Cracked Power Plant Frame (PPF)

deviant · Postby **deviant** » Mon Jan 17, 2011 8:28 pm

Can any of you guys that have suffered a cracked PPF describe the symptoms for me?

I am hearing a loud metallic ping or tick from under the car when I take up drive in a more vigorous fashion....like if I go for a sharp get away or on fast gear changes (only 1st-2nd-3rd). It sounds a bit like a large stone or something hitting the underside of the car. It also does it if I do something like roll in 2nd gear and then bring in a large throttle input.

What is the go for fixing it? I assume that if it is just a crack it can be tigged up but is this likely to last? If it is anything like the one Hammer suffered that looks like it shattered I assume it is just scrap.

My car is turbocharged with over 200BHP at the treads and 300NM torque and is used on track more than road so is there anything I can do to stop it happening again....any opinions on this: http://www.good-win-racing.com/Mazda-Pe ... -1006.html

Hammer · Postby **Hammer** » Tue Jan 18, 2011 12:24 am

How you describe on what you're hearing is exactly how mine sounded. It drove me mad as I could not locate it until it was hoisted and the crack was visible.

That's the only way you can confirm if it is.

It also depends on the crack if you can get away by welding it. Keeping in mind the engine/diff will always try to twist it (rotating forces). It might be better (and safer) to source a 2nd hand version and replace it altogether.

Guran · Postby **Guran** » Tue Jan 18, 2011 7:59 am

It's worth noting that the PPF is made from a heat-treated (T6) aluminium alloy (A6061). I'd be a bit concerned about the weld and adjacent heat affected zone being a potential weak point. Make sure your welder REALLY knows what they're doing. If it were me, I'd be replacing it if it's cracked.

Garry · Postby **Garry** » Tue Jan 18, 2011 11:00 am

Some more crackage sources for HiPo MX5's is the rear subframe brace. David from Mania found the start of a crack in mine at the last service and said he'd come across a few cracked ones. One "mountain dríven" SE he mentioned was particularily bad.

Postby **Okibi** » Tue Jan 18, 2011 3:06 pm

Seems like it's best to go under and look, If the diff bolts were starting to work themselves loose could it make the same sound?

deviant · Postby **deviant** » Tue Jan 18, 2011 3:45 pm

Annoyingly it does not seem to be there today :evil:

but I also did not really have chance to open the taps to much.

Think I might run it to my mechanic and get it in the air and have a good poke around. Heck even if there is nothing going on I think there are enough stories around of the PPF failing that anyone with a hi-po or hard dríven MX5 should make an inspection a regular routine.

Benny · Postby **Benny** » Tue Jan 18, 2011 3:54 pm

I have suspicions about mine too.

Is there anything else you can do about it apart form repairing or replacing it?
Is there a stronger PPF made by anyone?

Postby **Boyracer** » Tue Jan 18, 2011 5:27 pm

I have few in the shed if anyone needs to replace theirs these have been nowhere near a SP or anything with big power.

Postby **Okibi** » Tue Jan 18, 2011 6:18 pm

deviant wrote:...I might run it to my mechanic and get it in the air and have a good poke around...

Which mechanic do you use? It's always handy to know which ones are familiar with the MX-5.

Postby **orx626** » Tue Jan 18, 2011 9:48 pm

Guran wrote:It's worth noting that the PPF is made from a heat-treated (T6) aluminium alloy (A6061). I'd be a bit concerned about the weld and adjacent heat affected zone being a potential weak point. Make sure your welder REALLY knows what they're doing. If it were me, I'd be replacing it if it's cracked.

Whole heartedly agree Guran!

I'd just replace it rather than weld it.

Cheers,
Danny

deviant · Postby **deviant** » Wed Jan 19, 2011 11:00 am

Benny wrote:I have suspicions about mine too.

Is there anything else you can do about it apart form repairing or replacing it?
Is there a stronger PPF made by anyone?

I have never found one. No doubt you could bolt braces all over the thing or weld some extra strength in to it (taking note of what it is made from) but at the end of the day it still only has a couple of fixing points that bolt to something that moves a fair bit under load. Also each end of the PPF is bolted to something that moves in a different direct to each other...the gearbox twists it and the diff bends it. Any strength you add along the PPF is going to increase the load on its mounting points.
I would guess that if you wanted to make something to replace it then it would have to be something like a FM butterfly brace / frame rail kit with a PPF built in to it than can provide more than a couple of mounting points for the gearbox and diff. Perhaps solid diff and gearbox mounts would help but for some people the noise and vibration would not be acceptable.

It is good to know that there are a number of used PPF's floating around though.

Okibi wrote:
deviant wrote:...I might run it to my mechanic and get it in the air and have a good poke around...

Which mechanic do you use? It's always handy to know which ones are familiar with the MX-5.

GTI Performance in Bibra Lake, they also tuned my car. I believe they have also worked on a couple of other club member cars. There is also a tarmac rally style NA that they work on....its bright green with a black hard top and a full cage. There is a glimpse of it in the club callendar.

I just remembered though that their mechanic has just left them to lecture at the MTA...bugger! He was a really really good mechanic, lots of motorsport experience and was a proper mechanic in the sense that he could fault find and could turn his hand to everything from a routine service to manufacturing bits and pieces.

Even without him there anymore I would still talk to GTI for stuff, Simon Gunson is the owner and he really knows his stuff so will probably try and help you out. He is a weapon driver to.

Having just said all of that......I just had a look at their website http://www.gti-pc.com.au/performance/index.html and the advert for a mechanic has gone and they are building another Targa spec Evo so it looks like they might have someone in. I know Simon had a very specific idea of who he would employ as a mechanic so I would trust whoever he has picked. I might swing by later and be nosey. I work a couple of blocks over from their workshop.

Techno · Postby **Techno** » Thu Jan 20, 2011 8:59 pm

I recently had mine TIG welded by a chap who specialises in car building (was fitting torque boxes to his 64 'stang when I arrived)

The issue is that it won't always be just one crack ... it is usual for aluminium of this type to crack/shatter (a bit like old windcreen glass) so that the one break you can see will often be surrounded with weakenings which need multiple welds.

Whilst I have every confidence in the welder and his work it would be more comforting to have a new one fitted.

If I were in the same situation I again (hope not) I would go for a replacement ... for pease of mind.

PS I think mine broke when there was a giant hicough while in second and coming off the throttle... but I didn't have an ongoing creaking or cracking sound.

Regards

Rob

deviant · Postby **deviant** » Fri Jan 21, 2011 12:09 am

If you look at the pics of the one hammer replaced the ally has shattered.

mitch_f1 · Postby **mitch_f1** » Fri Jan 21, 2011 10:08 pm

Does it sound right that one would be cracked in a fairly stock NA. Like I am getting a cracking sound now when I put any kind of torsion through the car. For instance, coming out of the driveway at an angle, or going through the second last corner at wakefield park??