Finishing Samson the M120 R107 - Page 13 - PeachParts Mercedes-Benz Forum

vwnate1 · #**181** 01-23-2021, 06:35 PM

You sir, are a fine Craftsman and I wish my skillset was anywhere near yours .

Roncallo · #**182** 01-27-2021, 06:40 PM

The rush is now on. I have to get my house up on the market by April 1. That means I need to complete the subframe by mid April. I just ordered the top plate and it should be in by mid February. I think I can do it. I really want to move to CT with a completed vehicle without having to remove the subframe and then reinstall just to move the vehicle. This plate is being made in the USA by Xometry as shipping from China was too expensive. I will see how they work out. They say free shipping?

I still need to get my subframe adapter mounts made, but I cant complete the design until my urethane bushings and my stock 107 bushings come in.

Roncallo · #**183** 01-31-2021, 12:58 AM

Yesterday the new stock subframe mounts came in. With those I was able to install them and estimate the deflection under load. It turns out the front mounts deflect ~ 4.47mm and the rear mounts deflect ~7.27mm with the body weight placed on them. I needed to know that to figure out the height to mount my urethane bushings at since the urethane bushings don't deflect nearly that. Unfortunately my urethane mounts did not come in and I will need those measured as well, Hopefully they will be in Monday. I also decided to make the bushing mounts myself since I found a perfect piece of material to make them. I got the metal turned down to a rough size today but I will need to measure up the real ones to get to the final dimension.

The first picture shows the subframe bushing installed with a bolt going through it to squeeze to the desired load. The second picture shows the bolt and socket I had to use to allow the bushing room to move under compression. The third picture shows the subframe bushing mounts being made.

Deflection can be figured out by the number of turns of the nut times it's thread pitch.

Load on the bolt assembly can be estimated using the formula T = k*D*F. Where T = bolt torque. k is a coefficient, generally us 0.2 for dry bolts or 0.15 for lubricated bolts. D = the major diameter of the bolt and F = Force.

In this case we want the load so the equation can be rearranged to F = T/(k*D) or you can just cheat and plug in all the numbers at this websight.

https://www.engineersedge.com/calculators/torque_calc.htm

So using a torque wrench with a tell tale needle, I tightened the bolt 6 turns and read the torque at each turn. Then from the torque at each turn I can plot the load on the subframe mount.

The only problem is that I need the load on each subframe mount. That is estimated using a SWAG (Scientific Wild Ass Guess). The load on the subframe is ASSUMED to be: The total weight of the car - engine and all accessories bolted to it and 1/2 of the transmission. Now assume the car without the engine and trans has a 50/50 weight distribution, so half of that weight is on the front wheels. The weight of the front tires and wheels as well as the front subframe itself and suspension also needs to be deducted. I did weight most of these items at one time or another and estimated others. With all that done you now has the weight on all 4 front subframe mounts, half of which is on each side. Now all that is left is to find how much weight is on the front bushing and how much is on the back. It turns out that the front axel spindles are about 2/3rd the distance between the front and rear subframe mounts towards the back. Therefor the rear mount caries 2/3rds of the load and the front caries 1/3rd. I actually measured more like 67/33% using crude measurements. After throwing all those numbers is an turning the crank, I got 221Lb on the front mounts and 377Lb on the rear. A lot of guesses and assumptions but I will bet a beer I'm within 50 Lb. But the target is huge, those sub frame bushings deflect a huge amount in operation. My stiff urethane mounts need only to be placed within that huge range.

Roncallo · #**184** 01-31-2021, 08:52 PM

I got the temporary engine mount plates in place today. Not sure If I'm ready to tack weld in place yet. I was also able to define where to cut out for the left engine mount. The left engine mount has a part the drops below the plate and interferes with the forward edge of the rear cross member. With the tooling in place I was able to define where to remove the forward edge. This time I was able to keep above the seam of the subframe. I'm hoping all of the top plate with be able to remain above the seam. I will have to see when the plate comes in.

Roncallo · #**185** 01-31-2021, 11:43 PM

And now the front subframe mounts are cut off.

Roncallo · #**186** 02-01-2021, 01:34 AM

It turns out that everything I told you in post 183 is a total crock. I forgot 1 thing, and that is that the subframe mounts are preloaded to a load greater than the weight of the car. So what I posted in 183 is true for worn out subframe bushings where you can see the washer hanging low and can spin the rubber bumper. But for good mounts the bolt pulls the subframe bushings beyond the weight of the car. I retested the deflection of the mounts with a new subframe bushing and just measured the difference in deflection between finger tight and fully torqued. Its about 4.74mm.

Roncallo · #**187** 02-02-2021, 01:22 AM

My urethane bushings came in today along with my side plates. With the urethane bushings in hand I was able to analyze them for compressed installed height and set the final mounting height. With that I was going to machine out the final depth of the bushing mounting pads but I ran into another problem. And that is when I machine them out the upper portion of the subframe will be broken and unconstrained. Since they hold the upper control arm mounts I cant afford to allow them to move out of position. So that means welding in the side plates prior to machining. That also means taking it out of the fixture which is a no no in machining. In addition I need to build a welding fixture before I weld to hold the subframe constrained and not allow it to warp during welding. So I do have a plane where I can machine 3/4s of the area and still tach weld in plates for evaluation prior to removal from the machining fixture. I will probably work that out tomorrow. Note the laser cut side plates that need to be ground down and hand fitted into the cavities. below the upper control arm mounts.

Picture 1 shows the urethane subframe bushings.
Picture 2 shows where the subframe area that needs to be machined down to the seam, leaving the area unconstrained.

imgolden · #**188** 02-02-2021, 01:07 PM

You're a pilot I take it? Your IMC comment is what makes me think so.
These cars seem to attract a lot of folks in aviation, including myself.

Roncallo · #**189** 02-02-2021, 05:57 PM

Quote:

Originally Posted by imgolden

You're a pilot I take it? Your IMC comment is what makes me think so.
These cars seem to attract a lot of folks in aviation, including myself.

Yes I'm a pilot, fixed wing and rotor craft. But I haven't flown in about 10 years.

vwnate1 · #**190** 02-02-2021, 09:25 PM

You're getting a priceless FREE lesson on advanced Hot Rodding here, a true American pastime, not just slapping any old big engine into some other chassis.

Roncallo · #**191** 02-03-2021, 07:55 AM

Top plate is complete and ready to ship form China. It will be in soon.

Roncallo · #**192** 02-04-2021, 12:59 AM

Got the front subframe pads milled down. I made temporary pads to tack weld in place to do a fit check. Once the fit check is complete, those will be laser cut.

Roncallo · #**193** 02-04-2021, 11:41 PM

Not a whole hell of a lot done today. Had too many chores to do. But I completed the temporary mount for the other side and got them both tack welded in place. I also visited a scrap yard and picked up some steel I beams to make a welding fixture and rough cut them to size. Tomorrow I have to take the wife out on a date so not much is going to get done.

Roncallo · #**194** 02-05-2021, 11:29 PM

One subframe mount is rough cut. Almost lost it in the transition, one little screw up, but being those are made of 100KSI steel and the stock MB subframe mounts are cast aluminum, I'm not too concerned. I will need to get the second one to that stage before I reset the lathe up to do the back side on both of them.

Roncallo · #**195** 02-06-2021, 11:18 PM

Subframe bushings are almost complete. When I get my milling machine back, they will need to have a flat milled one the side of that 2.5" diameter area for engine clearance.