Author Topic: Motor mounts again (Read 4636 times)

dirkbalter · « **on:** January 17, 2020, 00:39:32 »

Hello all,
I am re-assembling my new motor mounts. I purchased the motor mount kit as well as new bottom plates with the bolt that has a big washer attached to it. This is a replacement kit for the earlier style motor mounts. My BBB does not cover this style.
I red somewhere here, but can’t find the post anymore, that the (lower) bolt (item # 6 in the diagram) needs to be screwed into the motor mount until the thread bottoms out and locks.
Can anyone confirm that this is correct or otherwise advise on the correct assembly procedure?
Thank you

WRe · « **Reply #1 on:** January 17, 2020, 08:48:10 »

Hi,
I assume you mean the "later" style mounts (230Sl-280SL from 012865) otherwise I misunderstood your thread but there is nothing special mentioned in workshop manual.
...WRe

dirkbalter · « **Reply #2 on:** January 17, 2020, 16:14:06 »

WRe,
thank you for the pages from the later workshop manual. Yes, I meant later style. The once that came off my car didn’t have the bottom plate or the rubber cone washer. I bought new ones and wanted to make sure these don’t need any pre-load or special set up. (Compared to the earlier 230’s)

ja17 · « **Reply #3 on:** January 17, 2020, 17:18:46 »

Yes, the special bolts screw in until they bottom out. Make sure the plate has it's "bulge" upwards.

dirkbalter · « **Reply #4 on:** January 17, 2020, 19:05:24 »

Joe, thank you. “Bulge” up is what I have.

Harry · « **Reply #5 on:** February 06, 2020, 13:18:50 »

The BBB has a modification in this section that specifically addresses the 230SL. Seems like it says to tighten the lower bolt to a point where it is tight, then place the mount in a vise (or otherwise) and compress the mount such that there is then a gap between the washer on the bolt and the rubber "doughnut". At this point the bolt is run down just far enough to close that gap, and the unit is removed from the vise. The point appears to be to avoid having the doughnut under a lot of compression and torque while tightening the bolt to achieve the right amount of pre-load in the mount.

BTW - my lower bolts have an integral washer, i.e. it is part of the bolt.

Thoughts?

Harry

dirkbalter · « **Reply #6 on:** February 06, 2020, 15:57:36 »

Hey Harry,
Me again. I believe you have (like me) the later style mounts. These only get bolted until the bolt (with integrated flange) bottoms out. As described by Joe A. above.

Harry · « **Reply #7 on:** February 06, 2020, 16:50:38 »

Yes - I have exactly what you have in the photo. So the BBB is referring to the earlier style? When you bottom the lower bolt out, is it touching the rubber doughnut? Compressing the doughnut? Or is there a gap?

Thanks very much,
Harry

dirkbalter · « **Reply #8 on:** February 06, 2020, 17:46:29 »

Harry,
no gap. It is compressing them a bit.

Harry · « **Reply #9 on:** February 06, 2020, 18:51:03 »

Thanks. That's good to know.

PeterPortugal · « **Reply #10 on:** February 06, 2020, 20:01:36 »

Guys,

I am at the same point with my mounts and my concern is there is little to stop the bolts coming loose unless you tighten them up a bit.

Anybody got a rule of thumb which can be applied such as finger tight (is this bottoming out?) and then two complete turns with a spanner??

Any advice appreciated.

Peter

Harry · « **Reply #11 on:** February 06, 2020, 20:48:18 »

Peter - if you look at the pictures of the lower bolts, they are shoulder bolts. They bottom out because they run out of threads and the shoulder is forced against the support. I think you can tighten them plenty tight enough to not worry about them coming loose. They are 12mm 1.5 (I believe) so it would take some torque to damage them.

dirkbalter · « **Reply #12 on:** February 06, 2020, 21:17:10 »

I will in any case add some thread looker (Loctite blue) to the bolts.

PeterPortugal · « **Reply #13 on:** February 06, 2020, 22:19:50 »

Harry,

Thanks....should have been obvious to me.

Thread locker is probably a good idea too Dirk

Thanks

Petet

PeterPortugal · « **Reply #14 on:** February 07, 2020, 15:18:17 »

Guys,

If I tightened these bolts until they bottomed out it would compress the rubber washer very substantially.

I bought repro bolts as they were easily available. I am worried that dimensionally they may be different to the originals.

The bolts are about 55m from under the washer to the end of the shank. 29mm threaded, 26mm plain. If you have yours still readily available could you cross reference?

I have attached a picture showing a mount with the rubber washer fitted. I have compressed this by tightening the bolt by hand as much as I can and then 2 full turns with a spanner. The other mount has no rubber washer and the bolt bottomed out. As you can see it has to go in a lot further and would compress the rubber washer a lot.

Regards

Peter

dirkbalter · « **Reply #15 on:** February 07, 2020, 15:21:42 »

Peter
I will get back to you tonight showing my set up and dimensions.

PeterPortugal · « **Reply #16 on:** February 07, 2020, 15:54:24 »

Thanks Dirk.

I worked out that hand tight + 3 more turns would give me a dimension "a" of 14mm as per the BBB fig 22-1/1 for the 190C which uses the same hardware. This feels about right.

Peter

dirkbalter · « **Reply #17 on:** February 08, 2020, 16:17:36 »

Hi Peter,
My bolt length is 54.5 from underneath the washer. The actual thread length is no more than 22mm. Once the flange hits the rubber, I have approximately 3 ½ turns until the thread bottoms out and locks.
The picture shows the bolted down state.

PeterPortugal · « **Reply #18 on:** February 08, 2020, 19:05:44 »

Hi Dirk,

I really appreciate your feedback. I will stick with my plan of going for "a" = 14mm which ties in nicely with your finding of 3.5 turns from touching the rubber until the screw bottoms out.

This just goes to show that repro parts are probably best avoided. I also note that your washer seems to fit into a recess so it is flush. Mine sits on the top of the rubber.

I bought some original motor mounts and comparing them next to the Meyle versions they look much higher quality.

Onwards and upwards now !!

Regards

Peter

dirkbalter · « **Reply #19 on:** February 09, 2020, 18:30:46 »

Peter,
Thank you, we are learning together here. I just recognized something else. When my lower flange bolt bottoms out, the “a “dimension you are referring to from the early BBB is approximately 8mm in my case.

I also measured the available clearance for the upper bolt that holds the aluminum motor mounts. I only have 13.4 mm left (see pic). The aluminum mount thickness measures 36mm. the (upper) bolt is 50.5 mm long. The spring washer is approx. 1mm. That would require 13.5 mm clearance from the top of the mount before the face upper bolt hits the face lower bolt.
Bases on that, I am revising my plan of just bottoming the (lower) bolt out and will instead ensure that I have approximately 2-3 mm clearance between the bolt faces once installed.
Let me know what you think?

PeterPortugal · « **Reply #20 on:** February 09, 2020, 20:29:45 »

Hi Dirk,

The issue you describe is exactly why I asked my questions.

If I had "bottomed out" my "lower" bolt the upper bolt would not have engaged fully until they clashed.

My car (and I think yours too) didn't have any of this hardware fitted previously so we have to be improving the situation !

How did you measure the "a" (8mm)? From the upper face of the washer to the yellow zinc plate?

Regards

Peter

dirkbalter · « **Reply #21 on:** February 09, 2020, 23:29:47 »

Peter
Yes, from the upper face of the washer to the yellow zinc plate. I just put a small ruler across the face of the washer, measuring the distance with calipers. Not super precise but good enough for what I am looking for.
Yup, PO or shop removed the additional hardware from my car and only installed the motor mounts by itself. Nevertheless, our set up is used on the later 230-280 sl’s and is the recommended and I believe the only available replacement by MB right now.

BTW, I also checked and WRe above confirmed that there is no special set up described in the later BBB.

If I set the "a" dimension to 13-14mm as you suggested earlier, the lower donut is still compressed and I have sufficient clearance between the bolts. Unless someone has a better suggestion or intel, I will set the lower bolt with Loctide to prevent accidental loosening to this dimension and forget about it?

PeterPortugal · « **Reply #22 on:** February 10, 2020, 10:04:45 »

Dirk,

I have done exactly as you describe and mine are already fixed with thread locker (blue, non permanent...just in case).

It would be good to get some more feedback from some of the posters who suggested bottoming the bolt out as they are undoubtably experienced. I think it would have been a bad idea with my repro bolts (purchased from the SLShop for you Brit members) as they had a longer threaded length versus Dirk's original Mercedes versions.

I don't want to re-install my subframe until I am fairly certain I haven't messed this up.

Peter

PeterPortugal · « **Reply #23 on:** February 10, 2020, 12:55:28 »

Dirk,

I found a picture from an old post showing the hardware removed from the car. As you can see this is a "shoulder bolt" but the threaded section looks less than 22mm you recorded. I would guess you could tighten this bolt fully without over compressing the rubber or interfering with the top bolt.

Regards

Peter

dirkbalter · « **Reply #24 on:** February 10, 2020, 19:02:33 »

Peter,
I think you are correct. The answer lies in the bolt. My flange bolt as well as the plate did not come from Mb. These came from SLS. Sorry if I wasn’t clear on that. The motor mount kit (MB) included the lower donuts and some other hardware. Looking at the picture (as you already stated) an original bolt looks to have less thread. That would explain our problem.

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Author Topic: Motor mounts again (Read 4636 times)