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I am having a couple of problems on track with the BMW. The engine is shifting forward under hard braking causing a bolt on the front of the head to put a hairline crack in the cooling overflow tank. Also the transmission came out of gear twice on full course going around turn four the hard left hander.

The fix for both these problems is to replace the engine and transmission mounts with polyurethane ones.

Now the question. Section 14.10.G Engine mounts says "Any non=metallic inserts may be used". On the BMW (and I guess most other cars) the transmission mounts are also the rear engine mounts. So can I replace the rear engine mounts with urethane ones and still be STS legal?

One thing that would seem to say that I can't is that in the Street Prepared section the handbook lists the transmission mounts specifically in section 15.10.L

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Mitch Moore

I would say if it attaches to the engine and is referred to in the service manual as an engine mount, it's ok. If it's a transmission mount, you already know the answer.

Now if you had AWD, you could call the transmission mount a "front differential mount" & it would be legal.

my understanding is that poly is ok as long as your trading old rubber for new poly in the same amounts. so if an old bushing was rubber w/ a metal core you can use a new bushing that is poly w/ the same size metal core, but not a poly bushing w/ a bigger metal core.

so i guess the nonmetal to metal ratio in the bushing has to stay the same.

I don't think that this is true. If the oem part is rubber and metal then you can only replace it with rubber and metal.

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Mitch Moore

Sounds like people are trying to mix and match the rules for motor mounts and the rules for suspension bushings.


If you are unsure of the legality of a part, email the people that write the rules and ask for a clarification:

seb@scca.org

Scott

I don't understand the distinction you are making.

Section 13 Stock category Paragraph four " Alternate components which are normally expendable and considered replacement parts(eg. ....suspension bushings,drivetrain mounts, etc.) may be used provided they are essentially identical to the standard parts (e.g. have the same type, size, hardness, weight, material etc.), are used in the same location, and provide no performance benefit."

There is definately a difference in hardness between rubber and polyurethane and a performance benefit.

I will sent a email to the SCCA just to make sure what is allowed.

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Mitch Moore

Mitch-

I thought Dan was paraphrasing rules for suspension bushings (14.8.B) "metal to nonmetal content can not be changed"...

As for you citing section 13 "Stock Category," I'd suggest looking in section [b]14[/] Street Touring category.

14.3.G deals with the motor mounts, and the wording is similar to the suspension bushings.

As long as the transmission mount is actually considered a motor mount (and I think it is), you ought to be good to go (many parts catalogs will refer to the transmission mount as a "rear" motor mount).

Scott

I understand now that Dan was writing about STS and not Stock class. Thanks for setting me straight.

Thanks for suggesting sending an email to the SCCA. I had a responded from Doug Gill in thirty minutes with the following good news.

Hi, Mitch,

If you check the November FasTrack (from the link in my signature), you’ll see that non-metallic (i.e., polyurethane) transmission mounts are being added to the Street Touring allowances for 2006. You can also use non-metallic differential mounts.

Hope this helps.

Doug Gill

SCCA Solo Technical Manager
P O Box 19400
Topeka, KS 66619-0400
1-800-770-2055

SCCA National Solo Rules - http://www.scca.com/Solo/Index.asp?IdS= ... 050|070&~=

FasTrack - http://www.scca.com/Garage/

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Mitch Moore

Hmm, that was easier than I thought it would be.

Looks like you have a new project Better hurry, it's just a few weeks till Rockingham!

Scott

I guess I'm curious here as well. I was going to install an X brace on the 328, but don't know if it's legal in STS. Anyone know? Seems it would be since you can install a strut brace and camber plates.

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Rodney

'08 Bullitt mustang, CAM 7
Autox VP '09-'10, President '11-'12, interim President 2nd half of ‘14
proud recipient of the Bowie Grey service award '12
Now just a guy driving a mustang....

Picture?

Nope. That would be allowed in *SP when you can have other cars on the line that can swap items (is this from the convertible?) But X braces aren't allowed in ST* IIRC.

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Has no responsibility whatsoever.