Passenger side motor mount threads slightly off center....need assistance please! - PeachParts Mercedes-Benz Forum

HuskyMan · #1 04-09-2018, 11:00 PM

The driver's side motor mount bolt goes in fine, the passenger side motor mount threads are slightly off center.....the bolt goes about half way in then becomes difficult to turn using a wrench. Question, if I start the engine, will the vibration help to line up the thread holes?

tangofox007 · #2 04-09-2018, 11:25 PM

Just give the engine a shove in the right direction. Show it who the boss is.

Next time, just disconnect one mount at a time.

BillGrissom · #3 04-09-2018, 11:40 PM

Do you mean the top two bolts (6 mm allen) or the single bottom bolt (8 mm allen)? Either way, insure you aren't cross-threading the bolt. Leave the 2 top bolts loose until you get the bottom bolt started. You will likely need to pry the engine around w/ a crow-bar and perhaps loosen the 2 tranny mount bolts. I just did this 1.5 weeks ago, and it is never easy.

HuskyMan · #4 04-10-2018, 09:15 PM

Found the 12.9 grade M10 1.5X40 bolts but am having trouble locating the structural matching washer. Finally went to the stealership, they want $26 for the bolt which comes with the washer. It has to come from Germany. so.....checking out a local hardware store tomorrow to try and come up with a solution.

I did purchase a cheaper grade M10 1.5X40 bolt which I am going to convert to a thread chaser. Question, should I use some type of oil on the thread chaser? I was thinking perhaps 3 in 1 oil or cutting oil like is used on chain saws?

Junkman · #5 04-10-2018, 09:36 PM

Buy the correct tap if you need to clean the threads. I bought a cheap HF set a while back that is poor quality but works most of the time. I fill in with what isn't included in the set.

Some place like Ace Hardware may have a washer. Lowes etal may have one in the specialty section. Lots of places online will have the washer.

leathermang · #6 04-11-2018, 10:55 AM

Yes, buy the correct thread chaser and use heavy grease on it.... go in a little at a time.. back out and clean and regrease the threads... until you have a good set of threads remaining...

tangofox007 · #7 04-11-2018, 11:25 AM

Quote:

Originally Posted by Junkman

Buy the correct tap if you need to clean the threads.

Taps are designed to cut new threads. Repairing existing threads is best accomplished with an appropriate thread repair tool, especially when dealing with an aluminum alloy like an engine mount arm.

HuskyMan · #8 04-11-2018, 05:19 PM

I easily sourced grade 12.9 M10 1.5X40 for the motor mounts. This chart shows an even higher grade, A-2. There wasn't one specialty fastener supplier in town that had them.....I'm thinking an aircraft/spacecraft parts house????

https://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx

Diseasel300 · #9 04-11-2018, 05:57 PM

12.9 is the highest strength bolt you're going to find. The A2 is a specialty bolt. Look at the strength data in the chart you posted. It is NOT a strong bolt, even weaker than the 8.8 grade.

tangofox007 · #10 04-11-2018, 08:39 PM

Quote:

Originally Posted by HuskyMan

[SIZE=2]I'm thinking an aircraft/spacecraft parts house????

Aircraft fasteners are almost universally SAE.

Simpler=Better · #11 04-11-2018, 09:29 PM

Unless it's a drag car with a superpump a grade M8.9 (aka SAE grade 5) will be just fine.

HuskyMan · #12 04-12-2018, 10:01 PM

Looking at the chart, the tensile strenght of an A-2 bolt is lower than the 12.9 bolt. Apparently, stainless steel is not as hard as the 12.9.

MagicBus · #13 04-15-2018, 10:37 PM

I'm currently dealing with the same exact problem on a 1983 240D. I disconnected both mounts for replacment. The driver's side bolt goes in easily, but the passenger side bolt goes in about halfway and hangs up. I didn't have any trouble removing the old bolt, so I don't think there's a problem with the threads in the engine support arm.

I'm going to keep playing around with it without forcing the bolt in. That just feels like a bad idea to me.

I may loosen the smaller mount-to-body bolts to see if the mount itself has enough wiggle room to compensate for this. Does anyone know if I can tighten the smaller bolts with the engine bolted in place?

Simpler=Better · #14 04-16-2018, 10:43 AM

If you think the threads are toasted, make a thread chaser from an old bolt and clean them.

As for alignment, get creative with ratchet straps and wood blocks. You can line it up, it just takes patience.

leathermang · #15 04-16-2018, 11:19 AM

Quote:

Originally Posted by Simpler=Better

If you think the threads are toasted, make a thread chaser from an old bolt and clean them.

As for alignment, get creative with ratchet straps and wood blocks. You can line it up, it just takes patience.

There are professionally designed and executed Thread Chasers...
HOME MADE ones are likely to make the situation worse...

AND as to pulling and forcing the engine into a POSITION which allows the bolts to be screwed into the WRONG engine mount..

I suggest that may invalidate the proper function of our engine mounts....