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Simplex Connecting Rod Rebuilding and New Camshaft Bearings

connecting rod 1

This is Part VI of a series we are sharing with you showing some of the more interesting details involved in rebuilding a 100-year-old 1914 Simplex 50 h.p. Speedcar for the Collier Collection. This episode covers connecting rod rebuilding operations, and machining new connecting rod and camshaft bearings.

  • The lead image shows one of the 17-inch long connecting rods in a shop built connecting rod boring fixture. Just above it is an adjustable boring head, boring bar and cutter in the milling machine spindle. The boring head spins and is fed downward while machining the big end bore.

Just as the main bearings that were covered here earlier, the rod caps and bearing inserts had been filed numerous times to take up on wear to the babbitt-lined bronze-backed rod bearings. This was an effort to keep the bearings tight in the connecting rod bore and caps; in addition shims were inserted behind the bearings. Patch jobs like this generally only last a short time, and all of the bearings were quite lose in each rod when taken apart.

New connecting rod bearing inserts were needed, and the first step before making them is to rebore the lower ends of the rods round again for the precision fit that is needed; the job can be done on the shop’s special LeBlond connecting boring machine. Instead, it was accomplished using an adjustable connecting fixture fabricated in-house some time ago, set up in a vertical milling machine. This method will work better in this instance because the mill’s digital readout is very useful to deal with the varying center-to-center distances found in this set of rods.

Simplex Rod on Sunnen Hone

  • After boring, the connecting rod lower ends are given a smooth honed finish with a Sunnen honing machine. This provides for more complete contact between the bearing insert and the rod that helps in transferring heat out of the bearing.

While being powerful, durable, and state of the art in the 1908-1912 period, Simplex engine castings, and components were machined the old-fashioned way and many times the parts are not interchangeable. Bolt holes and stud locations vary in a single engine, and no two are exactly alike.

The center-to-center distance of this set of rods varied as much as .030 of an inch (30-thousands), and the four rod cap bolt holes are also are not in any standardized location. The caps had been filed as much as .008 in the past, and the lower end bores were oval.

One other consideration that needed to be dealt with was the connecting rod cap bolts. The location of the bolt holes vary considerably, and some of them and the bolt are open right at the edge of the bore. The use of sacrificial bolts instead of the originals while boring and honing allowed the originals to remain full size; later the bolts that protrude into the new bore are accommodated by relieving the o.d. on the new bearing inserts.

Simplex Connecting Rod and Cam Bearings

  • The four new replacement connecting rod bearing inserts are seen in this photo on the far-left and right; in between are partially machined cam bearings. All are made out of cored bearing bronze of the type in the middle top of the image.

The next part of the job is to machine the new connecting rod bearing inserts out of cored bronze stock in a lathe, and then cut them at the parting line in the milling machine. We have already shared with you in the past the replacement main bearings for this engine, and as the rod bearings are quite similar, refer to the link to learn how they are made. The only difference in the two types is how the babbitt is bored, and you can learn here how the connecting rod bearings are finished off.

Cam Bearing Manufacture 2

  • Cutting a cam bearing in half with a slitting saw in the milling machine. This operation is followed by milling the parting faces to a smoother finish than a saw cut provides. 

After the new camshaft bearings have been partially machined round and the holes for the fasteners that hold the halves together have been drilled and tapped, the bearing is cut in two on the milling machine with a slitting saw. This is followed by further operations that include boring the inside diameter of the bearing close to final size in the lathe, and then honing that bore to the finished inside diameter on a Sunnen honing machine.

Machining Camshaft Bearings 3

  • Setting up to finish machine the outside of a cam bearing in the lathe on an expanding mandrel.

Next each bearing is set up on a precision expanding mandrel in the lathe on the previously finished bearing bore. A dial indicator is then used to check that the o.d. of the bearing is running true to the i.d. Next the outside diameter is finish machined to a size this is only .0002 of an inch (two ten thousands) larger than the bearing housing in the crankcase. This fit will keep the replacement bearing from ever becoming loose again.

Simplex 50 HP Cam Bearings

  • The finished cam bearings and a shop made tool used to adjust the position of the bearings if needed after being installed in the crankcase. The pockets on either side of the top of the bearings are for collecting oil to lubricate the bearing and camshaft.

Just like every other early engine with an aluminum crankcase and high mileage that has been rebuilt here in the past, the original Simplex cam bearings were worn and also loose in the housing that holds them in the crankcase. In use, the aluminum crankcase has a higher coefficient of expansion when at operating temperatures than the bronze cam bearings, and in time looseness sets in and becomes an issue.

The fix is to line bore the bearing housings in the crankcase and machine new oversized diameter cam bearings with a slightly tighter fit in the bore than originally used. Many times the fit that should be a force or press fit (needs some force to drive it into position) was not tight enough to help ease the assembly process.

Quite often with a bit of planning and the construction of a simple tool, the correct fit can be used. The device if needed, is used after insertion of the camshaft and the bearings to orientate the bearing in the correct position so the anchor bolts that prevent bearing rotation can be inserted.

You can look back on all of the previous parts of this series here.

21 responses to “Simplex Connecting Rod Rebuilding and New Camshaft Bearings

  1. Would the variation in center to center distance between the pin and crank bores of these rods, also have been a function of how much the rod caps had been filed to reduce bearing clearances?

    Your explanation of the procedures followed to clean up the pin and crank bores is perfectly understandable. Was there any possibility that this remachining might have been helpful in reducing the center to center variation? I would think this variation would (a) make balancing the crankshaft that much more difficult and (b) would have produced inherent vibration in the engine that would have been difficult to overcome.

    Did you give any consideration to spray welding the cap/rod joint faces to build them back up? This would have helped decrease the amount of metal in the crankbore that needed to be removed to make the bore round again, and might also have been another way to reduce the center to center variation.

    What was the surface finish of the final honed crank bores? I’m guessing something in the range of 10-15 micro-inches?

    • Kevin, All good points that you brought up and they are answered below you questions.

      Would the variation in center to center distance between the pin and crank bores of these rods, also have been a function of how much the rod caps had been filed to reduce bearing clearances?

      No, The center-to-center distance was checked using the top half of the rod bore that had not been changed since new.

      Your explanation of the procedures followed to clean up the pin and crank bores is perfectly understandable. Was there any possibility that this re-machining might have been helpful in reducing the center to center variation?

      Yes, it was corrected by the rod re-bore and during the final machining of the babbitt.

      I would think this variation would (a) make balancing the crankshaft that much more difficult and (b) would have produced inherent vibration in the engine that would have been difficult to overcome.

      A: No, the crankshaft of an inline four is balanced by itself without out taking the rod weights into effect.

      B: No, the engine ran quite smoothly before rebuilding as it was precision-balanced in the early-1950s when it was last overhauled. All of the rod weights (1. lower end that is considered rotating weight 2. top end and 3. total weight were within acceptable tolerances) and still are after the changes.

      Did you give any consideration to spray welding the cap/rod joint faces to build them back up? This would have helped decrease the amount of metal in the crank bore that needed to be removed to make the bore round again, and might also have been another way to reduce the center to center variation.

      No, Because so little metal had to be removed (most of the correction was in the babbitt) it would not really affect the rods strength at all. The joint also has a complicated tongue and groove arrangement that would not lend itself to the process; also the heat involved would likely warp the rod caps even more than they all ready were and cause other issues to deal with.

      What was the surface finish of the final honed crank bores? I’m guessing something in the range of 10-15 micro-inches?

      It was not checked, but it is a known fact that the Sunnen 320 grit stones w/honing oil that were used give a surface finish of 10-20 RMS. The original finish was somewhat rough as it was an as bored finish. The new finish is probably 10-times smoother than the original.

      • My question regarding the spray welding was because I’d recently been to a seminar put on by Heller on their new process for spray welding the cylinder bores of an all aluminum cylinder block. Their process uses nitrogen as both the propellant for the molten material as well as a means to control oxidation. Also their process only requires heating the block to 180°C, which is both well below the melting point of aluminum and also well above the operating temperature of a modern engine. It ensured that there would be no cracking. The plasma based spray welding process requires pre-heating the part to a much higher temperature. I also recall seeing undersize crankshaft oil seal flanges spray welded to bring them up to a usable diameter without any kind of pre-treatment.

        I didn’t appreciate that there was a tongue & groove locating method between the cap and rod, so I understand now that spray welding would not have been suitable. The t&g would certainly have eliminated fore/aft movement of the cap relative to the rod.

        Between the honed surface of the rod crankbore and the much more precise bearings you are making, this rebuild will likely last tens of thousands of miles.

  2. Hi,
    Is it worth heating the aluminum crankcase to 300degF to install the cam bearings? You could get about .002″ interference if the crankcase /motor runs at 180deg, if you machine your cam bearings to .005″ oversize at room temp. Assuming 2 .130″ diameter cam bearings, they should slip into the crankcase at 300deg without force, even with 2 1/8 crankcase cam bearing bores. Or maybe the cam bearing set screw retaining devices are sufficient? Or maybe the crankcase would cool too fast to install the bearings before they seize up in the holes?

    • Lee, All good thoughts and I have done similar things for putting valve guides in aluminum heads and in some other similar situations.

      The reason I went with a .0002″ interference fit is because all Simplex aluminum castings are very prone toward cracking. A tighter fit could very well crack the cases while cooling down or when in use.

      I feel it will be enough to do the job and the cam bearings, even through made of bronze run at warmer than the crankcase and will also expand when up to temperature.

      One other issue is the way the cam and bearing are put in. First the #2 bearing is put on the shaft, the cam is set part way into the bore and #3 and #4 bearings are put on and all three are driven in part way. Next #1 is put on and 1-4 are all driven into place, and then #5 is driven in from the rear. To try to do all this when the case is hot, it is likely the shaft would get stuck part way in and be close to impossible to get back out.

      And finally the retaining bolts also help keep the bearings in place.

      • Yes, I had forgotten that the old aluminum crankcases are very delicate, good point. I was thinking that a reproduction crankcase casting could handle some interference fit bearings, but definitely not a 100 year old casting.

  3. I don’t want to hijack the thread, but man o man, that his a fine looking machinist chest in the background of the photos. Did you have it from new, or, a ‘ hand me down’? Nice.

    • Chuck, It certainly is a outstanding tool box made of bireseye maple, and I was delighted to find it.

      I bought it at a country auction here in Vermont about 10-years ago.

      It was shop built by someone a long time ago, who either used hardware off of an old chest or sourced it somewhere else.

      You can see a larger photo of it here: http://theoldmotor.com/?p=51174

  4. Thank you for this post! I am in awe. Question: if an aluminum case is cracked or a piece is broken off, can it be welded satisfactorily? After all, these things have been soaking in oil for 100 years. Is there a way to properly weld them?

    • Bill, Not Simplex aluminum castings, because the alloy that was used for casting them is not weldable.

      Many people have tried ever since the teens’ and no one has been successful.

      This only leaves metal stitching or replacement.

      Austin Clark had new crankcase and transmission and differential patterns made in the sixties for new castings. I have machined a set of both types, and it is a very time consuming and expensive process.

      • I believe Austin Clark had the aluminum it analyzed before he went to all the expense of having the pattens made; there is an article about it in the “Antique Automobile” I think published in the 1960s.

        I am sure others have also had it tested to find out it’s make up. Regardless, every type of cleaning, preheating, and welding process has been tried in the past without success. Some aluminum solders make work, but are not strong enough to hold the crankcases halves or trans.-diff. cases together if cracked.

        Some of them are fine, but there are others that fall apart in time.

  5. David,
    Thanks for the careful documentation of this excellent Craftsmanship and painstaking restoration work. I appreciate this documentation as a valued learning resource – I am interested in the repair & restoratiin of vintage and antique Indian Motocycles. Best regards.

  6. Concerning the issue of early castings soaking in oil for 100 years. About 30 years ago I was involved with the restoration of a couple of 1911 Mercedes and the aluminum oil pans were sort of “vacuumed” in a heated chamber, then coated with a space age epoxy. I believe the company or process was called Castite. It cured the porosity issue.

    • Jerry, It is called vapor degassing and uses heat in a vacuum chamber removes most of the oil in the casting. I believe the EPA has clamped down on the process.

      This process is also a good to use before welding a casting. It has been tried on Simplex castings but the alloy was still not weldable.

  7. A beautiful job David. It just so happens that I’ll be making the same parts for my car soon and, once again, your solutions to the attendant problems are a big help.

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