Alfa Romeo 8C 2300 engine model

[MODEL A MODEL]

I have also wondered about what's inside the hollow arms, and what may be hidden there?

From a few images you can see the end of a bolt with a nut on it?



Since the starter contacts the starter ring there, perhaps there is a casting that helps to assure alignment and proper contact?

As I had been hoping to cast all this, (originally), I was hoping to figure out this mystery. It would require a special core to be captured by the larger mold, and then to be destroyed in the clean out? -or possibly this area could still be machined from the "sump" area when flipped over and worked upside down?

[stompin]

Hi Don,

I think I know what that bolt is for. The rear bearing cap is a large block that is part of the crank case and it goes right to the oil pan gasket so 100mm. With the 2 bolts that hold it down like the other caps, that bolt goes right through case - cap - case to keep the cap from twisting. I have the model all apart right now but will get some pictures of it showing what I mean.

In that picture you posted, the bottom opening in the arm, is cupped on the outside. While the hole shapes changes from engine to engine, that cupping is always there. With the slope of the arm, a rod or bar put in it would require a widening hole like it has and the cupping would prevent the case from getting marred. I think that in period, that is how the case was carried around or even whole engines. I think that beside your mystery bolt is going to be a nook to keep the bar from shifting, but if it was deep enough the nook might not have been needed. However, I also think that the returns for the oil from the head on that end route through the back side of the casting next to the bearing cap. in The picture here they are the two holes on either side of the cap near the bottom of the engine. You can see the 2 drain returns for the front half right in front of the front bearing. How those rear holes were drilled is advanced level frustration that I am pretending does not exist for the time being for sanity.

I am still blown away that these questions exist, 90 years later, and am both dismayed and driven by it. attached are 2 pictures of a Jim Stokes crank case and a diagram that shows the oil returns.Attachment 36026Attachment 36027Attachment 36028

[stompin]

[stompin]

I think this is your bolt Gr. 66.

The starter is inline with crank, so that bolt is very low for it and is further forward then the flywheel. I think the starter is only held by 2 bolts. 1 that pinches the case, and one that keeps it upright. Both are on the front side of the arm. When I look at a starter by itself I see no way it could be mounted. The Jim stokes cases do not seem to have the bore for the starter going all the way to the rear, and look like it is walled off from the rest of the arm cavity, where the originals seem to have a round casting right to the back. But that is just based of those pictures alone as they are the only shots I have of it.

[stompin]

one more picture that shows the casting for the starter and one with the same bolt on the other side.

[MODEL A MODEL]

[stompin]

Here is a shot showing what I think that bolt is for. There are more pictures of it at the google photos link. The placement is not correct, I think I have it lower then it should be, or the flange below is thinker then it should be. It is within a few mm, but I still have a bunch of unknowns to figure out around it first.

That bearing cap has lots going on with it also. In the Jim Stokes case that I posted above, the cap is flush to the rear, and is a few mm thinner then the case walls on each side. The pictures from the classic car magazine spread that you posted have it almost flush to the inside. The sump pan bolts to it, it has t the long bolts for the bearing, the bolt that goes through it from the side. It has a recces for what I think is an oil slinger. What I think are 2 drains for oil that are drilled on an angle. It has more then one oil channel in the bearing, is a thrust bearing I think, and the has so many curves it should be censored. It think it is the most complex piece in the whole engine to figure out along with the cush drive and oil that is going on in the centre gears on the crank.

I said that the starter only has the 2 bolts, but am starting to doubt that, and think there might be one near the rear. I guess there could be a lip that helps keep it from backing out when pinched by the front, but it does seem like I am missing something. The starter is the same as the one from the earlier 6c 1750, but I am yet to try and find out more on it.

I also posted a picture of each arm cut away showing the large cavity on each side. You can see that I do not have an inside wall on the arms. Would those have just been solid or hollowed out leaving just what in needed for strength? Weight does seem like an afterthought with the 2300 vs 2900 so maybe its solid for that extra road holding weight.

[MODEL A MODEL]

Wow! Tom, You really are immersed in this project!

What that inside wall looks like is a mystery! Looking from the outside, where the Steering box supports are, the Engine mount / Wing, blends into the crank-case seamlessly. That area is hollow, probably maintaining a relatively constant wall thickness. I have always assumed that the inside wall is continuous, preserving a closed environment. Disturbed only by the bolt that you have pointed out? Your logic is unassailable, the bolt probably adds to the rigidity of the casting , that might be prone to flexing, metal fatigue and failure at just exactly the wrong place!

An aside? How are you doing? I hope all is as well as can be expected. Locally, here in Southern California, our Covid cases are rising and we're re-closing in fits and starts, my job is closed till the new year, so I can maybe get some real work done!

In the mean time, Happy Holidays! take care! -and of course thank you for all that you share!

Don

[MODEL A MODEL]

Two new questions?

Firstly, on the upper surface of the Engine Mount Arms / Wings. On the Stokes and Pur-Sang recreations, there appears a hole? Probably to aide assembly? -but I don't think that, that hole is on any of the original castings?

Second question is about the ends of the engine mounts. The "Clover Leaf" recesses? Originally I thought that theses areas were just that, recesses. But I have grown to think that they might be through holes? In some of the higher definition images, they do seem to show the interior of the arms?

This would all be so simple if one of us had access to an actual engine!

[stompin]

Thanks Don,

Immersed is a nice way to put it, sounds so much more pleasant than what I assume the clinical diagnosis would be.

I figure the cross bolt helps because the bolts for that one cap are 100mm vs 65mm for all the others. Add in that it is an outside wall, (the front bearing is internal), is very wide with a 40mm bearing but the cap is 56mm with the oil slinger recces where the other bearings are only 24 and 28mm. Add the twist of a straight 8, the torsional load would make curves out of straight lines. The more I look at it the more I think the Jim Stokes versions are different in that area. Their flywheel and clutch are significantly different, the inside shape of that rear cap looks about half as deep, and I have not found a picture of the original cap from the outside.

Attached is a Jim Stokes flywheel. Compared to the original that i posted up above and there is no clutch basket like the originals, so the clearance behind it is different without the springs. The other picture is looking at someone showing the rear bearing a good time.

Glad you are keeping safe and have some time to get down to business. I have been lucky and have been able to disregard work at a much higher efficiency at home for the last year. I am in Toronto, and while our numbers are high for the country, they were keeping fairly steady until recently. Our daily numbers have gone from 100/day in early september to 800/day now, so not looking like it is going to let up soon.

I am happy to share any bit I can. It helps to explain it as a single thought to work out the problems.. As you well know, I have changed my mind about every little detail on this and could argue for any measurement . I took some time and looked through old saved files a few weeks ago, and it could stand in for the case file to have me committed. I don't think I will ever get it all correct, but I would like to get the details in it. It is an interesting engine, and its a shame that it is a mystery to most. I have no real plans for it when its done, but will share it with anyone that has an interest in it, even if they are crazy enough to make one at 1:4.

[stompin]

I have found one of the holes on the intake side only on an original not on them all. there could be one on the starter side, but I do not have as many pictures of that side. Each case it seems is different. A few were steel, some were magnesium, most were aluminum. Some have a coarse finish, some have a smoother finish, some (the magnesium ones I think) almost have a brushed finish. Some of the mounts for the steering box are hollow, some are not, some have one hollow and the other not. some have a cupping to the steering box, some don't.

Some of the "clover leafs" sure look open, but I have flirted with the idea that the top of the cloverleaf is only open to the bottom not the whole arm. Its not the entire area of the section either, but the centre of each leaf. About those ends, I think each engine is a different thickness at the mounting face. I keep seeing these plates between the arm and the frame. and they have a number stamped on it with a matching number stamped on the arm at the same spot. so a 3,3 or 6,6. As if they shrunk after cooling from the casting , and had a plate made to fill in each side. I will put some pictures in the google photos link showing some variations.

[stompin]

They are in there now at the bottom. Each one of those is an original I am fairly sure. And each one has a visible difference. The mounts for the steering box also have a hollow on the back on the brush surface one. one has a hole etc. If you look at them all for to long you might start to hear static.

[MODEL A MODEL]

Steel? Really? That would make a very heavy engine. Maybe just the cylinder block?

And Magnesium, makes sense, it's light, casts easily, a common alternative to Aluminum.

I have noticed the shim plates, and there could very well have been shrinkage, I'm sure there was/is.

The "Clover-leaf" sometimes appear as partially webbed, I'm imagining a bit of flash left over from a mold not quite locked in place. I assume these were sand cast, but they may have been investment or some ceramic shell? In any case a core must have been used in those wings, to create the hollows, and those cores had to be supported by core prints along the outside edges of all those open areas.

I have tried to imagine how all of this was done, and do hear static, but thought that it was Tinnitus!

1:4 scale by the way is the only civil scale for a gentleman-modeler to work in. 1:8 is acceptable, 1:12th is pushing it, and the rest are barbarous! Don't ask me about 1:43rd!

EDIT, This last comment is said in jest, I can appreciate all scales, and have worked in most of them. (But 1:43rd is a weird scale)()

[Roger Zimmermann]

EDIT, This last comment is said in jest, I can appreciate all scales, and have worked in most of them. (But 1:43rd is a weird scale)()

1:43 is requiring less details, unless you have a microscope to work and a very sophisticated machine park to manufacture the tiny parts!

From the few comments I'm reading from this topic, most people like to know "how was it done" and "why this or that". I'm in a fortunate position to have hundreds of pictures giving an answer to most of my questions for my own project.