Can you ever know if a frame is straight?

"D" (danjee)
11/09/2014 at 19:35 • Filed to: None

My friend has a Miata with healthy guts but a bent frame. So, he's looking for another Miata with a straight frame, and then he can swap over any necessary mechanical bits from his old car. He's operating out of a slim budget, so we're scraping the bottom of the Craigslist barrel for Miata carcasses. Found one—it would be the perfect candidate if the frame was straight, but it's been in a minor accident so we can't know whether it is or not.

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It's not in the ad, but the owner says he hit the front corner of the car once. My friend checked out this car and looked carefully for signs of frame damage (misaligned body panels, etc) and didn't see any red flags, although he's still apprehensive because he can't know for sure.

Are there any ways of coming to actual conclusions about the state of the frame? All I can think of is if a) no unusual panel gaps and b) the car drives straight with a fresh alignment... but this obviously couldn't be tested on cars such as the one in the ad.

DISCUSSION (27)

Sportwägen, Driver Of The Red Sportwagen > D
11/09/2014 at 19:37

Buy it, if it doesn't work out, scrap it but save the interior and engine/trans...

dem seats tho ;)

D > Sportwägen, Driver Of The Red Sportwagen
11/09/2014 at 19:41

It's not my money, it's my friend's, and he really wants something he can work with, not another NA to sit idly on his property

Sportwägen, Driver Of The Red Sportwagen > D
11/09/2014 at 19:42

If the frame is straight, use the frame and sell the other unwanted parts for profit

If the frame is no good, strip it and sell the usable parts and scrap the rest

Simple!

 > D
11/09/2014 at 19:43

Seeing how Miata is unibody there is no frame. The only true way to know if a frame or unibody is straight is to put it on a rack.

claramag, Mustaco Master > D
11/09/2014 at 19:44

I usually buy frame bent cars for the savings, so my eyes are a little trained for it. Appreciate the poster showing the damage, that looks pretty damn bent to me in the last pic. Might not have affected suspension mounting, but if your friend is seeking a perfect frame this doesn't look like a winner

Old-Busted-Hotness > D
11/09/2014 at 19:54

A factory shop manual will have all the measurements. Side to side, corner to corner, and where to measure from. It's a hell of a lot easier if you have access to a lift.

D > Sportwägen, Driver Of The Red Sportwagen
11/09/2014 at 19:54

Your logic sucks. If he could know just by looking at it, then he could go check it out again, buy it, and use it for his project. But since he can't know just by looking, he'd have to build up the entire car first and wait and see if the frame turns out bad, such as it doesn't drive down the road straight or whoops, I can't mount this shock. My friend works and go to school, he's certainly not going to take the "wait and see" approach to detecting frame damage. He's willing to put in the effort to build up a car, but only if a drivable car is the result—not for small profits or loss-cutting.

Tinfoil Hat in a thunderstorm, now with added diecast > D
11/09/2014 at 19:55

You could try a tape measure between points that should be symmetrical, like top corner of the windscreen posts to the front corners of the boot(trunk?) take measurements between these points both from the same sides but most importantly take diagonal dimensions as accurately as possible, any twist will show up if the dimensions are not close to the same. Accuracy is important and recheck more than once. Also have a known straight car to compare the results. Hint; use tape on the places you measure from so you can use a pencil or marker to make reference points. Good luck

D >
11/09/2014 at 19:56

It's actually a unibody with front and rear subframes but yeah, by frame I mean "this assembly." And yeah, sounds like he'd have to buy it in order to be sure :(

D > Tinfoil Hat in a thunderstorm, now with added diecast
11/09/2014 at 19:56

This is good advice, I'll pass it along

D > Old-Busted-Hotness
11/09/2014 at 19:58

noted! I'll let him know

D > claramag, Mustaco Master
11/09/2014 at 20:00

Good wisdom. I'd reckon he's seeking an "effectively perfect" frame, i.e. a frame that does not pose any problems over a truly perfect one.

Soloburrito > D
11/09/2014 at 20:00

Tell your friend keep the miata rollerskate and save up for an exocet miata. Or sell the rollerskate to someone who wants to build an exocet and buy a whole miata.

Sportwägen, Driver Of The Red Sportwagen > D
11/09/2014 at 20:03

What I'm saying is that if it were me, I would buy it (offer $500), strip the panels, and find a way to get it on an alignment machine, and see if it was straight.

If not, scrap the chassis and frame and sell the interior and drive train.

That's just how I would do it.

D > Sportwägen, Driver Of The Red Sportwagen
11/09/2014 at 20:04

That's certainly a plan, just an extremely effort-intensive plan.

Tinfoil Hat in a thunderstorm, now with added diecast > D
11/09/2014 at 20:05

No worries, hope it works out. Those seats look like they would be worth the asking price, down in Australia at least.

D > Soloburrito
11/09/2014 at 20:05

Yeah. There's the a whole world of other options... but that's a different topic for a different day.

Sportwägen, Driver Of The Red Sportwagen > D
11/09/2014 at 20:08

Yeah it would be. But the reward is potentially greater than the risk in this case!

Me:

Kinja'd!!!

You:

Kinja'd!!!

D > Sportwägen, Driver Of The Red Sportwagen
11/09/2014 at 20:12

No, you don't get life. The effort—money, time, and exertion—to pull off your idea is simply unavailable to my friend.

claramag, Mustaco Master > D
11/09/2014 at 20:12

Ehh, what's a few 1/10th degrees of caster between friends right? The outer edges under the bay where the hood rests are sometimes a good place to check for front frame (sorry, unibody ) damage.

Although if he's that tight on funds, maybe a new frame is just out of the question. Is the old oneso severe that it's just not prudent to keep it?

Sportwägen, Driver Of The Red Sportwagen > D
11/09/2014 at 20:15

That might be because I don't have a job... yeah that's it.

Tell him to try to find a Miata with just a blown motor or a bare chassis for cheap.

D > claramag, Mustaco Master
11/09/2014 at 20:17

Yeah old one is an an angle from the windshield forward. Door and fender panels are touching on one side, wide open on the other

claramag, Mustaco Master > D
11/09/2014 at 20:21

Ooh, damn. Yeah sounds more like an old fox body than a trackable miata. Well this just doesn't look like a winner, but open eyes'll find one in due time. Shame, those're some nice seats

D > claramag, Mustaco Master
11/09/2014 at 20:23

Yeah, the hunt continues. And those certainly are nice seats, especially considering the rest of the car..

bhardoin > D
11/09/2014 at 21:17

When I was working in a tire shop, we'd often get cars on the alignment rack that we suspected had bent parts because of either off-spec caster or unfixable toe. We'd usually end up using a piece of string and making sure that bits that should be symetric are actually symetric. This would probably be really tough to do without a rack.

The Stig's Rustbelt Cousin > D
11/10/2014 at 18:37

Check the frame rails (or unibody rails, as the case may be) for bends or wrinkles. Fresh undercoating is also a good sign that the car has previously-repaired frame damage. Also, check under the hood for signs of damage to the unirails (the engine is mounted to these) for similar damage.

Another good way to tell is by putting the car on an alignment rack, and seeing if the alignment is within spec, or barely so. On some vehicles, the non-adjustable measurements (ie caster) can tell you if the frame is as straight as is should be.

Captain of the Enterprise > D
11/11/2014 at 16:56

I would use the junk yard approach in reverse, typically you pull an engine out of a car that's been in an accident because the engine went wrong. So buy a miata with an engine that went wrong and a good body.