m117 4.5 block measurement - PeachParts Mercedes-Benz Forum

Tony H · #1 08-25-2011, 07:03 PM

Does anyone have a M117 4.5 without the heads on it. I have read that when the engine is at TDC the pistons are a small, certain amount below the deck. Wondering if someone can give me a measurement in MM how far the piston is down the bore at TDC.
Thanks
Tony

Benz Dr. · #2 08-25-2011, 09:43 PM

I believe you are right about that. I'm going to guess and say maybe 15 to 20mm below deck height. If I recall correctly the heads have no cumbustion chambers or very small ones.
What are you doing with the engine?

Tomguy · #3 08-25-2011, 09:55 PM

TDC.

GGR · #4 08-25-2011, 10:27 PM

Are these pistons flat? Later engines have a cavity in the center of the pistons for 8:1 and 9:1 CR and flat top for 10:1CR. But they all go up to the top of the cylinder to ensure a proper squish area. The 4.5 may have been developed before the importance of the squish area was taken into account. So, by shaving the block, one can go from 8:1 to 10:1 for quite cheap. Some cavities in the top o the pistons may be necessary to clear the valves. And the camshats may end-up quire offset. Not sure the most ofset key would be able to compensate. Intake maniold may also have to be shaved to compensate for slightly closer heads.

Tony H · #5 08-26-2011, 11:21 AM

Thanks for all your input.
I was quite happy with my 3.5's performance but it needs some work (heads rebuilt)so I starting thinking it would be a chance to upgrade a bit but still keep with the original theme. I was considering a 5.6 but it seems like too much trouble with my man trans and it is too much of a departure from original and I don't really care about the extra weight of the iron block. So I started thinking maybe I could do something like Tom did with the 4.5 w/ 3.5 heads. Then I drifted off and started thinking about boring it to 96.5 and turning it into a 5.0. At that point I'm sure the 4.5 heads would need to be used as the CR would be WAY to high with the 3.5 heads.
Has anyone ever bored a 4.5 to 5.0? That would reduce the cylinder wall thickness by 2.25mm. Not sure if is even worth the effort. I guess the 3.5 heads on the 4.5 is the biggest bang for the buck since I already have the heads with Euro cams and the Pick and Pulls have plenty of 4.5's in them. New rings and bearings and the 4.5 bottom end would be ready to go.

1960mog · #6 08-26-2011, 07:51 PM

Hi
The piston in the picture is a 8:1 CR used til 8/75.
If you bore the 450 block to 96.5, what pistons do you use?
500/560 pistons are iron coated to run in aluminum cylinders.
I don't know what a cast iron cylinder walls will do to this pistons.
There is also the question about ring material/coating.

Tony H · #7 08-26-2011, 11:29 PM

I don't know much about the alum engines. I guess the pistons are why no one has done it.
Thanks for the info.

GGR · #8 08-27-2011, 08:55 PM

Honestly, it would be less work, time and money to adapt your trans to a good 5.6 than modify and rebuild a 4.5.

I knew about the specific rings for alusil but I didn't know pistons were also special. What about fitting a 560 crankshaft? I know the rods are the same length. Pistons will go higher by 5mm. you should see if there is enough material on them to shave them so as to have a 10.1 CR.

Adapting a 560 crankshaft may require boring the crankshaft line in the block, I thing bearings are a bit bigger.

1960mog · #9 08-29-2011, 11:16 AM

Interesting idea.
The 560 crank will fit in the 450 bearings.
However, I don't know that the 560 crank will turn freely in the 450 crank web.
Another problem are the pistons. Even the flat tops shown in the picture above will perturb about 2 mm over the parting surface of the block and have no valve pockets.
450 pistons used from 75 to 79 are 4 mm higher then the flat tops, but they have a 9 mm recess in the center.
This pistons could theoretically be machined to fit the application.
The engine would have 92 mm bore and 94.8 mm stroke.
This pencils out to about 5030 cc.
Compression is yet to be determent.

Tony H · #10 08-29-2011, 11:26 PM

Yes the main bearings are the same however the 5.6 rod bearings are 4mm smaller(that's where they got the extra 10mm stroke) so one would need to use the 5.6 rods assuming they were the same length. I can't find any info on 5.6 rods. Anyone have a service manual? 4.5 rods are 154mm and 3.5 rods are 138mm. The CR could be determined by the volume of the combustion chamber+ whatever was left of the piston depression after machine. On a 3.5 the piston is actually above the deck by a small amount.
(.75mm)
Looking at my service manual there are different 6 pistons for 116's ranging from 7.5 to 9.5 cr and 13 different 117 pistons ranging from 7.5 to 8.7 cr. Of course most of these would be impossible to obtain.

1960mog · #11 08-29-2011, 11:34 PM

450 and 560 rods are the same length.

Tony H · #12 08-29-2011, 11:47 PM

Cool-my idea is gaining traction. I'm sure with the larger displacement the cr would be higher using the original 4.5 heads. Not sure what the volume of a 4.5 combustion chamber is but I'm sure by time the motor is stroked the CR will be pretty high. I would like to end up around 9.5.

1960mog · #13 08-30-2011, 12:30 AM

You probably get more then 9.5.
Those pistons have a CR of 8.0.
You have to cut them at least 6mm down.
The recess in the piston will then be about 3mm deep.
Now you compress a larger displacement in to a smaller chamber.

Tony H · #14 08-31-2011, 09:40 PM

I found a 78 450SL at the pick n pull with the heads gone. I want D-jet heads antway and it saved me the work of pulling the heads to inspect the cylinders. Cross hatching present and no lip at top of cylinder. Is this typical?
This engine has the dished pistons which are necesarry so there is material to remove on the top. Even after machining off some of the lip for the longer stroke there will be a substantion depression left.

GGR · #15 08-31-2011, 10:03 PM

The cylinders do not wear much on these engines. That said you should have them checked for ovalization, especially if you change the stroke.

These pistons have a squish area and the CR is determined by the size of the recess in the center. 10:1 pistons have no recess in the center, just some small recesses to clear the valves. If you shave the pistons you have to make sure the squish area remains the same, so measure the position of the top of the pistons and try to get them to the same place once shaved with the longer stroke.

The 3.5 heads have a smaller combustion chamber. Not sure this is what you want. You determine the CR with the pistons. I would try to source some late 5.0 or some 5.6 heads, they have bigger valves. I don't know if they will bolt on the 4.5 block. I think they will. But the chain tensioner is different, not sure about the way to go with that.

Djet and Kjet injectors are interchangeable. Not sure D-jet heads are specific. I did fit D-jet injectors and Megasquirt on a 5.0 euro that had Kjet originally. I think they sit a bit lower in the head, but they fit.

You should get some AMG replica camshafts from 48hp. The 3.5 won't do a good job. Lift and duration are dependent on the displacement. So a 3.5 is less "aggressive" than a 4.5 for ex.