3.5 V8 Engine hitting steering box under load

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Fozza
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3.5 V8 Engine hitting steering box under load

Post by Fozza » Thu 18 Jul, 2019 5:01 pm

I've just had the subframe mounts on my 3.5 replaced. When I drove off, I heard a nasty grinding/knocking sound from the engine bay on initial acceleration. I took the car back to my mechanic and we did a little exploration. It turns out that when the engine is under load it torques to the right and is scraping against the steering box (newly rebuilt too!!). I've put new engine mounts in her, but there seems to be sufficient sag / drop to with the engine that allow this problem to occur. Ouch! Has anyone encountered this before? Could it be there are special engine mounts for a 3.5 (eg, have more lift) than a straight six (I'm pretty sure I had just 'W108 engine mounts' put in). Any other ideas from the wise?? I'm clueless!!
Thanks kindly in advance.
Fozza
1972 W108 280SE 3.5 (Betty)
1978 W123 230 (Under reconstruction)
1980 W123 300D (Simply Red - Gone to a young enthusiast)
1989 W126 300SEL (Zsa Zsa - daily driver)
1989 W126 300SE (The Yakuza Staff Car - gone to a good home)

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drew56cus
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Re: 3.5 V8 Engine hitting steering box under load

Post by drew56cus » Sat 20 Jul, 2019 9:14 am

This is common from what I can tell as there is bugger-all room there. As soon as anything gives a bit, there is contact. I did some selective filing to reduce the incidence of contact on my car (4.5 V8 into a finnie, which is essentially the same as 3.5 in 108). I am not aware of any different mounts. You may have to make some thin spacers to raise the engine mount up a bit, and flare out the mounting holes so the rubber is not being distorted (if it moves up, the gap between the mounts gets skinnier as they are angled inwards).
Drew
'65 220SE 4.5 Frankenbenz finnie :)
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Fozza
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Re: 3.5 V8 Engine hitting steering box under load

Post by Fozza » Sat 20 Jul, 2019 8:37 pm

Thanks Drew. Good tip on spacers. I'll also do some judicious filing of the bolt from the manifold that is the primary contact problem. I had a look at mounts on mbclassics and they have different mounts for a 3.5 than a 2.8 (even tho' the pics look the same!). I'll give them a crack too. Between the spacers, file, and new mounts a trust I'll find some joy!
4.5 in a finnie. -nice!
Fozza
1972 W108 280SE 3.5 (Betty)
1978 W123 230 (Under reconstruction)
1980 W123 300D (Simply Red - Gone to a young enthusiast)
1989 W126 300SEL (Zsa Zsa - daily driver)
1989 W126 300SE (The Yakuza Staff Car - gone to a good home)

Fozza
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Re: 3.5 V8 Engine hitting steering box under load

Post by Fozza » Thu 15 Aug, 2019 8:01 am

New engine mounts and engine stabiliser shocks have sorted the problem! I like it when it's simple! Judicious filing may be required but looking good so far!!
Fozza
1972 W108 280SE 3.5 (Betty)
1978 W123 230 (Under reconstruction)
1980 W123 300D (Simply Red - Gone to a young enthusiast)
1989 W126 300SEL (Zsa Zsa - daily driver)
1989 W126 300SE (The Yakuza Staff Car - gone to a good home)

CraigB
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Re: 3.5 V8 Engine hitting steering box under load

Post by CraigB » Thu 15 Aug, 2019 10:43 am

Thanks for reporting back Fozza, had wondered how it went. So do you think you had the wrong mounts? eg. 6cyl? Did they look thinner etc? Also what brands were they? Just trying to gather info so i avoid a similar situation!
Craig Baulderstone
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Re: 3.5 V8 Engine hitting steering box under load

Post by Fozza » Fri 16 Aug, 2019 7:40 am

They were Meyle Craig. Lord knows how long they'd been in there. They were thinner, but only as a result of being flattened over time! There was a significant difference in height to the new ones as a result. I did a little research, and the 3.5 mounts I bought via MB Classics are apparently harder but not higher compared to those for a straight six M130 motor. https://www.mbclassics.de/motor-mount-M116-M117
However the new 'unsquashed' height gave the engine the necessary lift.

That, in combination with new and functioning engine dampers did the trick. The old engine dampers were completely shot - the new ones really helped stabilise the twisting and torquing of the motor itself. There is still only a gap of a few millimetres between the bolt at the end of the manifold and the steering box, but it is sufficient. I could even do a small amount of 'judicious filing' to feel entirely comfortable, but the issue of the steering box being hit under load is resolved....happy days!
Fozza
1972 W108 280SE 3.5 (Betty)
1978 W123 230 (Under reconstruction)
1980 W123 300D (Simply Red - Gone to a young enthusiast)
1989 W126 300SEL (Zsa Zsa - daily driver)
1989 W126 300SE (The Yakuza Staff Car - gone to a good home)

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Re: 3.5 V8 Engine hitting steering box under load

Post by CraigB » Fri 16 Aug, 2019 10:52 am

What's your gearbox mount like too? If that is sitting low, I imagine that could affect clearance at the back of the motor.
Craig Baulderstone
280s's
280SE3.5
280SL Ruby
300TE Otto
350SL Gloria
350SLC Lurch
450SEL Boris
500SEC's...including Syd
560SEL's Foufou and Zac

Fozza
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Re: 3.5 V8 Engine hitting steering box under load

Post by Fozza » Fri 16 Aug, 2019 12:04 pm

Luckily i did that last month!! Good tip tho' - cheers..
Fozza
1972 W108 280SE 3.5 (Betty)
1978 W123 230 (Under reconstruction)
1980 W123 300D (Simply Red - Gone to a young enthusiast)
1989 W126 300SEL (Zsa Zsa - daily driver)
1989 W126 300SE (The Yakuza Staff Car - gone to a good home)

Fozza
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Re: 3.5 V8 Engine hitting steering box under load

Post by Fozza » Sat 17 Aug, 2019 6:51 pm

Having said that.....Craig, I'm displaying my ignorance here - but is the rear transmission mount (in the boot) different to the gearbox mount? I've replaced the former. If the gearbox mount is different I'll need to replace that too. Appreciate your greater wisdom on this!
Fozza
1972 W108 280SE 3.5 (Betty)
1978 W123 230 (Under reconstruction)
1980 W123 300D (Simply Red - Gone to a young enthusiast)
1989 W126 300SEL (Zsa Zsa - daily driver)
1989 W126 300SE (The Yakuza Staff Car - gone to a good home)

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Re: 3.5 V8 Engine hitting steering box under load

Post by John Green » Sat 17 Aug, 2019 8:15 pm

Fozza wrote:
Sat 17 Aug, 2019 6:51 pm
Having said that.....Craig, I'm displaying my ignorance here - but is the rear transmission mount (in the boot) different to the gearbox mount? I've replaced the former. If the gearbox mount is different I'll need to replace that too. Appreciate your greater wisdom on this!
Diff mount and transmission mount are very differant things. Not that surprising to have a lot of rubber parts fail at once. I explain 20 year old rubber components like this to our younger male customers. "would you use a 20 year old condom?"
M.B Spares & Service 14-16 Lyell St, Fyshwick ACT. Ph 02 6239 1099

http://mbspares.com.au - Supporting Australia's Mercedes-Benz Enthusiasts.

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Re: 3.5 V8 Engine hitting steering box under load

Post by CraigB » Sat 17 Aug, 2019 8:39 pm

Yep - your talking about what i would call the diff mount. Then engine and gearbox/transmission are bolted together as one 'rigid' unit which is attached to the body at 3 points - 2 are the engine mounts and the third is on the gearbox/ trans - so it can affect all those clearances. If you've gone that far, I would replace that too.

eg. from a quick google https://www.ebay.com.au/itm/1971-For-Me ... 0677.m4598
Craig Baulderstone
280s's
280SE3.5
280SL Ruby
300TE Otto
350SL Gloria
350SLC Lurch
450SEL Boris
500SEC's...including Syd
560SEL's Foufou and Zac

Fozza
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Re: 3.5 V8 Engine hitting steering box under load

Post by Fozza » Sun 18 Aug, 2019 7:08 am

Thanks Gents - that's much clearer now - much appreciated!
Good analogy John! Gets the message across nicely...
Fozza
1972 W108 280SE 3.5 (Betty)
1978 W123 230 (Under reconstruction)
1980 W123 300D (Simply Red - Gone to a young enthusiast)
1989 W126 300SEL (Zsa Zsa - daily driver)
1989 W126 300SE (The Yakuza Staff Car - gone to a good home)

Fozza
E Class
Posts: 61
Joined: Sun 15 Jan, 2017 11:53 pm
Model you own: I own multiple different models
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Location: Lismore

Re: 3.5 V8 Engine hitting steering box under load

Post by Fozza » Sun 18 Aug, 2019 7:10 am

....and thanks for the link Craig...
Fozza
1972 W108 280SE 3.5 (Betty)
1978 W123 230 (Under reconstruction)
1980 W123 300D (Simply Red - Gone to a young enthusiast)
1989 W126 300SEL (Zsa Zsa - daily driver)
1989 W126 300SE (The Yakuza Staff Car - gone to a good home)

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