TheSamba.com :: View topic - STRIPPED exhaust bolt on #3 cylinder

Thu Jun 05, 2008 10:10 am

I noticed some soot around the #3 exhaust flange (passenger side towards the front) and the culprit is the hole is stripped out and the bolt won't tighten. The #plug is sooty and I have been having weird running issues so I am assuming there is a relationship here.

Anyway, I've never had to address this before. Do I tap the hole for a bigger bolt? Do I use a slightly bigger stud and force it in? I've heard of timcerts and helicoils but that seems like a tricky procedure for a lunkhead like me.

I am willing to take the easy way out plus the VW place near me wants $300 to do the job! Can you dig that?

THANKS!

Thu Jun 05, 2008 10:55 am

There are stepped exhaust studs available that are M10 on one side and M8 on the other. I've read good and bad about helicoils.

The hardest part about doing the job is accessability. At the very least a right angle drill will be required. Hopefully you don't have to drop the motor.

Thu Jun 05, 2008 11:05 am

The one option I would not do is force a bigger bolt in.

I know just enough about tapping threads in an engine block (which is very little) to know that something like that is well worth paying to know it's done right. $300 does seem on the near edge of pricey, but may be worth it to prevent bigger headaches.

My old '71 bus had an insert for one of the plugs and it worked just fine.

Thu Jun 05, 2008 4:19 pm

Yellow Rabbit wrote: There are stepped exhaust studs available that are M10 on one side and M8 on the other. I've read good and bad about helicoils.

Awsome! Where have you seen these?

Thu Jun 05, 2008 4:27 pm

Maybe this will work, the stud is M9->8 stepped

http://www.germansupply.com/home/customer/product.php?productid=17388

A stud on my '78 stripped out last week and the metal is so bad and flakey around it that my mechanic doesn't think an insert will hold. Hopefully that is not an issue for you. AC motors run alot hotter heads than WBX so more metal fatigue should be expected. Bad news is that means a new cylinder head for me, or a rebuild which is how I'm going.

Thu Jun 05, 2008 4:55 pm

The M10-M8 studs are available through some local auto parts stores. My local one said they are only available if you order a box of 10 as I recall. The entire box was about $18.

Thu Jun 05, 2008 7:19 pm

I had this happen to me, almost exactly.
I had soot around an exhaust port, form an exhaust leak, and being scared of exhausts at the time, paid the shop i was working at to repair it.
We agreed upon two hours labor.....About $120. (Plus gaskets). Well they put it off and put it off, untill i nagged and nagged, and when they put the thing up on a lift and got in there, they managed to break off one of the studs in the head.
Well, now we run into the same problem you're dealing with, accessability. They pulled out there professional tools and "skill", and with a right angle drill, tried to drill out the stud. Then, the titanic moment......
The drill bit broke off. Just like the titanic hitting the iceberg, i was sunk.
The problem was, as they told me, you cannot drill out a drill bit.....
So for weeks the bus sat, untill some magic bits arrived, and they were "able to fix it". It cost me about $700 total. And, the fix only lasted 100 miles. (They drilled crooked and i ended up having it drilled properly and helicoiled while i had the heads off for my rebuild).

So long story short, i sincerely encourage you to pull the engine, or at least that head. I really do. It SUCKSSSSSS when you screw it up.

I'm now using stainless steel bolts all around, and its GREAT. I pulled the exhaust again the other day in under an hour!

Thu Jun 05, 2008 7:58 pm

Unless you have a UK setup, the "passenger side front" cylinder is not number three........it is number one.

I have repaired that condition in the past with the engine in place, using a helicoil insert. You can get the right size at your nearest Harbor Frieght or other tool outlet. You need a drill of course, and probably half a day or more if it is your first; as well as standard tools, jack, stands, etc.

I wouldn't suggest ruining the head with some oversize approach.

Thu Jun 05, 2008 8:01 pm

I recently used Timeserts for the first time on several different aluminum engine parts. Even though the kit is expensive I won't hesitate to buy a different size kit again. Very nice little tool to have. The cheapest I could find them was at Wurth USA ($100).

Thu Jun 05, 2008 9:08 pm

Timeserts are it. Only thing I would use for this sort of repair.

When you have a broken stud, it helps a lot to get a center drill, for lathe work. They're cheap at HF. Grind the stud flat if it's exposed. Center punch it, accurately. Make a hole with the small center drill, which leaves a 60deg. angled hole which a slightly larger regular drill will center in. Work your way up, not more than 1/16" at a time, and you can slowly remove all the steel, if you're careful and start on center.

Thu Jun 05, 2008 10:09 pm

tencentlife wrote: When you have a broken stud...

No, no! Thank gawd I don't have a broken stud! I'd just shoot myself if that were the case. The bolt has stripped out the hole. The head, as far as I can tell from the P.O.'s paperwork, was a head reworked by a shop somewhere in Ohio. I assume the hole was stripped out then.

Fri Jun 06, 2008 11:11 am

otiswesty wrote: Maybe this will work, the stud is M9->8 stepped

http://www.germansupply.com/home/customer/product.php?productid=17388

A stud on my '78 stripped out last week and the metal is so bad and flakey around it that my mechanic doesn't think an insert will hold. Hopefully that is not an issue for you. AC motors run alot hotter heads than WBX so more metal fatigue should be expected. Bad news is that means a new cylinder head for me, or a rebuild which is how I'm going.

This timesert kit looks like a perfect solution.

I had this issue on an air cooled head before the days of timeserts. I made a custom stud by drilling out a larger bolt, brazing a stock stud into it, then drilling and tapping the head for the larger bolt. The fix worked great, and never failed, but it was time consuming to do.

The m10-m8 idea is the same approach, and should work fine as long as you do a good job of drilling and tapping to assure a solid hold.

Sat Jun 07, 2008 7:45 pm

You might be in luck since you say it is a capscrew (bolt) which has stripped the tapped hole and not a stud. The hole for the exhaust flange fastener is 25-30 mm deep with only a little more than half of it having fully formed threads. Although the capscrew has wasted the threads which it engages near the top of the hole, there is a large portion of the hole towards the bottom which is unscathed.

So, you may be able to fully thread the hole to its bottom with a blind tap and create enough new threads to securely retain a stud.

Here's a basic game plan:

Remove the capscrew measure its length and subtract the thickness of the exhaust flange+flange gasket. This will tell you how much deeply the capscrew went into the hole. Then, using some manner of depth gauge, measure the depth of the hole so that you know where its bottom is. While it is nice to have, you don't need a micrometer depth gauge for this just some way to fairly accurately establish the hole depth.

Now, take an 8X1.25 mm BLIND tap and mark it (for example, wrap it with masking tape) at the hole depth you measured. Then, tap the hole to the depth you have measured. Use some type of cutting fluid for aluminum on the tap. I've tried bunches of them and on aluminum lowly kerosene is as good as any of the high tech stuff. As you advance the tap into the hole, back it out a full turn for every couple of turns you go in. This will "break" the thread so that the tap doesn't become clogged with the cuttings and snap off. I once heard an old timer say that more taps a snapped off backing them out of aluminum than ever in tapping steel.

What you are doing is considered deep hole tapping because the depth of the hole is greater than 1 1/2 times its diameter, so, proceed prudently. As you are tapping the hole, you will develop a sense for how much torque it is taking to cut the new threads. This is important because as you approach the bottom of the hole, as indicated by the marking you put on the tap, you will obviously want to stop at the bottom without braking off the tap. When you have reached the bottom of the hole and the tap seems to be taking more input than before, stop. Back out the tap, flush out the hole and run the tap in and out a few times ending with a thorough flushing.

Get or make a stud which is long enough and thread it into the hole until it bottoms out. Cinch up the exhaust flange with a nut.

The rule of thumb is that a tapped thread length of 1 1/2 times the diameter of the fastener is enough of a thread to take the maximum torque for that fastener. Since the torque for the exhaust flange capscrews is specified at only 15 ft-lbs, even if you only get 6mm of fresh threads the flange will be secured.

The one time I did this repair I removed the header, but I think it can be done with the header in place.

This is what I would try before I go to a helicoil or thread repair insert. And, in my opinion, a keyed thread repair insert will wipe the ass of a Timesert without the ridiculous expense of the dedicated tooling required to install a Timesert. But, that's a story for another time.

Rich

Sat Jun 07, 2008 9:58 pm

Your right on the money with this repair scenario Richy.

I'd also run a blind tap to the bottom, and grab what ya can-

The only addition to your advise is I'd soak the threads of the new stud with LocTite prior to running it home.

Just in case it decides to try & wiggle loose again--it'll stop that program in a heartbeat.

Sun Jun 08, 2008 7:34 am

RicoS's method is exactly how I fixed mine except that I left my manifold in place. It's been holding strong for three years now.

I agree that Timeserts are the ultimate fix, but I also have no complaints about the method I used.

Sun Jun 08, 2008 8:55 am

Terry Kay wrote:
The only addition to your advise is I'd soak the threads of the new stud with LocTite prior to running it home.

Just in case it decides to try & wiggle loose again--it'll stop that program in a heartbeat.

Thanks for keeping me honest, TK. Since, as a cop once said as he guided me into the back of his cruiser,"You always have to have the last word, don't you?", I have to add one thing. Just be careful of how much LocTite you slather on the stud so that you don't end up with a bunch of it sealed in the bottom of the hole and keeping the stud from reaching its full engagement.

Rich

Sun Jun 08, 2008 9:01 am

OK Brodrick Crawford---

Carefully add a few drops of stud & bearing mount LocTite to the threads of the stud prior to running it down home.

22-50 bye---

Wed Jun 11, 2008 9:21 am

After considering all of the great advice here I went with a SS 10mm bolt and nut. I looked everywhere in Austin for step-studs and that came up zero. I had to enlarge the flange hole a little bit to accomodate the new stud.

I had never tapped anything before so this was definitely uncharted territory. I went to Sears and got the best drillbits I could afford ($75 bucks, if you can dig that) and the best tap set I could afford. I don't know much but I do know that cheap bits break off. Ask me how I know.

I did a few test-taps on some scrap metal just so I could get a feel for how this was going to work. A 500-dollar cylinder head is a bad place to train yourself at metal working. The best threads came from making sure the hole was a small as I could get away with withough getting the tap stuck.

The orignal hole was 8mm and the new one 10mm. I drilled out the hole only a little bigger than 8mm to roughly 9mm. I found out that the tapping process is slow. Very, very, very slow. At first I used 3-in-one oil as my cutting oil but I found that PB Blaster seemed to work a lot better and it can be shot into the hole as I was working

As for the tapping itself, I would go 1/4 turn to cut, half a turn back to clear the chips, then forward a half turn to get to the new cut, and then a 1/4 turn to make the cut and so on. After 2 full turns I would back the whole thing out and clean out the chips from the hole with brake cleaner and more PB Blaster.

For me it was a very difficult job because if I screwed it up, there would be a much tougher and more expensive job waiting for me!

Anyway, great advice and encouragement here from you guys. THANKS!!!!!!!!!!

Thu Jun 12, 2008 5:05 am

deprivation wrote:

. . . I went to Sears and got the best drillbits I could afford ($75 bucks, if you can dig that) and the best tap set I could afford. . .

I did a few test-taps on some scrap metal just so I could get a feel for how this was going to work. A 500-dollar cylinder head is a bad place to train yourself at metal working. The best threads came from making sure the hole was a small as I could get away with withough getting the tap stuck.

. . . At first I used 3-in-one oil as my cutting oil but I found that PB Blaster seemed to work a lot better and it can be shot into the hole as I was working . . .

Anyway, great advice and encouragement here from you guys. THANKS!!!!!!!!!!

Dep,

I congratulate your pluck on persevering through unknown territory. I have a few words for the next time you, or others, have to go through an exercise like this.

First, avoid Sears. Instead, find an established industrial supply house to buy your tooling and hardware. The guys behind the counter there might not be as affable or pretty as a clerk at Sears, but their knowledge will make up for that and even the gruffest of them will have pity on you. Also, an industrial house will sell you the good stuff at a competitive price; they can't afford not to.

There is no need to decide on which size tap drill you need for a particular tap by experiment. Just look it up on a tap drill chart which you can find almost anywhere, nowadays or, at an industrial house, tell the counterman you need a tap drill to go along with the tap you are buying. He'll keep you honest. Also, some commercial grade taps have the tap drill size stamped right on the shank.

Lastly, since aluminum is soft, some guys think it can be tapped with any cutting fluid. But, any experienced machinist will say that aluminum is "gummy" and it is its "gumminess" which snaps off taps. As you found out, some cutting fluids will stop a tap cold in aluminum. As I said before, you can spend a lot of money on cutting fluids dedicated for aluminum but few perform noticeably better than kerosene.

I'm glad you didn't have to write a post entitled "How Do You Remove a Broken Tap?".

Rich

Thu Jun 12, 2008 10:00 am

RicoS wrote: I'm glad you didn't have to write a post entitled "How Do You Remove a Broken Tap?".

God - ain't that the truth!