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Discussion Starter · #1 ·
Any thoughts is this a known issue others have had? I re-used the 3 nuts on the manifold studs that connect it to the downpipe. Got new crushable fiber/metal sandwich gasket, but it keeps loosening up every 50 miles or so. I think I'll go get some lock washers? What say ye?
 

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Make sure whatever lock washers you get are capable of staying a lock washer at 1400*F+. Cheap ones from hardware stores tend to relax and just flatten out at most exhaust-manifold temps.

What are you torqueing them to? I'd try +5 ft-lbs each time they loosen up and see if you find a sweet spot where they stay put.
 

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Look into Nord-Lock washers.
 

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Discussion Starter · #4 ·
I couldn't find a torque setting for them, actually. So, I've been tightening them up slightly each of the 3 times. Good reminder on the temp. Perhaps someone makes a heavy bolt with a locking feature that I can find. I'll have to get the thread count and look online. Anyone know the size/pitch?
 

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To hold exhaust system parts together, I usually start around 45ft-lbs and go up to 60ish if needed, but past 60 I start looking at what isn't aligned properly and/or rattling to shake it all loose. That doesn't usually happen on a Supra unless there's a shitload of heavy exhaust piping and no flex sections.

The stock hardware is M10x1.25 IIRC, might be M10x1.5. Been awhile since I've seen an 7M-GE exhaust manifold but M10x1.25 is what almost all M10 stuff is in a Toyota of this vintage.

The only exception the 7M exhaust manifold flange itself, which I tediously set up with cleaned studs with high temp loc-tite (helicoils if needed) and I start with 20 ft-lbs to get things set, then I do two more +10 passes to end up at 40 ft lbs. Then I heat cycle it at least 2-3 times to settle the gasket and such, and do one more pass through to 45ft-lbs.
 
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Discussion Starter · #6 ·
Thanks, good procedure. I'm also wondering why it keeps loosening. The engine's running smoothly, this is the original exhaust which is in near perfect shape, I wire brushed the 3 studs to perfection, lapped the manifold's mounting face flat and clean, and the smooth engine's sitting on new motor mounts. So I think I did my part!!

I picked up some M10X1.25 steel locking nuts from Fastenal. They have a trichoid shape at the top that adds 10.5lbs-ft when the top of the nut arrives at the stud threads for the locking effect. I also picked up some high carbon locking nuts and may use both just because I don't want to deal with this again. Winter's around the corner and laying under the car tightening exhaust bolts will go from "hmm, that's a pain" to "really - that's it till spring, I've HAD it" really fast.

I think these original locking nuts are just not locking well and I've been a bit cowardly on the torque without knowing the correct torque for the 3 bolts. I've got the front end on jackstands for the latest tightening, so I'll swap them out after dinner and see how long that lasts. I might release all 3 and let it down slightly so I can see with a mirror that the two gasket like deals are in the right spot still. Or I might not want the thing to pop loose and then deal with getting them aligned and back up on the studs...

If anyone finds a torque setting, let me know. I will look in the FSM for the usual Toyota torque chart by fastener size they use as a generic guide.
 

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Discussion Starter · #8 ·
Perfect! So, I used both the steel locking nut and the lock washer and cranked it to 45 ft-lbs. Just walked back in from the garage. That was definitely more than I'd used previously so we may be done with that nagging little repeat issue. Thanks!
 

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do you have a new o2 sensor in there ? maybe its running hot as hell / lean / has a slow sensor. these are like gen 1 narrow band, heated sensors. have you pulled the plugs to see whats going on ? I would strongly recommend that if you didn't have the injectors cleaned and flow tested. you put a lot of work in, id read the plugs and evaluate (exh loosing that quick is weird and maybe suggests excessive heat)

could also be that rebuilt 7m just rejecting that NA manifold, because it wants boost. don't get me wrong, the car is mechanically just great man, Ive enjoyed all this rebuild madness.....but its like 7PSI away from just next level bad ass haha
 

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Discussion Starter · #10 ·
Heh, no I think its from me reusing the factory locking nuts. They seem to have lost their tension. I cleaned the injectors n it is running well. In fact now I'm wondering what effect my port matching and head work had on HP and wondering if there's a dyno around! It feels good at low rpms, and very good at higher revs now that the breakin oil is out.
 

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Use the proper nuts

Body jewelry Font Jewellery Fashion accessory Circle


NCF10X1.25X14 - Copper Flange Nut Fine Thread Wide Flange [NCF10X1.25X14] - $1.53 : Bel-Metric, Metric Hardware, Metric Fasteners, Metric Bolts, Metric Nuts & Time-Sert Thread Repair
 

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Discussion Starter · #12 ·
Yeah, I have these on my Vanagon, but I was afraid the softer copper wouldn't provide enough torque for this location. Seems to be holding up now, but time will tell if it loosens, and also if the hot gases carved out the new gaskets I put in there. It doesn't take long sometimes. Hope not...
 

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Copper plated steel, read the description;)

The copper plating is for anti-seize properties
 

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Discussion Starter · #14 ·
Oh, got it. Plated. What I used looked like stainless steel and the lock washer was high carbon steel, so they'll likely come off well some day. I normally use copper based anti-sieze on all exhaust connections, but wiped it off here after the 2nd loosening episode. As an aside, the factory nuts came off the LandCruiser at 298k miles just fine - original exhaust never off. These also came off the Supra just fine and the car is completely original. At the end of the day, knowing that, the smartest thing would have been to get 3 more of those exact nuts from Toyota as clearly that design is a very solid one.....
 

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Ahh, hardware, a mistress I know all too well in some areas. Alan makes a great point about using the right type of nut. Also worth considering, is looking at the parts diagram for that area of the car. Quite possible that the nuts in question are not to be reused. Some types of locking hardware are a one time use only, unfortunately.

The suggestion of a Nord-lock washer is also a good one, as far as lock washers go, they are easily among the best. Expensive, but worth it.

I gather that you're talking about the hardware that holds the exhaust pipes together. If we're talking about the stuff that attaches the manifold to the head, or the turbo to the manifold, PLEASE use an appropriate material fastener. I can show you pictures of what it looks like when the shop that built your engine uses grade 5 hardware store bolts to assemble your engine... turns out metal fatigue is a VERY real thing, and the results are rage inducing. Stainless steel here, folks, quality at that. ARP is your friend here.

Another option that seems to work well is Stage 8 locking hardware.
 

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Discussion Starter · #16 ·
Wups, I was not clear what I did. I went to Fastenal and got 3 stainless nuts that have a 3-way pressed top that digs into the threads. So the top is distorted with a press into a Mazda rotor looking shape. Seemed very high quality. I also picked up hardened lock washers and when I put them on I torqued higher than I had been using. I will be under the car to install a fuel tank seal in a week or so and will look to see if it's holding fast. Thank you for the input.
 
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