help to understand the opening spring of the front hood

[deQuincey]

how to fix the opening torsion system of the front hood

hi

i have disassembled the front hood system of bar and springs (torsional), that aids the opening of the front hood

in the case of my car the system was not properly assembled, and that incudes the fixed point in the fender, in which the washers and bolts were wrong, and thus that point was COMPLETELY fixed !

i heard that this is not correct, because this point must freely displace forwards and backwards

i would appreciate some explanation of the function of the system in a good working case of yours, and detailed photos to recover my assembly to a good condition

remark: i have cleaned everything and now is in the paintshop, just when i learn how to assemble it i will do !

regards and thanks in advance !

 

[HB Chris]

The mounting bolt for the arms on the fender is fixed, it should not move back and forth if I understand your comment correctly.

 

[Sven]

Yes, the bolt should be fixed in the fore and aft direction. It should pivot freely on the special collared bolt. It is critical that the bolt be positioned correctly fore/aft. If it is positioned too far forward the elbow will press into the inner fender metal when the hood is closed - causing damage. Don't ask me how I know. I have the engine out of the car so it is easy to see what is happening by crouching inside the engine compartment while carefully closing the hood. I expect to me doing this work in about 2 months and can take a picture if that helps.

 

[jmackro]

deQuincey:

Some of your questions were addressed in a similar thread that began last summer:

http://www.e9coupe.com/forum/showthread.php?t=6945&highlight=hood+prop

As Sven wrote, the hardware that attaches the arms to the fender are "shoulder bolts" that can be tightened without preventing the arms from rotating.

 

[johanaxelson]

yeah, I will 3rd that. You need that special bolt. be careful or you will damage the paint.

BTW, I am one short. Anyone know a source?

 

[deQuincey]

The mounting bolt for the arms on the fender is fixed, it should not move back and forth if I understand your comment correctly.

right, that was part of my question, so the bolt is fixed ????

here you can see the bolts used in this point:

and here my two schemes:

the two assemblies are possible, the A case fixes the bolt to the arm of the spring-mechanism, but the bolt itself can rotate and displace along the square hole present in the fender support, so two degrees of freedom are possible

the B case fixes the bolt to the fender, and thus the arm can only rotate

which is the correct one ?

regards

 

[JhwShark]

IIRC, B is proper.
Jon

 

[jmackro]

A case fixes the bolt to the arm of the spring-mechanism, but the bolt itself can rotate and displace along the square hole present in the fender support, so two degrees of freedom are possible

deQuincey:

Nice drawing - I wish everyone was clear in posing questions and answers!

As JhwShark wrote, the correct answer is "B". I understand your question about "displace along the square hole present in the fender support". While there is an elongated hole in the support, the pivot for the arm should be securely clamped at some point along that hole. The hole is elongated to provide some adjustment for hood alignment, accident damage, tolerance build-up, etc - not because the pivot needs to slide fore-aft.

 

[deQuincey]

As JhwShark wrote, the correct answer is "B". I understand your question about "displace along the square hole present in the fender support". While there is an elongated hole in the support, the pivot for the arm should be securely clamped at some point along that hole. The hole is elongated to provide some adjustment for hood alignment, accident damage, tolerance build-up, etc - not because the pivot needs to slide fore-aft.

ok, i understand the function and i will adopt solution B, thank you all for the explanations

now i am continuing with the questions, i have read patiently the thread that you kindly linked to, and now i foresee more problems than expected

when i dissassemble the whole system, it was not really difficult to do so, i only found some tension, but it was ok trying to find a neutral position of the hood, and there i undo the long mentioned fender bolts

now i can hardly understand the pre-tensioning issue.

this is the chris macha text: "Put a blanket on the floor, place torsion rod on blanket, attach an 18" long strap of steel bar to the mounting points on one end of rod and use the two bolts to hold it in place, with steel strap on floor, pull arm towards strap until the L bracket can slip behind the arm and keep it tensioned, repeat on other side. It is pretty easy to do once you have the leverage."

i was not thinking of doing anythin of the kind, but now i feel puzzled

advise ?

 

[61porsche]

Alternate

http://www.seniorsix.org/faq/hood.html

 

[jmackro]

Oh, I understand your confusion.

You only need to do the procedure that HBChris described when installing a new hood tensioner. Or one that has has its two small "L" brackets removed. As long as your old tensioner is in good shape, and you have not taken off the "L" brackets, you can ignore that procedure involving the blanket and steel strap. By the "L" bracket, I mean the steel piece shown in the photo below that is attached with the two 6mm bolts:

 

[deQuincey]

thank you all, ...continue

yes you are right, now with your help and the help of others, i am understanding things

my problem was that my starting position was wrong, due to the fact that my spring-mechanism was badly assembled and thus not working at all, so all my ground assumptions were wrong !

now i am making a sort of a postdoc thesis !, :-D:-D:-D

this is what i understand of the way it works, please confirm or correct my ideas:

lately i added a #4# point: the stop of the hood opening due to interference between top arm and "L" shaped brackets (see attached pic):

if this is right, now my mind will work out a solution, let´s see:

the problem is that i think it will be very difficult to pre-tension the two internal spring-bars with everything out from the car, in a blanket, due to the fact that when you try to do so, the lateral internal supports (made of aluminium) will tend to go out from their position inside the bar ends (the torsion of the spring-bars will be supported by them, and you know they are only a little way inside the main bar)

so unless you limit the possibility of those lateral supports to go out from the bar (restriction of their lateral displacement), you will be in trouble while charging the torsion in the springs

but there is a place in which that displacement is naturally restricted, ...that is mounted on the car !,

in this condition i think i could do the following (i will use your interesting pictures to help me explain it)

my intention is to mount the whole mechanism in the car, without the L-brackets, or to tell you the truth, with the L-bracket swang out of the way of the top arm, fixed only with one of the M6 bolts (the one in the top)

in this situation i am assuming that the arms will be in the "1" position represented in the photo, painted in blue colour

then, i will force the arm towards the "2" position, and then put the L-bracket in its place and secure it with the green arrowed screw

then i will do the same in the other side

what do you think ? do you see any inconsistence in my solution?

i will appreciate your help !

 

[deQuincey]

amendment

to be able to do the previous procedure, the L-bracket has to be modified

the question is that is impossible to install the top M6 bolt and rotate the L-bracket, because the top part of the L-bracket will be interfering the way of the top-arm whilist i move it from position "1" to "2"

so a new L-bracket must be produced for this purpose

i will also increase the thickness to follow your advice of doubling it

 

[jmackro]

deQuincey:

I think you are saying that your hood torsion assembly IS apart - or you have bought a new one - and you DO have to do the procedure that HB Chris described.

the problem is that i think it will be very difficult to pre-tension the two internal spring-bars with everything out from the car, in a blanket, due to the fact that when you try to do so, the lateral internal supports (made of aluminium) will tend to go out from their position inside the bar ends (the torsion of the spring-bars will be supported by them, and you know they are only a little way inside the main bar) so unless you limit the possibility of those lateral supports to go out from the bar (restriction of their lateral displacement), you will be in trouble while charging the torsion in the springs

Yes, you are right. The aluminum pieces that retain the ends of the torsion bars can slip outward, releasing the bars. They usually don't, but they could.

my intention is to mount the whole mechanism in the car, without the L-brackets, or to tell you the truth, with the L-bracket swang out of the way of the top arm, fixed only with one of the M6 bolts (the one in the top)

in this situation i am assuming that the arms will be in the "1" position represented in the photo, painted in blue colour then, i will force the arm towards the "2" position, and then put the L-bracket in its place and secure it with the green arrowed screw

No, you can't do it that way. Without the "L" brackets securing it, the arm is NOT in the #1 position. It is well beyond what you have drawn as #1. In other words, you cannot bolt the torsion assembly to the hood until you have pre-tensioned the springs.

the question is that is impossible to install the top M6 bolt and rotate the L-bracket, because the top part of the L-bracket will be interfering the way of the top-arm whilist i move it from position "1" to "2"

No, you don't need to modify the "L" brackets like that. You can attach them loosely with one bolt, rotate them into place, and then install the second bolt. No slotting or cutting is necessary.

In fact, I found the "L" brackets to be too weak to withstand the force of a new torsion bar. I had to double them up - install two at each position (fortunately I had both my old ones + the new pair that came with my new assembly). Cutting the "L" brackets as you describe would leave them far too weak.

 

[Sven]

deQuiincey,

I have all the pieces laying on my desk. It looks that the arm would need to rotate another 45° or so beyond position 1 in your diagram to be in the relaxed state (ie, pointing out through the front of the hood).

 

[deQuincey]

probably you are right !

deQuincey:

I think you are saying that your hood torsion assembly IS apart - or you have bought a new one - and you DO have to do the procedure that HB Chris described.

yes my assembly IS apart, but it was not in tension when it was in the car, so taking it away from the car was not complicate !

Yes, you are right. The aluminum pieces that retain the ends of the torsion bars can slip outward, releasing the bars. They usually don't, but they could.

i remember that this was said by someone in the other post, so, yes, they could ! oh my god !


No, you can't do it that way. Without the "L" brackets securing it, the arm is NOT in the #1 position. It is well beyond what you have drawn as #1. In other words, you cannot bolt the torsion assembly to the hood until you have pre-tensioned the springs.

i can understand this, but then i question the state of my spring-bars, their ends (if you look in the direction of the long axis) are located at 90º, is this correct ? should they be 0º (this is one alligned with the other ?) maybe they are defective (or better they have overcome the plastic tension and they are deformed)

are they available at bmw nowadays ?

No, you don't need to modify the "L" brackets like that. You can attach them loosely with one bolt, rotate them into place, and then install the second bolt. No slotting or cutting is necessary.

In fact, I found the "L" brackets to be too weak to withstand the force of a new torsion bar. I had to double them up - install two at each position (fortunately I had both my old ones + the new pair that came with my new assembly). Cutting the "L" brackets as you describe would leave them far too weak.

thanks

 

[deQuincey]

deQuiincey,

I have all the pieces laying on my desk. It looks that the arm would need to rotate another 45° or so beyond position 1 in your diagram to be in the relaxed state (ie, pointing out through the front of the hood).

yes i was assuming that when i read the jmackro answer !

i will try to put the pieces like you, and post a picture tonight, and you might check it

i would appreciate if you can do so also !

regards

 

[jmackro]

i can understand this, but then i question the state of my spring-bars, their ends (if you look in the direction of the long axis) are located at 90º, is this correct ? should they be 0º (this is one alligned with the other ?) maybe they are defective (or better they have overcome the plastic tension and they are deformed)

Sorry, I don't have a torsion arm assembly apart so that I can answer your question. The torsion springs do wear out over time.

are they available at bmw nowadays ?

Yes, Mesa Performance here in the States was able to order replacement torsion springs, as well as the complete spring-tube-arm assembly from BMW. The price of two torsion springs was not that much less than the price of a complete new assembly. Because the welds between the arms and the tube tends to crack, Mesa recommended buying the complete assembly.

 

[HB Chris]

The entire assembly is around $130 last time I checked. There is no way to tension the spring bar in the car, the arms will interfere with hood or body and you have no leverage. Doing it on the floor took 2 minutes at most. The leverage was provided by attaching the steel bar so it rested on the floor and kept the assembly from rotating. The ends never looked like they were going to slip out. Hope this helps.

 

[Sven]

deQuincey,

Here are a couple of photos. The torsion bars are new (~$20 each). The close-up photo shows the right spring mount. For reference, the wood floor is the underside plane of the hood.