mowgli29

iTrader: (21)

Hey guys...bit of a problem.

I'm going to be installing ES motor mounts...but I know that the holes for the bolts holding on the lower crossmember are all F'd up! Once it comes off, it's not going back on without re-threading/helicoils.

I got two new bolts for the lower crossmember, I'm just not sure on the thread pitch. I went to ace, but couldn't figure it out 100%. Because of the bolts' design, I couldn't use the board full of sizes to figure it out. So I just started using nuts.

Well a 1/2-20 seemed to fit, but it was a bit loose. Then I found a M12x1.25 and that went on perfectly! But, then I pulled another one out of that bin and it wasn't close...so I have no idea of the actual size of the nut that fits...

I'm leaning towards the M12x1.25 for the thread pitch, but it would be nice if someone could confirm.

Also, how long do the heli-coil inserts need to be? I found a M12x1.25 kit with inserts that are 18mm, but I don't know how close that will be. I'm thinking I should measure the length of the threads on the bolt and look for inserts that are a tiny bit shorter.

Will the helicoil kit tell me what size drill bit I need?

Any advice?!

irish44j

iTrader: (38)

my advice: heli-coils are not really that strong for an application like this. A better idea would be to go to the next size of bolt up, and drill out the hole and re-tap it for the larger bolt. This is what I did for the rear control arm bolts that I stripped out. I don't know if they are the same size, but those were 12x1.25 as well. I drilled them out to a 14x1.5 bolt (got the tap, bit, and bolt from McMaster-Carr).

mowgli29

iTrader: (21)

That was my original idea, but I wanted all four bolts to remain the same as each other. Yeah I'm **** like that..

I had always read that helicoils were REALLY strong! Are you saying that while the threads may be more resistant to damage, the insert itself may pull out? In what way are they weak?

Perhaps I'll just drill and tap to a bigger size...

Would you recommend drilling and tapping only the holes that REALLY need it? I know one hole does, another will probably need it in the future, and the two fronts are fine. Should I just do one for now? I'm just worried this will always haunt me no matter how I "fix" it.

Cutler

iTrader: (3)

Go up a bolt size as Joshua has said....

mowgli29

iTrader: (21)

my names josh too

I guess I'll do that then...think I should do just the hole that REALLY needs it, or should I do both and get it over with?

Oh and hey Josh, any idea what size drill bit you used for the M14x1.5?

And wouldn't I have to have some sort of a sleeve over the bigger bolt for the bushings?

irish44j

iTrader: (38)

Helicoils are pretty strong, but for such an important weight-bearing piece as the crossmember I would be hesitant to use them. Besides, you can get stronger bolts than those stockers anyhow....Also the point that helicoils do not always go in easily and you don't tap just right, it could get stuck halfway in and be a REAL ***** to get out. Trust me, I've used helicoils alot...it happens and is extremely frustrating.

To helicoil the holes, you're gonna essentially drill them out to 14mm, tap them to 14x1.25 (or thereabouts), and insert the helicoil anyhow, to get the original thread back to 12x1.25. So if you're going through all that effort, might as well put bigger, stronger bolts in.

I would only do the ones that need it. tapping big holes like this is a major pain in the ***, especially on your back under the car. And also make sure you use a cutting oil so you don't snap off the tap!

irish44j

iTrader: (38)

The bit I used was a 37/64. Be careful when you order the bit to make sure that the non-cutting end will fit in your drill! The bit I ordered was too wide at the base and I had to grind it down to fit in the drill. Larger industrial drills might have enough clearance, but my mid-grade DeWalt didn't.

If you order a tap from McMaster, it will tell you on the site what size drill bit to use with it, though.

You won't need a sleeve for the bushings, though you might have to "drill out" the bushing as well for the bolt to go through them. The bolts I did are not bushed, so I didn't have that issue.

irish44j

iTrader: (38)

of course, your other option (and I don't know if this is possible or not since I haven't looked at those bolts in a long time) would be to simply put a nut and big-*** washer on the backside and not worry about helicoil or rethreading.

I'm not sure if there's access to the backside, though. Just throwing the idea out there.

Matt93SE

iTrader: (44)

Actually, heli-coils are usually stronger than the original threads in many cases like this...
the tensile strength of the spring is much greater than that of a nut that's welded into place (killing its heat-treatment). so in essence you've got the advantage of the larger thread tapped into it since that's now the weakest link, but you can use the original bolts. Plus the threads on the helicoil will lost much longer than the ones in the regular nut. stronger metal means you can pull them out more often without wearing the threads out.

(There's a damn good reason most race engine head bolt holes are drilled out and helicoiled...)

irish44j

iTrader: (38)

Aren't race engines helicoiled so that they can be retorqued multiple times into the aluminum head/block during rebuilds? I don't know that it is necessarily a holding strength issue, it's the matter of reducing wear into the aluminum by having the friction surface of the helicoil thread to the bolt "protect" the head/block, if you will....

My two sets of race skis are entirely helicoiled to strengthen the binding mounts as well, it's a common practice.

That all said, I still think for his situation, with the difficult tapping position and th additional difficulty in precision threading a helicoil into such a mount, he'd probably be better off just rethreading the hole/bolt.

Just my opinion, though....

mowgli29

iTrader: (21)

One thing I have going is that I'll be on a lift at a Nissan stealership...this way it'll be ALOT easier to install everything as well as drill/tap new holes. With this in mind...I might just do both rear ones now, and that might warrant using the helicoils.

Also, I would rather use the stock bolts, just because they're not a typical off the shelf bolt...they look like Nissan designed them for the job they do. To me, it looks like the "sleeve" on the stock bolt is still a larger diameter than a 14mm bolt will be so I might still need some sort of sleeve for between the bushing and new bolt. I think the built in "sleeve" on the stock bolt is there to help prevent over-tightening too. It would just be nice to re-use the stock bolts IMO.

Also, what Matt said about helicoils is what I've always heard. But, even if they aren't any stronger than stock holes, they HAVE to be stronger than the three and a half bolts in there now! One bolt is honestly 1/3 of the way out, but I'm afraid to try and tightnen it because I know the threads are F'd! (BTW, it's been like this since december...)

mowgli29

iTrader: (21)

Just for reference...here are some pics of the OEM bolts and the ES bushings waiting to be installed with them. Now you can see the "sleeve" I keep talking about.








I guess I could call it a "shoulder" not a "sleeve." Either way, it looks like its there to stop the bolt and keep it from being over-tightened. Maybe

irish44j

iTrader: (38)

yeah, ok that's a shoulder bolt. I forgot they looked like that. You could probably order some with a different thread and the same size shoulder but at this point helicoil may be the easiest way to go.

mowgli29

iTrader: (21)

I was thinking along the same lines there. My only remaining concern I guess is the length of the insert.

Should I just measure the threads on the bolt and find a helicoil insert close to the same length? Would it be better if the insert is shorter or longer than needed? I'm thinking shorter to avoid the insert protruding from the original hole.

mowgli29

iTrader: (21)

Ok well I just now got around to ordering a thread repair kit. I found "perma-coil" kit on ebay for $20 bucks and jumped on it (link). It doesn't have a drill bit with it, but I already have two of the proper sized bits (31/64), so that doesn't matter.

The kit has 18mm long inserts. I could also find 24mm inserts, but I believe that would be too long...

I'll most likely go to the stealership friday or saturday to do the install. I'll let you guys know how it turns out. Maybe I'll take some pics too.