Topic

There are no planned MGF runs for a while and I have other cars on the road, so decided to complete the subframe mounting replacement and addition of a X brace. I have been soaking in penetrating oil for a few weeks and gave it another 24 hour douse this weekend then dropped out the front subframe rear mounting bolts.

Bolts came out easy enough However, they have been on a diet.... I assume the abrasion on the subframe has taken off the zinc coating and then the threads have gone (crushed and rotted)now looks like the tin weevil were in the home straight for eating through the rest of the fixing. I'm glad I did the job because another year and these could have snapped in leaving a whole different type of problem. Might be one to add to the maintenance list for checking/changing these fixings before they fail or corrode to the point of drilling them out.

TB

Are you replacing them with OE spec or is this a good application for stainless steel? Interesting post - thanks.

Richard

Apparently stainless steel doesn't have the sheer strength needed for these sub frame bolts so it's o.e. all the way.

Invalid or non-existent item ID.Invalid or non-existent item ID.I got some zinc coated screws from Ebay

they should last another few years

TB

I would be leery about replacing the bolts with OE. I replaced a number of bolts/nuts under my MGF with OE parts and was shocked at their condition a year later. They looked like they had been there for many years. The quality of finish and the metal itself really s poor. I never used to see this kind of deterioration on older cars. (MGA/MGA, Triumph from the 50's-70's) If you replace with OE it would be a good idea to protect them with a spray of Waxoyl or similar. It may wash off but any little bit of protection will help

Interesting info from that bolt supplier:-

The MGF & MGTF subframes are bolted upwards into the floorpan & into enclosed box sections using thread-cutting bolts, great for ease & cost of factory assembly but not so great for the owner as the car gets older - they are very prone to rust, worsened by the fact they're thread-cutting type - the helix cut-out in the threads allows moisture to seep down the entire length of the thread, the resulting rust makes them progressively harder to remove and will eventually lead to them failing. Replace these with much stronger items (12.9 grade) with more durable anti-corrosion protection before the factory bolts degrade too badly and you'll avoid a potentially very large headache in the future. Bolts are supplied with stainless washers, set of 12 bolts does one subframe - 8 for rear mounts (replacing KYP10004), 4 for front mounts (replacing YYG10005A)

As an example, this significantly weakened bolt came out of a 2005 MGTF -

How big a job is it to replace these sub frame bolts

The job can be "easy"! However I was very lucky the bolts came out with no problems. I did it in 2 jobs, first the front mounts, changing the mount, fixings and through bolts. Then moved to the more dodgy rear mounts. Having read some horror stories of snapped bolts etc. I soaked both set of bolts for about 2 weeks before each attempt. In summary the fronts are easier to do because you can get to the threads, I think the rears are a lottery if they come out (silent prayers in order when you load up the breaker bar).

I allowed a full week off the road for each set, but only needed 2 hours on the fronts (including removing/replacing the bumper) and 30 mins for the rears, I had all the bolts ready and was prepared to do the drill out and Helicoil if needed (see CJJ how to). However, I had been jacking up the car and blasting the mounts for 2 weeks with penetrating fluid.

Learnings:

• Have a jack handy and set up to lift the car body as the axle stands will be under the subframe, this allows you to insert the big through bolt easily by moving the car up and down to line up the holes.
• Have a big breaker bar for the through bolts, its really tight I bent my trolley jack handle, slid over a small bar.
• Replace front mounts with Solid mounts on F, I used uprated ones from MGFandTFbitz.
• For through bolts see Diesel Destroyer who has some 50 odd special 12.9 Zinc coated beasts that I am sure he will be pleased to sell.

TB

Tourbillon wrote: wrote:

hack slash

Learnings:
snip snip

Replace front mounts with Solid mounts on F, I used uprated ones from MGFandTFbitz.

snip

TB

I am in the process of changing my front sub frame ATM but I was going to re fit the rubber mounts
Any reason you swapped yours?

Try one of the following options for solid sub-frame mounts:

£34 each delivered from MGFnTFbitz
MGF MG TF METRO FRONT SMALL SUBFRAME MOUNTING - SHOT BLASTED AND POWDER COATED Completed