MTFCA Forum

So who has the data on rod bearings?

What lives longest?

1. X'd bearing - no holes
2. X'd bearing with top hole drilled
3. X'd bearing with bottom hole & chevy scoops
4. Smooth bearing, no x - no holes
5. Smooth, no x, top hole
6. Smooth no x, bottom hole & scoops

I'm not sure that any specific one would work best in all applications. More oil access (Xs, scoops, etc) might be best for higher speeds at moderate loads, and a full plain bearing might be better for a engine running at lower speeds and higher loads, especially in a warmer environment. You're trying to balance oil access and bearing surface. Both are critical to longevity.

Since my engine was rebuilt at the end of 2009, I've done approx. 31,000 km (19,375 mi). Bearings were X'd and dippers fitted. It still runs as smooth as right after the rebuild. The pan cover has not been off the engine since then, and I drive the car hard and fast.

I have no X and no holes. I adjusted rod bearings a few weeks ago and now only numbers 1 and 4 still have shims. I will be replacing three rods (one is practically new) in the next teardown. So, I will be watching this thread.

At the end of Model T production, or near abouts, did Ford come out with rods with the cast-in oil scoop similar to the Model A connecting rods? I have a set of them in my 26 coupe but don't know if they were original Ford or aftermarket. My understanding is they were original Ford.

I believe that no X is better. I base my opinion on my understanding of hydrodynamic lubrication. I like holes and scoops.

But the best things to do are: keep the oil clean and maintain proper oil level.

The question this topic raises is, will this thread go on as long as the best oil topic often does.

Art Mirtes

"replacing three rods (one is practically new) in the next teardown"

Something is very wrong there.

(?) Rod alignment, type of oil, oil delivery, (pipe) condition of the crankpins.... Rod bearings won't last long on flat crankpins.
Plain bearings especially need a slight chamfer at the parting line to allow oil access.

Some type of scoop can be advantageous, but it needs to be narrow, like the sheet metal scoops used on 1940's Chevrolet rods. A scoop can cut a trough in the oil in the pan dip at higher rpm, especially if the oil is too thick or is cold. In such a case, the bearing can starve for oil. It takes some time for the oil in the dip to flow back once the scoop has passed through it. Cold oil or thick oil takes longer to recover after the rod dipper moves through. If I used scoops, I'd want an auxiliary oiler and high quality, light bodied oil.

The Chevrolet scoops are carefully designed to work to the best advantage. I would not alter one in any way other than as necessary to mount it on the T rod. The last thing you want to do is to stick a screwdriver in the scoop and twist it to widen the slot.

Two of the choices, X'd with upper holes drilled, and X'd with dippers/scoops, got some responses about Oil vs Bearing surface area. My thought would be this.
IF the upper holes drilled indicates that the upper bearing is X'd, this would reduce bearing surface where it's really needed, in the upper bearing. Power stroke pressure driving on the, now reduced, upper bearing surface, would be increased due to the reduction. This would cause a reduction in bearing life.
The bottom bearing surface X'd, and holes with dippers oiling from the bottom, would seem like a win/win. More oil is supplied to cushion and cool. And, the loss in bearing surface area would have no, or very little, negative effect as the lower bearing surface only pulls the piston down on the intake stroke. The lower bearing is pretty much just along for the ride.
Maury Dean

Dean and Art have posted some very true responses. There's much to consider and understand and not just more is better...

I measured the amount of Babbitt that is removed from the new rods available from the vendors. With very careful measurements of the large diameter holes and wide X grooves we determined ONE Whole Square Inch of Babbitt was removed from the bearing surface of the rod and in our opinion would limit the service life!

I agree with Dean that the upper surface receives the most force on the power stroke. The holes and grooves do allow the oil to escape and drain out as well, which puts more pressure on the oil film that keeps the surfaces separated and limits wear.
Attention to details such as the chamfering of the mating surfaces like Art mentioned is very important. This allows oil flow infiltration as the pressure is relieved on each stroke. Also very important is the smoothness of rounded side of the bearing surface. Many times there is a small sharp edge there and will effect the ingress of oil migration into the bearing.

I don't believe there is enough of an oil puddle when the engine is running at speed for the dipper to scoop up any significant amount of oil although some of the oil mist will be captured.

If you are going to run dippers and X'ing I would suggest to severely limit the size.
YMMV I do know some Montana 500 cars run without.

Ford tried twice with a X'd dipper rod and both times failed to prove to be successful. The first of the T's and the last of the T's with the X rods.

The load on a rod bearing changes constantly. That helps distribute oil.

I've thought about this for years. No X will give you more bearing surface, and that's the way Ford did it.

I have done Xs but quite small in size, I have dippers and set all the bearings at 1.5 thou with timesaver. No idea how good it is yet as still a couple of weeks from first engine run - Too many projects on the go at once.

What I will be doing in addition to the high capacity outside oil line with scoop in hogshead, is fitting an oil pump and filter after the first 100 miles. My idea is to take oil from sump, run it through filter and pump and stick it back into the sump. Essentially I will be polishing the oil and can do it whilst running or after running. This should mean more than a thousand miles between oil changes will be possible and the oil should always be quite clean rather than having oil that gets gradually worse over a short period and needs changing at 2-400 miles. The electric oil pump is expensive, but should pay for itself over time as I save on oil changes and hopefully have a healthier engine for longer. Not sure Henry would approve and some may say that it is unnecessary, but I think filters are a good idea, even fitted one to my Continental A65. I certainly would not drive my Volvo without a filter.

Here’s a question, if the oil system in a T is not a sealed system & you’re using a splash system with dippers is the oil movement considered hydraulic or pneumatic?

Dynamic. The rods (and dippers, if so equipped) hits the oil pools in the pan, splashing it to the cylinder walls and internals... the magnets (or dippers, if sans-magnets) literally throw a shower of oil into the oil pick up tube and over the transmission... If you've ever made the mistake of running your car with the band inspection cover off, you won't do it a second time. What a mess!!!!!

Literally, it's an oil bath, engineered to sling oil literally everywhere inside the engine and transmission. Think of a tire hitting a puddle - it's the same thing each time a rod cap hits that puddle of oil in the inspection cover.

I'd love to see acrylic windows or even an acrylic pan on a T... between the engineered oil shower and the feed tube, I surmise oil went everywhere in the "splash" (aptly named) system. The only issue would be in an aftermarket overhead valve or cam engine, and then you need something to get the oil over the pistons to the valve train... or in a competition motor, where pressure oil to the mains and rods would help keep the oil film there...

So our T engines are following Bernoulli’s law on dynamic pressure in the splash system, right? If that’s true then not having an exit for the oil (like a hole in the upper portion of the rod saddle) reduces the amount of lubricant. if you have dippers & just a hole in the cap only is there enough clearance between the rod & crank to allow oil to flow in?

The portion of the bearing with the greatest load is on the rod side. To reduce wear on the rod side, you want to have a thin film of oil separating the babbitt from the crank journal. Bearing clearance is greatest on the cap side and tapers down towards the rod side. As the journal rotates, it carries along with it a portion of oil. That oil is carried into the tapering down clearance. As the clearance reduces, so too does the volume that contains the oil. The ever decreasing volume applies pressure to the oil. The oil pressure, ideally, becomes great enough to overcome the load on the bearing, to the extent that the oil creates a hydraulic cushion, keeping the rod babbitt from touching the crank journal. When you cut grooves in the rod-end babbitt, and drill holes in the rods, you're NOT "letting oil into the bearing", you're letting oil out of the bearing and thereby relieving the desired hydrostatic pressure needed for a proper oil film to be maintained. Having dippers and grooves in the cap side of the bearing I see no problem with.

If I would dig around in my old books of some 50 years ago when I did the study of The science of Engineering, I could get the facts correct but I'll just rely on memory for this. In Hydrodynamic lubrication the unbroken film or layer of oil which of course is the load taken by the oil film, can reach internal pressures around 600psi. In other words, as Ford found out in the first engines, in a surface area of a T bearing size, you don't want to have away for the pressure to demise. A leaky garden hose won't run a sprinkler to it's maximum efficiency.

6 and then 4.
I just found an old thread discussing theis and above was the conslusion.

Model T crank pins aren't very big. That reduces bearing area, but also reduces weight and reduces rubbing speed at any given RPM.

My inclination would be to lightly groove the cap and lightly chamfer the parting edges while leaving the upper bearing half plain. If you want over 2,000 RPM on any sustained basis, or make higher than about 30 horsepower, you probably need an oil pump to feed rods and mains.

When I finally get mine running, I may fit a temporary Perspex cover to sump to see how it all works and film it. That won’t answer the debate above, but would be interesting - also to see how much oil my large capacity outside oil line delivers.

The older forum posts from early 2010s had a very large heated debate on this. Rather comical and cranky at times, but also a bit divisive. For better or worse after reading all that ( and after sometime to de-stress) I drilled my caps, fitted dippers and x’d the rods. I am not sure I would do that now.

Here is a link to what led me to do mine (note, it makes the political threads look quite tame):
http://www.mtfca.com/discus/messages/50 ... 1426139022

I read the above link. Herm was correct about one thing. He ran his car with a waterpump.

I continue to think that X ing is not beneficial, dippers and properly placed holes are beneficial.

Art Mirtes

The dippers available are junk soft. They mash out from the nut torquing. The dipper scoops can/do come loose & can detach.
Then they end up on the flywheel. BAD NEWS! Not to mention the nuts can loose their torque.
The best scoops I have seen were 45 degree zerk bodies threaded into the caps.

My car has a high volume Texas T oiler installed. It has a stock magneto. I found it necessary to reduce the oil flow by restricting the tube in order to prevent over-oiling and smoking at idle. The car has run several thousand miles since with no issues and no more smoke. All 4 plugs run clean. I often drive the car at 40 to 45 MPH for miles on end.

Interesting that John endorses the zerk conversion dippers, I've done a lot of engine rebuilds over a long time and would have to say, although I've only come across the zerk ones a couple of times, they could be found in the pan when stripping the engine.

I used babbitted model A style new rods available from Snyder. I still believe they are or were the best you could do!

John Warren,
Those were the rods I had and posted about earlier in this thread. I sent mine back. I measured 1 SQ. INCH of Babbitt material had been removed for the extra large holes and super wide Xing grooves!!! I did like the bolts and dipper design though.
YMMV