Exhaust Gaskets partialy blocking ports?

[nkemp]

Fixing the exhaust ticking (caused by broken farthest forward passenger side stud...later found driver's side equivalent was broken as well) exposed a potential power robber. Take a look at the photos. You'll clearly see where the exhaust was blowing by on the failed bolt.

Notice also that some of the ports also show some exhaust blackening on the block and also on the manifold. This indicates that the gaskets were not centered on the exhaust ports (the gasket hole is offset from the port hole). It looks as if they may even had partially blocked the exhaust path in a couple cases. I checked the manifolds and the block against the new one piece exhaust gasket and the manifold ports are perfectly aligned with the block ports as would be expected.

I cannot say for sure, but as I looked at them, they sure looked like the gaskets partially blocked the ports. So I'm expecting about a 50hp boost after fixing:nana1:
44070440714407244073

May have been installed at the factory wrong. May have moved. Either way, a bit of restriction will be fixed soon ... I hope...broken bolt extraction gods willing!

[DMCMW Dave]

Either at the factory (doubtful) or by the DPO. I've seen that.

Most important part of this job is to resurface the cast iron manifolds. A belt sander is adequate but a machine shop will do a much better job. If there were pre-broken studs that's a pretty good indication that they are warped. If you just toss them back on the car, you'll be doing the job over again in a short period of time.

[davidc89]

You probably won't know how to handle all that new found power!

[sdg3205]

Good luck keeping your tires planted with those extra ponies.

[davidc89]

44089

[nkemp]

Most important part of this job is to resurface the cast iron manifolds.

I had them machined at the local engine rebuilder. And I had him remove the bolts rather than me messing with them. Best money I spent lately!

If the front manifold studs are prone to breaking, it begs the question about upsizing or stronger studs.

[David T]

I had them machined at the local engine rebuilder. And I had him remove the bolts rather than me messing with them. Best money I spent lately!

If the front manifold studs are prone to breaking, it begs the question about upsizing or stronger studs.

I find it hard to believe it was a factory problem, we just haven't seen it across the fleet. Take the old gaskets and just lay them over the manifold and see how they match up. Then do it on the cylinder head. As for the bolts, once the gasket blows out it over-stresses the studs and then they break and the manifold warps. If the gaskets were blocking the ports it was, more than likely, done by a DPO or his mechanic using the wrong gaskets. As for replacing the studs, PJ Grady sells S/S ones that won't rot. Use Never-Seize when you put it back together. Make sure the holes in the manifold are large enough so that the manifold can expand and contract without breaking the bolts. It MUST be able to expand and contract a little and the holes may need to be enlarged. When the gasket blows out the manifold expands a lot more at that point and that is when the bolts break, it shears them right off.

[DMCMW Dave]

I had them machined at the local engine rebuilder. And I had him remove the bolts rather than me messing with them. Best money I spent lately!

If the front manifold studs are prone to breaking, it begs the question about upsizing or stronger studs.

Yeah - there are just some jobs that are not worth doing yourself.

I've never upsized the studs, but I've seen a few cars with bigger bolts used on a hole or two. I hate those as bolts screwed into the aluminum are almost guaranteed to be trouble at a later date. I've noted that similar designs on other contemporary cars (BMW) use 8MM studs. As David T noted, if you do that, make the holes in the manifold bigger too. Not as simple as it sounds because the washer recesses in the manifolds will be to small for 8MM washers to seat properly. And so on.

BTW if you do change the size, do them all and keep them metric! It really drives me nuts when you find a car with different sized fasteners holding one part in place, especially when they mix metric and fractional!

[content22207_2]

If the front manifold studs are prone to breaking, it begs the question about upsizing or stronger studs.

OEM 1mm thread pitch is virtually identical to 24 TPI. A 5/16-24 tap will follow the original holes effortlessly. When (if) I get around to replacing #2508's exhaust manifold gaskets, I intend to upgrade to Grade 8 5/16-24 studs. I will likely get double cut studs (5/16-18 threads on the nut end) to make future manifold removal easier. Holes in the manifolds and gaskets are 8mm (5/16") diameter already.

I've had an apple from this barrel before: My old Renault block used 5/16-24 intake manifold hold down bolts (I tapped them myself because the original bolt hole threads were frigged).

Bill Robertson
#5939

[nkemp]

It is possible that as the gaskets fail/age/weaken that the exhaust pressure moves them towards the the least resistance. That could explain the the hole moving and the gasket coming across the hole a bit.

[content22207_2]

I will likely get double cut studs (5/16-18 threads on the nut end) to make future manifold removal easier.

McMaster 94358A250 through 94358A280 should work nicely (whichever is closest to OEM length).

For comparison: Grade 8.8 is 115,000 lbs tensile strength (assuming OEM studs are even 8.8 ).

Bill Robertson
#5939

[DMC5180]

Nick,

Be sure to clean head surface before installing the new studs.

How did the shop remove the 2 broken forward studs?


Dennis

[nkemp]

The shop was not involved with removing the broken studs. The shop removed the 2 studs on the end of each manifold that connects to the crossover pipe.

I've been trying to get the studs out and I'm making no progress. I tried welding a nut to the stud but this is not a good application to learn how to weld. I fixed a kids rake, fixed the ice chisel and then tried welding the nut to the stud. It is so far forward and the car is not high enough to get close to it. I welded everything but the stud. No damage, just missing the target. Today I tried drilling the stud using a .62 inch thick guide. No lock on the first pass. I need to make another guide after enlarging the hole. Again access is the beast here.

What type of drill do you all use to drill the stud. I broke the LH HSS drill sold for this type job very quickly and without much pressure. And it didn't even leave a mark on the stud.

At this point, pulling the engine seems easier than getting the studs out while the engine is in the car!!!!

[DMC5180]

The drill was just a standard drill material nothing exotic. Where did the break occur? Down in the pilot hole or above the surface of the jig?


Dennis

[nkemp]

It broke after using it a bit. It was against the stud. It may have caught the uneven edge of the stud but since it had been used a little I doubt that. Maybe it was just prone to failure.

[DMC5180]

You do need to ease into it, but the bit needs to be spinning at a fairly fast rpm initially so the bit point can overcome any irregularity in the stud surface without snagging.


Dennis

[David T]

Probably easier to remove the head then to take the motor out. A right angle drill is what you want but if you have already made a mess of it you probably will have to remove the motor or the head to fix it. If you do take the head off it is much easier to take that to the machine shop and let them try to do it.

[nkemp]

Probably easier to remove the head then to take the motor out.

The exhaust studs are not in the heads. They are in the block. So removing the engine is likely easier than removing the block from the engine while in the car.

Currently no damage to the block (or stud). I have been moving slow and carefully so that I don't damage anything beyond repair.

For those who are heading into this repair, to drill you need an angle drill with a short head. About 2.5". Even then I needed to remove the rubber plug in the frame to get the clearance needed. The 1/8" bit is pretty tight (using a .62" thick guide). The next size down fits better but is pretty small. Many of the electric angle drives are about 4" and those will not fit.

[MikeWard]

For info replacement stainless manifold studs as well as crossover pipe studs are available from DCUK.

http://www.deloreanclub.uk/stainless-exhaust-manifold-stud.html

http://www.deloreanclub.uk/m10-stainless-exhaust-crossover-pipe-stud.html


And a good topic here ref removing snapped studs - engine removal not required: http://www.deloreaneurotec.uk/viewtopic.php?f=13&t=2383

[David T]

Check again. The exhaust manifold does in fact bolt directly to the head and not the block.

[DMC5180]

I guess I should patented that concept when I made mine 22 years ago [emoji6]http://uploads.tapatalk-cdn.com/20160630/c13ae86e2ee1ad297c61c9d47578a3b5.jpg
http://uploads.tapatalk-cdn.com/20160630/ee893c51d0a03fc48cb5c216de1cb696.jpg


Dennis

[nkemp]

Check again. The exhaust manifold does in fact bolt directly to the head and not the block.

I stand corrected.

[DMCMW Dave]

This may seem rather obvious, but you can cut the drill bit shorter.

This is very do-able. If we had to take the head off every time we deal with a broken stud, we'd be in a lot of trouble!

[DMC5180]

This is what I used 22 years ago. I bought the 90 drill just for the job.

1/8 drill bit initial pilot hole ( not shown )

5/32 LH (optional) drill for extractor

# 2 extractor

# 3 extractor (backup)

And my homemade drill jig posted previously

http://uploads.tapatalk-cdn.com/20160630/dd1875e49bdfea52736ac76a55bb108e.jpg





Dennis

[nkemp]

This may seem rather obvious, but you can cut the drill bit shorter. Dave, there you go again ... making things easier. I almost cut it shorter but it is shorter now:smile:

I blocked the car up a bit more and that has increased access. Increased access makes it an easier access which should help. Working at arms length just wasn't cutting it. A lift sure would be nice! Maybe I should put one on my gifster.com list.

[nkemp]

This is what I used 22 years ago. I bought the 90 drill just for the job. ...

Same basic thing I tried. Found a brand new 90 air drill on CL for $15 a few miles down the the road and it seems to work great (it may not last in a shop but for me it will last a lifetime). When I broke the 1/8 LH bit I tried a 1/8 RH bit. Since it did not seem to make a dent, I backed off for a while to investigate more. Besides, I need to fix the guide ( I found the .62" steel plate while bicycling one day a while back. You never know when you'll need such a piece. And that explains all the junk in my garage!). I think it is pretty soft steel.

[DMC5180]

Mine is mild steel (soft) , if I needed this for continued use. I would install hardened drill bushings in the pilot locations.


Dennis

[nkemp]

I was thinking of bushings as well. Thread them in and then change them as the bit size increases. Three, maybe four different bushing sizes. Then instead of that heavy chunk of steel (mine has some heft to it):
- Machine out the excess steel to reduce weight
or
- Use aluminum plate. Weld additional plate where the bushings would go.

I think if we tried, we could make it to service the top or bottom studs depending on how it is installed

A Include a 7mm stud remover/installer and we could make a traveling kit. The user supplies their own bits.

[DMC5180]

3/8 or 1/2 aluminum bar stock would be perfect with drill bushing.

No need for extra thickness, since the plate needs to be reversible for opposite orientation stud pattern.


Dennis

[David T]

3/8 or 1/2 aluminum bar stock would be perfect with drill bushing.

No need for extra thickness, since the plate needs to be reversible for opposite orientation stud pattern.


Dennis

I suggested removing the head as an alternative to removing the whole motor! I have been able to remove broken studs without removing the head (or motor) but if you mess things up beyond the limits of your abilities you can drag the head to a machine shop where they can finish the job. A drill guide is an excellent idea but if access if a problem that may only add to it and it prevents you from observing what you are doing. Because of the angles and difficulty it will help you stay centered on the broken stud. Especially if you do not have a lot of experience doing this kind of work. Patience is the key here. Work slowly and stop frequently to check and recheck that you are centered on the stud. The stud is steel and it is in soft aluminum, once you get off the stud you will quickly ruin the head.

[DMCMW Dave]

One other comment on this job - be extremely careful when drilling out the studs. The holes are blind, i.e. they do not go through anywhere. If you drill too deep, or get way off center, the lower holes will drill into the cooling system jacket (i.e. coolant will come out!). The upper holes will drill into the cam area, where the oil is. Neither is a good thing!

[nkemp]

One other comment on this job - be extremely careful when drilling out the studs. The holes are blind, i.e. they do not go through anywhere. If you drill too deep, or get way off center, the lower holes will drill into the cooling system jacket (i.e. coolant will come out!). The upper holes will drill into the cam area, where the oil is. Neither is a good thing!

One reason why drilling scares me more than welding a nut to the stud.

I measured my holes and they are about 22mm deep. It looks like my studs were in about 14mm. 8mm to spare (8mm is about 0.32 inches) My guide is about 16mm thick.

So:
- 22mm +16mm (38mm) of drill bit exposed beyond the chuck is when things get scary.
- 14mm +16mm (30mm) of drill bit exposed beyond the chuck may or may not break through the stud. Another mm or so should do the job.

So set the exposed portion of the drill appropriately. Or mark the drill bit with tape or a stop.

My engine leaks enough without drilling holes in it!

[DMC5180]

When it breaks thru the stud you'll know it. Just don't keep going. Put a depth mark on it or set the bit shallow. You can't go deeper than the chuck nose.


Dennis

[davidc89]

I talked to my machinist friend. I'm trying to convince him to make something.

[nkemp]

What are the torque specs for the nuts holding the exhaust manifolds to the heads? I see a few other things spec'd but not the manifold to heads nuts.

[DMC5180]

M7 X 1.00 torque spec is somewhat obscure in the shop manual. There is one reference I found for the timing cover bolts which states 11 ft lbs. I use that figure for all M7's.


Dennis

[nkemp]

That's what I'll use. It does seem a bit light but 7mm isn't all that big.

[DMC5180]

How did you end up removing the broken studs?


Dennis

[nkemp]

We tried drilling them but that wasn't going well. The extractor wouldn't bite. We were also getting a bit off angle. So Dave Conover welded a fender washer to the stud and a nut to the washer and they came out really easy. Using the washer made it easier to weld to the stud given the angle and lack of view. I made some aluminum fingers (aluminum flashing, drilled on one end, slotted on the other and bolted it to the opposite stud hole) to hold the washer in place while it was getting welded to the stud. Seeing those studs come out made my day! Thanks to David!!

[davidc89]

Yeah, welding it did the trick! It went really well actually. We tried drilling it first to see if it would have worked, as it is hard to drill after welding. Not so much luck drilling, but we didn't mess anything up!

[David T]

Yeah, welding it did the trick! It went really well actually. We tried drilling it first to see if it would have worked, as it is hard to drill after welding. Not so much luck drilling, but we didn't mess anything up!

Often when using the welding trick you can unscrew it with your fingers after it cools off. The heat from the welding helps to loosen it. Using the washer protects the metal nearby and gives you more to attach the nut to. Use Never-Seize when reassembling.

[nkemp]

The crossover pipe and the cat are all bolted in place. No real adjustments... just line up and bolt. The cat pipe seems open enough that the muffler pipe is bottoming-out as it should. But when putting the muffler back on, it seems that the Cat is about a half inch to the left (looking forward). Thus none of the muffler brackets line. Any suggestions?

I could cut a half inch off the muffler pipe where it goes in the cat. But I save those type modifications until all others are exhausted (pun intended).

BTW .... The muffler installation design is a mess to put it lightly. To remove the muffler, you have to take off all the brackets. Otherwise, to slide it out of the cat pipe you are pushing up against the brackets and vise-a-versa.

[nkemp]

Making progress. Took the muffler out and put it back in. It gave me a little bit more and I'm not sure where it came from. That muffler installation is a PITA.

Finally got it together (mostly). A couple 2x6 under the shoulder-blades for a little lift, the knee held the muffler up while I pushed/aligned the bracket that breaks with one hand and threaded like crazy with
the other. A little more tension on some of those brackets than I'd like but it is together. I sure hope the exhaust is quiet when I fire it up.

[nkemp]

Back together and running. All that is left is to drive it enough to burn off the penetrating oil. It is smoking like chimney right now.

Based on my NIST traceable butt, I'd say it runs better. So, per the original topic herein, maybe there was some blockage and HP loss. Or maybe it is just mental. Either way, it feels better.

A side benefit. I spent sooo much time using the tailpipes to maneuver the muffler into position that my greasy hands polished the tailpipes to like new!

[davidc89]

Glad to hear it is back up and running! Hopefully I can make it down for "Cars and Coffee" to hang out again. Maybe another Tech Day as well.