rally design or GP4fabrication, for example Either bespoke using a Vauxhall XE conversion kit or use std mounts, take out existing rubber and fabricate up a steel holder or press in a turned aluminium one. I've got both types in the workshop, the aluminium version looks nice, the steel is lighter. Also lets you move the engine about in the bay a bit if you so wish when making! Wouldn't consider either for a road car I don't think, Polybushes etc. are bad enough! Vibratech stuff seems ok, but quite expensive.
I'm talking about MK1's here, the later stuff gets more complicated. I used Vibratech on the MK2 and its fine. although I'd still solid mount motor and subframe for hills and sprints if that is what I used it for.
Rob, I'm guessing two reasons. One passenger comfort and two long term reliability. Even though yours is at the extreme competition end, the radical has a road legal side so passenger comfort must have some small box to tick. I'd imagine more likely for long term reliability though. You can feel in my hillclimb car that some of the vibration is that nasty high frequency type that fractures metal parts. On short bursts not an issue but a whole days rallying........ yeah, could see that being an issue. Clearly doesn't need much to damp them out, or reduce the shock that little bit. You have to assume they put them there for a reason that showed up at some point if the bike manufacturers don't consider the need to use them. Interesting.
I use the Escort GP4 type inserts Tony has mentioned on my racecar, front and rear from JMR (Mr Hillclimber in here) and fabricated both the side mounts from scratch.
Sr8 is really an endurance racer, so it will be for reliability I think, multi hour races at high rpm will take their toll on parts. This is obviously an issue as many fasteners are knuts, nylocks, or lock wired. Every drain plug is lockwired. Vibration sensitive electrical parts are all rubber mounted. For hillclimbs with a trailered car its probably not an issue due to the short run times. Anything else, personally, I would use some rubber in there, even if its hard and theres not much of it.
Anything for rally or road I wouldn't even be asking. But an average 2 day meeting we probably drive for a total of an hour, then there is 2 months of prep for the next one! I have a bit if the 95 Durometer poly, which I bought to put in the rear beam mount so I will use that on the round mounts, CAMS (Australian MSA equivalent) consider anything harder than 95 to no longer be elastomeric so it is pretty hard stuff and turns up in the lathe if you keep it cool I could probably leave the rear standard with the new bottom gearbox mount, now I need to work out the best way to make that... I suppose some of the shelf cotton reels joining the strut brace
I made the rear one on mine with a rear beam poly bush. The gearbox bracket was bought off the web but it's a pretty crude design. I added bits to it to adapt in the new bush.
Here a pic of my bottom mount, combination of std mounting plates with a shortened GP4 Escort 4 link arm fitted between, nylon bush one end, rose joint the other . Worked quite well, bad pic but got fed up fighting with photobucket - life's too short!!
