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Old 03-20-2011, 09:03 PM   #1
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Need immediate advice - stripped front engine mount yoke stud holes

Hi all,

Pulled my old engine mount out tonight and installed the new one. All was going well as I bolt the new mount up to the engine, tightened it, then lined up the yoke bolt holes with the matching holes on my 99 boxster's chassis.

I put 2 studs in no problem, tightened moderately with the nuts until it helped line up the others.

Put the next stud & nut in....tightened it....bam. Stud was tight and is now fully loose and pops out. Same thing happened with the one afterwards. Studs are slightly stripped and WILL NOT re-engage in the chassis. I spent 30 minutes trying to get them to re-thread, no luck.

What I need to know immediately is: can I take this to my mechanic and get him to tap out a new, larger (I'm guessing m12) threaded hole in the chassis and yoke?

Joe

P.s. Gently started and drove the car to test if I needed to flatbed it to mechanic - car drives fine with only 2 studs holding the yoke to the chassis. I felt safe with this considering how little real weight that front yoke carries. No ugly vibrations either.

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Old 03-20-2011, 09:27 PM   #2
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I am sure you can drive carefully to the shop.
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Old 03-20-2011, 09:42 PM   #3
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Thanks Andy, I'm confident in that too. I'm mainly wanting to make sure that new holes can be tapped into the yoke and chassis at that point. If not, I'm wondering about alternative solutions.

The boxster hadn't been started in 45 days and it absolutely purred to life within 1 second of twisting the key. Never started smoother than with this new engine mount
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Old 03-20-2011, 09:55 PM   #4
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One thing you can do is insert a Timecert - http://www.timesert.com/ .

These are pretty easily installed and are approved and used by Porsche.

They are plenty strong as this is Porsche's approved method of repairing stripped cylinder head stud taps on the block - if they can hold the cylinder head torques, they'll definitely work in this case.

Depending upon what you pay your mechanic, it may well pay you to buy a repair kit and do it yourself. Afterward, you can either add the tool to your toolbox - there are several other areas on the Boxster which benefit from timecert repair, or do what I did - get the kit, make the repair (in my case a stripped swaybar mount tap) and then resell the kit on eBay (I sold mine for the same price I paid, so essentially a free repair).

Cheers!
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Old 03-20-2011, 10:10 PM   #5
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Nice. Mechanic will probably charge me $50 for an hour of his time fixing this (it'll take him 30 minutes, but his hourly is so low it's great). He's a great guy - I've seen him fixing up $500 dodge caravans from the late 1800s and replacing oil pans on ferarris. Car's going in for an emissions and inspection anyway, so this is just gravy.

Really like that timesert stuff...a comprehensive kit (for more than one job) seems pretty expensive, but i'd order this for the future honestly next time this comes up. For now, I want my baby on the road....the weather is nice, insurance kicked back in on March 1st (3 months garaged rates), and it's time to start redlining again...

Joe
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Old 03-20-2011, 10:45 PM   #6
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I'm looking at replacing my motor mount this spring, and your problem is something I definitely want to avoid. In all the other threads I've seen on doing this job, I haven't seen this mentioned once. What exactly happened? Did you overtorque the bolts?
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Old 03-21-2011, 03:15 AM   #7
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Quote:
Originally Posted by Lil bastard
One thing you can do is insert a Timecert - http://www.timesert.com/ .

These are pretty easily installed and are approved and used by Porsche.

They are plenty strong as this is Porsche's approved method of repairing stripped cylinder head stud taps on the block - if they can hold the cylinder head torques, they'll definitely work in this case.

Depending upon what you pay your mechanic, it may well pay you to buy a repair kit and do it yourself. Afterward, you can either add the tool to your toolbox - there are several other areas on the Boxster which benefit from timecert repair, or do what I did - get the kit, make the repair (in my case a stripped swaybar mount tap) and then resell the kit on eBay (I sold mine for the same price I paid, so essentially a free repair).

Cheers!


These work very well, the key is to drill very perpendicular and perfectly square, like a human drill press, into the damaged surface.
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Old 03-21-2011, 07:01 AM   #8
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you'd need an M10x1.5 helicoil kit. you would drill oversized with a 13/32 bit, tap it with an M10 STI tap, and thread in the helicoil.

since you stripped not one, but TWO of these during your DIY, i recommend you NOT attempt this yourself, as you really only get one shot with these.

and yes, your mechanic may charge $50 an hour, but do do this yourself, you'd need to spend about $60 - $80 in tools & equipment anyway.


EDIT: BTW, this will take your guy 2-3 hrs
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Old 03-21-2011, 08:38 AM   #9
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2-3 hours? Good to know. I'll prepare for a $250 bill (including emissions and inspection).

I'm going to start another thread on this, but I don't think this was the original motor mount on this car. My boxster is a 99, and this motor mount was a solid-face design....according to Pedro's Garage, they stopped using those in 98. Further, the motor mount I removed was a 3 bolt design but MY CAR has 4 bolts in the updated design...the 4th bolt was unused on the motor mount. In addition, the 4th unused bolt that was in the engine was not of a design suitable for use on the motor mount - it wasn't long enough.

Based upon this stuff, I think this motor mount was put on the car sometime in the past and I think they over-torqued the studs back into the chassis.

One of the studs that I stripped out of the chassis was being tightened WITH a torque wrench to 34 lb/ft at the time it popped out.

So I think they were either over-torqued previously or were cross-threaded.

In terms of how to avoid any problems, here's what I learned:

1. Removing the lower coolant holes makes this entire job vastly easier. They are $10 a piece and if it's a good time to do your coolant, do this and replace the hoses simultaneously. It is good maintenance, and will probably save you an hour of frustration working around the hoses.

2. Get a 7mm socket and a 4-6" extension for it on a 3/8" drive (might need a 3/8 to 1/4 converter socket). Remove the studs with the mount, put the mount back on the engine, THEN thread the studs back into the chassis through the engine mount yoke holes. Once fully seated, THEN tighten the nuts on the studs and torque to value.

3. Have a 1/2 socket with a 6" extension and a 15mm socket for the nuts.

4. Buy a 15mm ratcheting wrench - it will make removing the mount from the engine far easier

5. Spray it all with PB Blaster before you start. The bolts may only be spec'd to 34 lb/ft of torque, but good lord are they tight when you are working on jack stands with small tools.

6. Doing the motor mount fits in well with several other jobs, including the aforementioned coolant but also the fuel filter. I'd recommend planning on doing several things at once to make it all alot more worthwhile....

7. The stock 987 motor mount is a great upgrade, but it's still really soft. You can easily twist it in your hands, showing you how much movement you'll get when an engine is hurled into a turn at high speeds. Consider going with a stiffened one unless you are really against vibrations in the cabin. I think a middle-of-the-road stiffened one would've been a wise choice for me.

Hope that helps

Joe
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Old 03-21-2011, 11:55 AM   #10
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No offense, but I don't think a helicoil is a proper repair for this. Helicoils require you drill an oversized hole in the piece and there's no real strength - it's essentially just a spring. Helicoils are notorious for coming loose (perhaps due to improper installation, but I've seen several fail). This isn't a stripped sparkplug hole, it will need to withstand some good forces on it.

The Timecert requires an oversized hole as well, but as it's basically a threaded bushing, it completely fills the hole providing great strength. And it won't pop out, it literally locks itself in place - the only way to remove it is to drill it out.

Also, it shouldn't take 2-3 hrs. to do the repair (not allowing for access, etc.). Watch the demos on the site, they are installed in under 30 secs. OK... by an experienced person, but that translates into minutes for an inexperienced one. And, they're using a cordless drill to drill the hole, the countersink and Timecert install. It's simple enough to hold the drill sufficiently perpendicular to the hole to do the repair. Watch the demos and see what I mean.

Yea, it may be a little spendy, but that's where it is. Plus, as I did, you can always re-sell the kit and get most if not all of your money back.

Cheers!
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Last edited by Lil bastard; 03-21-2011 at 12:03 PM.
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Old 03-21-2011, 12:14 PM   #11
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Quote:
Originally Posted by eightsandaces
These work very well, the key is to drill very perpendicular and perfectly square, like a human drill press, into the damaged surface.
+ 1 "the key is to drill very perpendicular and perfectly square"

The question here is, do you have enough room to position your drill in front of the engine..???
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Old 03-21-2011, 01:18 PM   #12
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Quote:
Originally Posted by Lil bastard
No offense, but I don't think a helicoil is a proper repair for this. Helicoils require you drill an oversized hole in the piece and there's no real strength - it's essentially just a spring. Helicoils are notorious for coming loose (perhaps due to improper installation, but I've seen several fail). This isn't a stripped sparkplug hole, it will need to withstand some good forces on it.
helicoils have plenty of strength if installed properly. the ones that come loose do so because of improperly prepared bores. generally, people don't use drill guides & as a result, the hole winds up being a little too large for the STI tap. the result is weak threads. a second mistake people make is not going full depth. they install a 10mm helicoil where the original bore was much deeper.

IMO a helicoil is fine here; the fastener is large & deep. it will need to be installed full depth, which is about 24mm. FYI, there is a steel threaded insert in the car's body; this is what you'll be drilling into. USE A DRILL GUIDE. USE LUBRICANT ON THE TAP & ON THE DRILL. (boelube is the best lubricant to use here, btw)



Quote:
Originally Posted by Lil bastard
The Timecert requires an oversized hole as well, but as it's basically a threaded bushing, it completely fills the hole providing great strength. And it won't pop out, it literally locks itself in place - the only way to remove it is to drill it out.
time sert is a great product. in steel, this is overkill. in aluminum, it's an excellent solution, especially where the primary stresses are strain rather than shear. (most here will be shear). again, installation technique is very important.

Quote:
Originally Posted by Lil bastard
Also, it shouldn't take 2-3 hrs. to do the repair (not allowing for access, etc.). Watch the demos on the site, they are installed in under 30 secs. OK... by an experienced person, but that translates into minutes for an inexperienced one. And, they're using a cordless drill to drill the hole, the countersink and Timecert install. It's simple enough to hold the drill sufficiently perpendicular to the hole to do the repair. Watch the demos and see what I mean.
the point of providing a duration was to allow the OP to get a sense of his cost to have this done. the 2-3 hours includes TOTAL time to do the job, which obviously includes lifting the vehicle, draining the coolant, removing the hoses, removing the mount, prepping the bore, & installing the repair. i have done many of these; plan for more than 30sec.
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Old 03-21-2011, 01:34 PM   #13
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I stripped a head bolt on my buddies BMW K-1000 will going through the torque sequence to the letter....So I can sympathize. We used a helicoil and didn't like the feel of it. The fit of the thread was quite sloppy. My guess the drill wandering around made the hole more over sized than it should be never mind geometrics. The bolt did develop full torque though. I didn't know about timecert until now.
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Old 03-21-2011, 01:39 PM   #14
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Heliocoils are no match for a timesert. Heliocoils amount to jamming stripped threads with wire till it binds together and holds. A timesert actually places a new threaded receiver into the repair. When executed right it even looks like factory as the threads are brand new. as for the other question of room to drill, in a case like this you might have to eat the cost of a right angle drill and chalk it up to incredible savings over having someone else do the repair.
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Old 03-22-2011, 05:19 AM   #15
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Insite,

****************....thanks for posting that. I completely forgot that he's going to need to remove those hoses now to get adequate access and, knowing him, he'll want to replace the hoses since they are old, worn, and off.

Because of you, and rightfully so, I just went on pelican parts and ordered the coolant hoses, another gallon of coolant (brings my stash to about 9 quarts of coolant), and a few other miscellaneous parts I needed.
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Old 03-22-2011, 06:01 AM   #16
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P.s. Gallon of coolant is cheaper at the porsche dealer and doesn't cost as much to get shipped overnight (because its local). Stopping byt he porsche dealer today to pick up 2 gallons

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