About to have the mains rebabbitted on my 26, wondering what the optimum end play should be?
I understand the maximum is .007"
.001 would be stuck, .002 a heavy drag.
Should be set not under .003, and not over .004.
.006 is wore, and .007 is the start of Maximum wear.
I agree with Herm. :-)
Some years ago there was a series of articles in The Vintage Ford by Milt Webb on the performance of his Coupe. I remember disagreeing with his claim of 50+mph from a standard T. Jay never did publish my rebuttal. However Milt did have serious wear problem with end play on his crank, he was measuring 0.001” wear for each thousand miles he drove. Of course the speed he drove may have had something to do with the excessive wear. In the article the original specs were listed and correspond to what Herm wrote.
Dave - Forgive me for this post that somewhat detracts from your question, however the discussion that has resulted causes me some thoughts and "wonderment" in my feeble mind:
My first thought was,.... what exactly is the biggest cause of Model T crankshaft end play?
Many years ago, I was given to understand something that may, or may not, be true. I was told that a vehicle with an automatic transmission is actually easier on an engine, because of the absence of pressure against the flywheel, and hence pressure against the crankshaft thrust surface(s), each time the clutch is depressed on a standard manual shift transmission.
Accordingly, that prompts the thought that the Model A clutch is a huge improvement over the Model T clutch, in that with the Model A, the only pressure that must be absorbed by the crankshaft thrust surfaces, only occurs when the clutch pedal is depressed. The Model A clutch pressure plate internal springs keep the clutch locked up without exerting any pressure on crankshaft thrust surface. On the Model T, the single clutch spring maintains a constant pressure on the entire clutch, flywheel, crankshaft thrust surface,....ALL THE TIME,....which is what I believe contributes greatly to Model T crankshaft end play. FWIW,..... harold
I probably don't understand the metaphysics of the Model T transmission, but it seems to me there is no thrust pressure from the clutch spring when the car is in "high". The release of the multiple disc clutch when in "neutral", low and reverse means the spring tension is thrusting against the crankshaft, pushing it forward.
Rich has it right.
If the engine is in the car and the only problem with your engine is 0.007 " end play, I would just keep driving it. Assuming the Babbitt in the block is good and the engine is out, then add Babbitt to the thrust surface or replace the main bearing cap. Magnaflux the crank and have the rod journals reground if need be.
Rich is correct but the thrust is rearwards as the clutch fork compresses the spring towards the rear of the car.
Automatic transmissions that use a torque converter do not add any additional thrust to the crank other that what the engine naturally develops
Manual transmissions cause a forward thrust via the thrust bearing when the clutch pedal is depressed
The Model T transmission only adds rearward thrust when in neutral be it via the pedal pressed half way down or lever vertical. Top gear is when all the pressure is captured within the three drums and they float around the 17 - .022” or whatever the current endfloat of the unit has been set / worn to.
Just my understanding
Alan in Western Australia
It’s a great design feature as any increase in crankshaft end float caused by transmission thrust increases the clearance between the magnets and the stationary coils and Not reducing it with catastrophic results
End play wear on the rear main will be almost nothing if you pour thrust on the block, along with the cap.
Not really true in practice. There IS forward thrust on the crankshaft, caused by the constant magnetic attraction in the magneto. If you've ever looked closely at front facing side of the crank flange, you'll see a groove, sometimes deep, caused by forward thrust. Eventually, there can be contact between the magnets and coil ring.
Alan !! Thanks for pointing me in the right direction !! ; ) I got it now.
Herm. You mean some don't pour the rear main in the block correctly ?!? I can't imagine rebabbitting the block without a thrust face on the rear main !!
Jerry, must be magnetic pull then, If we've eliminated clutch and transmission pressure on the rear main - I've sure enough seen the groove on crank flanges !
Ford did not babbitt the rear main in the block for forward thrust. They only had a thrust face on the rear main cap for forward thrust.
Yes, it's the magnetic attraction.
I am suspicious that there may not be any forward thrust due to magnetic attraction of the magnets to the field coil when the engine is running. Every other clamp plate is opposite polarity and induce current into opposite wound coils. There should be a break even between half of the coils and magnets attracting/ repelling. Maybe an electrical / motor expert can enlighten us on this.
Magnetism is magnetism, whether it's standing still or in motion.
From 1919 on the crank shaft timing gear teeth were angled, so the force needed to drive the cam shaft should give a small resultant forward axial force on the crank shaft.
Make sure the thrust face on the crank flange is clean and polished, just like the mains and rods. Any grooves or ruffness will wear the thrust face on the cap faster if not. Often times the flange has a cup worn in it, no way to set proper gap if it does.
Jerry, when the magnets are rotating, approximately half the time there is no metal in front of them so there is no pull during that time. If each magnet can pull two pound then it’s a total of only sixteen pound (2 pounds x 16 / 2), which is a lot different than the 90 plus pounds to override the clutch spring when in it is in high gear.
I’m not smart enough to figure out the pull caused by the angled camshaft gears, anyone want to jump in?
When the end play increases at the front due to the clutch arrangement, the gap between the coils and magnets increase which will reduce the output of the magneto. If the crank moves forward, the magnets will hit the coils - time for rebuild.
I have the engine out of the car and disassembled,
the crankshaft end play was .007" when I checked before removing the crank...the reason I asked about the optimum end play is I am about to have the mains re poured, so I want to know what specs to request......003" - .004" sounds right to me . This should allow enough clearance for lubrication.
Just an observation, my mag seemed to work just fine at .007" end play.
On the subject of Babbitt pouring, does anyone know of an experienced shop or individual in my neck-o-the woods that they can recommend. The model T club I belong to has only one guy doing this kind of work and he is just starting out.
No offense to the guy, but I am looking for someone who has a proven track record.
I am in the interior of British Columbia near Kamloops, and I am willing to travel within reason.
Yes, I'm sure the clutch spring applies way more pressure than the magnets do. But the magnets do it constantly, while the clutch spring only momentarily. Plus, as mentioned above, there is only 1/2 the babbitt thrust surface available to take up the magnetic thrust load than there is to take up the clutch thrust load.
Just about all the thrust wear on the rear main of a Model T is on the front end of the block.
That all comes from anytime the car is in neutral, being stopped, or when driving, shifting, ect.
When the motors were new, the blocks, along with the caps had even thrust on them. Yes they used the block ends as a cast iron thrust.
When you cut the thrust, on a low mileage block, the rear will line up perfect, with the cap, if you put the crank where it belongs, and use the original crank.
I have had two blocks that were perfect, the rest of the low mileage blocks matched on the rear, but were worn a few thousandths to much to match in the front of the rear main.
To prove that the rear main wears more in front Jerry, any accessories I have seen to hold end play, takes play out by holding the crank forward. Some use the crank pulley, others use the center main.
Here are some pictures of a 1913 very low mileage engine we done about 5 years ago. The motor blew many years ago and was kept with the very low mileage car.
very interesting statement if I understand your are saying the width of the bore in the cast iron block would be 3.125" (factory drawing of width of the rear crank shaft bearing) less the .003" to .004" thrust clearance.
Is there a drawing of the block to support the statement, I Never have seen one so that is why the question..
I’d sure like to see the block blueprint with those dimensions...
Mike, the 1913 block, shown in pictures here, is one of the two I have had, that the block comes out with the thrust of the cap, on both ends.
The thrust should have been cut at the same time at the Factory so they were even. Would have saved a lot of time, also
Don't know of any spec's, but the crank fits the block perfect.
Most blocks are wore on the ends. The front is always wore more.
Believe it or not, but that is what Ford did .002" -.004" end play between the crank flange and block before even considering setting up the cap with the same clearance.
It's actually a bit hard to interpret the instructions, after setting the crank per-say, on whether there is, what is, or if there is clearance on the front of the block bearing??
This was the Old way of doing engine rebuilding in the Ford Dealerships.
In the 20's when K.R. Wilson started making bearing tools, they got rid of all the out dated engine building ideas.
Great info posted here. BUT! I bet 80-90% of the guys posting here don't drive more the a few hundred miles a year. As long the the crank is centered in the rear main and has the proper gap, that will be great for most of us. We are talking about and engine that at it most will turn in the max 1400-1500 RPM range. Once the gap has been set for the magneto, the engine should be good for many years. While the KRW tools are great, part of the package was the gap gauge and as many out there don't have one or access to one we have to set our gap by trial and error so getting things setup to be able to use that tool(s) per the KRW way is not as necessary in my OP.
Heck, my block had original babbitt in it. I installed rebabbitted caps, hand filed the thrust and drove the car in the 1000's of miles. I would still be driving it if the nylon timing gear had not come apart and plugged the center main oil hole. Sometimes getting thinks to within a nats whisker is just not needed.
I do want to add, I think Herm, does great work and is a credit to the hobby. Thank you for posting the pictures and information.
(Message edited by redmodelt on November 23, 2017)
I don't really see the connection of K.R. Wilson tools has on determining wether Ford used the cast block as part of the thrust bearing.
Wasn't trying to make a connection there.
The connection is between the old way of building bearings, and the new way K.R. Wilson did. Which is entirely different.
That ‘13 block has late style bearing caps. Do you think it was babbitted once before, or did you scrap the original caps for some reason?
We scraped the caps that came with the block.
It had the original Babbitt until they fixed the hole in the block, from the rod.
The early style of caps are junk, and have no support for the suspended thick Babbitt on the sides.
No, it had never been poured, as the rear main cast was not wore. So with a new scat crank with a standard length rear main, it fit the cast iron thrust.
Good point that you made on the front/rear thrust discussion, when you mentioned that all the wear take-up gadgets work on the front end of the main. Thanks!