13 replies to this topic

[mattmiglia]

Am doing some work on my single bolt front subframe and want to check its square and true. Any advice how to do it without a jig?

[Ethel]

Lots of measurements. If two points on the left are the same distance apart as the mirrored dimension on the right and the diagonals between the sides are the same length you have symmetry.

 

[Spider]

While the above drawing is helpful to a degree 99% of the time, the subframes get twisted, in which case, you'll likely find referencing the above drawings all will measure up OK as they don't pick up any twisting.

 

While seeming a little crude and short of putting them in a jig, I've found eyeing off across the subframe, one rail to the other can be quite telling and will show up a twist.

[mattmiglia]

Yes the measurements are helpful but as moke says it doesnt tell a twist so easily.

My suspicions are from having it sat on a 18mm thick piece of timber it rocks almost diagonally

[Spider]

The measurements are also only for a twin bolt, MKI and early MKII types, not the single bolt, rubber mounted frame (sorry Ethal).

 

This is what I was banging on about

 

[mattmiglia]

Ive clamped the toe board mounts to the solid board its sat on....one tie bar mount is still sat on the board while the other is now 20mm in the air

[Ethel]

Yes the measurements are helpful but as moke says it doesnt tell a twist so easily.

My suspicions are from having it sat on a 18mm thick piece of timber it rocks almost diagonally

As I said, measure diagonals they'll be the same if it's true (a square is a parallelogram with equal diagonals as well as sides). You could pick the 3 mounting points and construct a triangle on each side Front panel, tower top, toe board. Those dimensions should match comparing side to side. Then front panel left to tower top right should be the same as tower top left to to front panel right. Do all combinations and you'll have covered all three planes and should have a better idea of where it's twisted.

 

You could also extend the line of the top arm pins and bottom arm/ tie bar attachments with rods or taught string.

[Spider]

Ive clamped the toe board mounts to the solid board its sat on....one tie bar mount is still sat on the board while the other is now 20mm in the air

 

It does sound twisted. They are not spot on, but usually better than 3 mm.

[Ethel]

 

Ive clamped the toe board mounts to the solid board its sat on....one tie bar mount is still sat on the board while the other is now 20mm in the air

 

It does sound twisted. They are not spot on, but usually better than 3 mm.

 

Could just be battered under the bottom arm, a less sturdy area that gets used for jacking.

[Swift_General]

If you have a digital inclinometer or can borrow one you can place it across the rear mounts and the front cross price which should give you a very good idea of any twist.

[panky]

'Make the noise'

[mattmiglia]

Thanks everyone. I can confirm its scrap. Has been placed outside for the local bent subframe collector

[Homersimpson]

I know yoiu have already resolved this but could you not have used a spirt level to set the frame level at the front and then check the back and then do left and right?

[mattmiglia]

I didnt need to it was that bad, it was visibly way off once clamped level at the back