Jimbo Sage

I have a question I would like to have opinions on. I have seen it here in the past that some of you think it okay to reuse metal gaskets around the exhaust and turbocharger. I am in the process of reinstalling my rebuilt stock twin turbocharger and I don't want to buy any more gaskets than actually necessary. I have gotten prices from Ray Malloy. The turbo back from the rebuilder looking nice, however it has some side play in the compressor shafts. With a new nebuilt should there be any play.
Thanks for your reply

dgeesaman

iTrader: (7)

A little side-side play is normal, although it should be a lot less than before the rebuild. It's the axial (in-out) play that should be absolutely zero. I'm curious who you had do the rebuild and what they though of it.

I think reusing the gaskets is a safe thing to do since you're reusing the same manifolds and the gaskets shape prevents assembling it in a different way. If it were a different manifold I would not.

However, the studs and nuts would also have to go back into the same exact holes or else they will not compress properly. You can either add a single flat washer under each one or just buy all new hardware. The new Mazda hardware ain't cheap, but it's really durable stuff. There are other places to buy exhaust studs and nuts (atpturbo.com) but I'm not convinced it's as strong or corrosion resistant as the Mazda hardware.

Dave

Jimbo Sage

Dave
I had B & D Fuel injection service inc. do the rebuild. They just told me that a lot of rebuilders will not work on the mazda turbo. I don't quite understand the bolt situation as you referred too. Could you further explain. This turbo was installed recently by a dealer and everything was fresh, we had no trouble getting the bolts loose. You don't think using the metal gaskets is a problem, what about the others, such as oil lines, coolant lines, etc.
thanks for the response
Jim

Montego

iTrader: (1)

rebuilt stock turbos... I have zero confidence in their reliability. With that said i hope that they last you a while before they start leaking.

RotaryResurrection

iTrader: (8)

Reuse the gaskets. It isn't a rocketship we're building here. As long as the gaskets are not creased or rotted through anywhere they will seal just fine. The 87-88 turbo gaskets are the only ones I ever see that are actually bad.

Also I have never heard of anything except heads and rods on a piston engine where you needed to keep the hardware in the same identical position. This is not that big a deal guys, just bolt it down securely and go.

Jimbo Sage

Me Too.

dgeesaman

iTrader: (7)

These aren't bolts. They are assemblies that have frozen together, exactly recording the thickness of the flange they had bolted down.

Used turbo studs and nuts tend to gall together very quickly to form a 'bolt'. At the original installation, the stud bottoms out in the tapped hole, then the nut tightens down on the manifold flange. Then heat cycle a few hundred times and let the bolt and nut gall into one inseparable part.

Now remove that bolt, and when you install it again it will thread into the new hole and stop when either the nut bottoms against the flange, or the stud threads bottom into the tapped hole. In the second case, if the nut is galled it the nut won't turn anymore, and that means the nut is not in tight contact with the manifold flange. Even if the nut does turn on the stud, the elevated friction will mean most of the torque is not put into preloading the stud.

Since every stud location on the manifold has a different thickness of flange, if you mix up the frozen stud/nut parts then on average half of them will not apply any clamping force. How often, and how severe this effect is, I can't exactly say. But I have noticed that even low mileage studs and nuts will not clamp a downpipe or turbo flange firmly.

The solution when reusing frozen studs and nuts IMHO is to use a flat washer under each nut. The credit for this idea goes to BigIslandSevens, IIRC. This extra thickness will prevent the stud threads from bottoming out in the flange and ensure that the torque you apply goes into clamping the joint. I have not tried it, but a thin stainless SAE washer under each is very simple insurance to get good even clamping on the flanges.

Dave

Jimbo Sage

Dave
Thanks for the explanation, I understand it now.
Jim

RotaryResurrection

iTrader: (8)

The problem with putting washers underneath is that you reduce the amount of threading into the manifold, increasing the chances that the stud strips when you put torque on it. It's unlikely in the cast iron manifold, but still a consideration.

I've never had a problem getting the nut/stud combo to tighten firmly onto hardware even when mixed up. The stud goes in until it bottoms out and the nut turns maybe an extra 1/4 turn until it is tight. Each to their own, I guess. I just dislike it when "armchair engineers" start posting stuff that is entirely possible in theory but not usually applicable in practice, in an attempt to scare unknowing posters such as this guy into buying a bunch of unnecessary parts "just because you want to do the job right".

dgeesaman

iTrader: (7)

That's why I suggested SAE washers and not a split lock washer or something thicker. An SAE washer will use up less than one turn of M10 thread. Frankly, if the alternative is improper clamping, I'll happily give up the fraction of engaged threads in this case.

If I were being unnecessarily thorough, I guess I could leave my .0005" feeler under the gasket and see if it slides out when my torque wrench first clicks. Then I'd know if I have to put a washer under that one.

I wish I had the same experience. When I've done it, either the nut won't turn any further or the amount of torque to make the nut turn is substantially higher. The experience you describe is how I hope it turns out for everyone else.

Well like I said I have not had the same experience as you with these seized manifold fasteners, and the cost of a dozen M10 stainless washers is a ridiculous argument. I assume you were more referring to the idea of buying all new hardware.

While I don't turn nuts on RX-7 manifolds every day, I do work with rebuilding machines on a regular basis. I'm not making this stuff up. (not today at least ) Doing rotary work would be way cooler.

Dave

danny hahn

I'm the one that recommended B & D as I have 10,000 miles on mine.

I was surprised that you have side to side play. Though it was alittle over 2 years ago, I felt my tolerances were pretty tight. I'll have a conversation with the mechanic who installed it about his recollection. Before install I'd give Gibby a call if you haven't already. How was the returned product and how much?

Gaskets I think I ended up replacing one, were those about a half dozen sandwiched copper? I think I had one with a piece missing, so it was obvious. No I'll effects from reusing gasket.

The Nuts, by design the locking mechanism is soft steel on the back, they are reusable by resquishing the back end in a vise. I think I ended up replacing 1 or 2 of them and I probably got them from Malloy because I was placing an order for some parts. But I think you can get some from mcmaster.com

dgeesaman

iTrader: (7)

This has been debated some but the Mazda studs and nuts are not a common material - my guess is that it's a 400 series stainless or other high alloy. They are slightly magnetic, and ungodly expensive. Considering how these look after a few years in service I think a lesser material could end up failing. I also searched for nuts shaped like that and was unable to find anything in any material. You won't find a self-locking and compact head like that at any common fastener shop.

Dave

vtakk eg

^ i think rotary ressurection does a little machine rebuilding too, dave
what are those machines called he works on?....oh yeah thats right 13B's
im am lucky to have a rotary specialist only 45 min. down the road

danny hahn

were the nuts like $9 a piece?

Mahjik

iTrader: (1)

The Mazda nuts are inconel (as noted in the following thread):

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/twin-turbo-nuts-bolts-586150/

Jimbo Sage

Danny
Yea I got the information from you on the B & D service inc. I did call them and they seem to agree that some side play was permissable. My thoughts were after fitting new bearings and seals that there would be no play. Still not convinced. This turbo was installed by a dealer when they installed a remanufactured engine, so the fasteners were easily removed. The cost of the rebuild was $1025.
Thanks to all you guys for the information, it helps to work on others experience.
Jim

alexdimen

iTrader: (13)

The reason that there is always some play is that these are float bearings IIRC, so side to side play is normal. Float bearings are suspended between the housing and turbine shaft by a layer of oil.

Jimbo Sage

Thanks alexdimen your comments answer my question of side play on my newly rebuilt turbo.
Jim

danny hahn

Hey I was reading some of your other post. Did I read right where you've owned the other gens, this is your second engine, 2nd round on turbo's, blame pump gas for blowing 1st after how many miles? What are you doing to avoid this? Injectors in good shape?

MontegoRx

Gotta chime in on this one, I suppose. Keep in mind I'm not an "armchair engineer".

While Dave might've slipped a bit with claiming that the washer retains the clamping force, I do believe that the washer method is a nice insurance policy. The issue with clamping force would be the amount of teeth holding inside the manifold. In any case, the first two teeth (only two) hold an ungodly amount of the tension (not torque). Since bolts fail in tension only, I'd be inclined to say that a lock washer would be even better than flat (perhaps belville if you're frisky). This would keep the torque applied to the join and resist any kind of 'negative torque' that might back it out before it heat cycles into place (as Dave noted, and it's true, it happens quite often).

My solution, since I figured I'd be a test mule and had access to free parts, was to get bolts matching the pitch and mix up the length. I cleaned out all of the holes, ran the bolts through the manifold (with no DP in place) to gauge by eye how far they would go until they bottomed out. I went with the size that fit slightly tighter than the thickness of the DP flange. This way, I didn't have to worry about the washers (remember the ungodly forces on the first two teeth), and I had bolts instead of a two-part stud/nut system that would give me hell later.

Right now, I'm not totally convinced that I'm getting a great seal, even with a brand new gasket; however, I have a used DP on the car which might have been slightly warped. If it's leaking, it's not enough to damage any performance of the car, but i have a feeling that there is a slight leak. Once the weather warms up a bit, I plan on pulling the joint apart and checking the gasket for any signs of leakage. If there's leakage, then I can at least find out where and why it was leaking. If there's no leaks, then the bolt method seems to be the way I'd recommend. I forget the exact dimensions, but I know it was a 16mm head (making tightening a LONG process at 1/16 turn per shot on some) and I forget the pitch and length. I can try to get the stats if I have it apart, though.

dgeesaman

iTrader: (7)

I don't think I communicated the problem I had clearly.

The stud has an unthreaded section. When you thread it into the ex manifold, that unthreaded portion reaches the start of the manifold threads and stops it from turning further.

The nut turns on the stud, and stops turning when it's squeezing on the turbo manifold flange. The torque you apply now simultaneously seats both the stud into the ex manifold and the nut onto the stud.

If you remove these many miles later, that nut seizes (galls) on the stud, then the nut is positioned on the stud such that when you tighten into another hole location, one of two things will happen:

1) this location has a thicker turbo manifold flange, and the stud/nut stops when the nut clamps on the manifold. The stud threading never bottoms out in the exhaust manifold. This is fine, since the turbo manifold is being clamped down by the torque.

2) the turbo manifold flange at the new location is thinner than before, and the stud bottoms out in the ex manifold threads before the nut is clamping the turbo manifold flange. 2a) (the situation RR described) the nut then turns some more on the stud, and the turbo manifold flange gets clamped. 2b) (my bad result) the nut is really seized, and will not turn further. The torque wrench clicks, it looks properly assembled, and you go on never realizing the manifold flange and gasket have no compression.

My use of the plain (flat) washer is to take up the little bit of length to avoid 2b. Or use a very thin feeler gauge to feel that the flange is actually being clamped.

Dave

MontegoRx

Dave, I read one sentence and quit at that point.

You're correct about the unthreaded section. Placing a washer would definately stop that section from hitting, and would give you the thread depth minus washer thickness (washer thickness being nearly useless). I was writing my post and forgot about the little "bubble" in the middle of the stock studs.

I never disbelieved in the washer theory, and I figured I'd try some other ones out, but I'll be damned if I watch someone come in here calling Dave an "archair engineer" without at least throwing my .02 in.

By the way, how many people had to google "belleville washer".... c'mon dave... ya know you did

MontegoRx

btw, just noticed I mispelled belleville washer in my first post because my best man (and I was his) has a last name of belville.

dgeesaman

iTrader: (7)

If I spent half the time actually doing on rx7s that I spend thinking about them...I wouldn't sound like an armchair engineer.

Actually I caught that but didn't need to check.

Dave

Joe Geiman

Regarding washers under stud/nut "bolts':

1. I thought that a screw thread could be torqued to maximum torque spec at 1:1 depth to diameter. You should not have to have thread engagement to 2X depth or anything like that.

2. The nuts are copper so maybe you would want to use copper washers under them to keep the same coefficent of expansion. Also, copper will get harder each time it heat cycles. Maybe that contibutes to it's ability for the nuts to freeze to the stud.

3. Also, you can anneal the copper nuts by heating them with a torch and they will become soft again, thereby aiding in removal.