Kohnke Rebabbitting
Well-known member
This time we will talk about the heart of the engine, the Crankshaft. There are a lot of ways to grind a crank, but many are done sloppy, lack of know how, using a wore out grinder, or they just don't care, or try to cheat on Quality. Just because a crank Journal looks shiny, does not mean it is good, unless checked with a Mic. Many a crank has come through hear, with a 1 and 1/2 thousandths Tapor, on a brand new grind. Ya, we have to do them over.
The only crank I have this week end, is a Model T, I poured, and align Bored, but the steps are the same to follow for any crank.
I have 10 pictures I can explain better with. This crank was ground by Vern, the shop Forman, at Arnold Motors, in Fort Dodge Iowa. He does all Block, and Crank Machining, on our engines we rebuild, as our Main work is Babbitt Bearings for 44 years.
Thanks Herm.
Picture No. 1 = Shows a clean, bead blasted crank, as all dirt, rust, grease, oil should be removed be fore crack checking, and the crank should be done dry, as any water, or oil can cause a crack to be missed, by a magnet, and iron particles, but not so much by Black Light, as Vern uses.
Picture No. 2 = Shows the rear flange was ground true, he took off .004 thousandths, to true it, or the flywheel will not run in a true plane, as any angle may give you vibration, and magneto clearance problems. Yes, the flywheel, and main shaft have to be checked also.
Picture No. 3 = Shows the correct Radius put back on the crank journal, as it should be. Guys, this is very important, as if the Radius, is NOT put back, the crank will break, and that is not if, it is when. The reason some Guys DON"T put back the Radius, is they have to have a flat stone to grind the Journal, and when the grinding is done, they have to Radius the stone, and that cost them, and so they just grind up to the Radius, and stop, and that leaves a sharp right angle, and a place for a crack to start.
Picture No. 4 = Shows the center Main Journal, for Radius, and crank Polish, and the flash on the camera, does not do it justice, as all Verns cranks are a high Polish. They need to be that way, to cut wear, and friction, that causes excess Heat in the bearing. J.V., that is what I was talking about in a post, some thing that is put on a bearing to run it in, what does that do to the High Luster, needed, on crank, and bearing. What a Shame!
Picture No. 5 = Showes, the most important Thing, as well as Picture No. 2 for getting the center line to grind a crank, dead center, of the crank. Vern checks the centering holes on the crank with the grinder, so they fit good only, with out burs only, as the Crank grinder does not turn the centers in the holes, they just hold the crank firm, and then the chucks that hold the centers, do the adjusting. So, the rear of the crank in not indicated off a wore Main Journal, but the out side of the rear flange, as that is the true center of the rear of the crank. On the front, the surface that holds the crank gear, is what you have to indicate off in the front, or in this cast, the time gears will have run out. We had a babbitt job come through here about 5 Months ago, that lasted about 50 miles, before the babbitt gave up, and after checking the crank, you could see they didn;t take the gear off to grind the crank, and the gear was .003 thousandths off center.
Picture No. 6= Shows the seal area of the crank, and where the belt pulley goes on, was ground about .010 thousandths, so a New seal will not leak, and the Pulley, will run true.
Picture No. No. 7 & 8= Show the rod Journals, Finish, and Radius.
Pictures 9 & 10 = Show Finish, Radius, and the Crank thrust Grinding. Thanks Herm.
Attached Thumbnails
The only crank I have this week end, is a Model T, I poured, and align Bored, but the steps are the same to follow for any crank.
I have 10 pictures I can explain better with. This crank was ground by Vern, the shop Forman, at Arnold Motors, in Fort Dodge Iowa. He does all Block, and Crank Machining, on our engines we rebuild, as our Main work is Babbitt Bearings for 44 years.
Thanks Herm.
Picture No. 1 = Shows a clean, bead blasted crank, as all dirt, rust, grease, oil should be removed be fore crack checking, and the crank should be done dry, as any water, or oil can cause a crack to be missed, by a magnet, and iron particles, but not so much by Black Light, as Vern uses.
Picture No. 2 = Shows the rear flange was ground true, he took off .004 thousandths, to true it, or the flywheel will not run in a true plane, as any angle may give you vibration, and magneto clearance problems. Yes, the flywheel, and main shaft have to be checked also.
Picture No. 3 = Shows the correct Radius put back on the crank journal, as it should be. Guys, this is very important, as if the Radius, is NOT put back, the crank will break, and that is not if, it is when. The reason some Guys DON"T put back the Radius, is they have to have a flat stone to grind the Journal, and when the grinding is done, they have to Radius the stone, and that cost them, and so they just grind up to the Radius, and stop, and that leaves a sharp right angle, and a place for a crack to start.
Picture No. 4 = Shows the center Main Journal, for Radius, and crank Polish, and the flash on the camera, does not do it justice, as all Verns cranks are a high Polish. They need to be that way, to cut wear, and friction, that causes excess Heat in the bearing. J.V., that is what I was talking about in a post, some thing that is put on a bearing to run it in, what does that do to the High Luster, needed, on crank, and bearing. What a Shame!
Picture No. 5 = Showes, the most important Thing, as well as Picture No. 2 for getting the center line to grind a crank, dead center, of the crank. Vern checks the centering holes on the crank with the grinder, so they fit good only, with out burs only, as the Crank grinder does not turn the centers in the holes, they just hold the crank firm, and then the chucks that hold the centers, do the adjusting. So, the rear of the crank in not indicated off a wore Main Journal, but the out side of the rear flange, as that is the true center of the rear of the crank. On the front, the surface that holds the crank gear, is what you have to indicate off in the front, or in this cast, the time gears will have run out. We had a babbitt job come through here about 5 Months ago, that lasted about 50 miles, before the babbitt gave up, and after checking the crank, you could see they didn;t take the gear off to grind the crank, and the gear was .003 thousandths off center.
Picture No. 6= Shows the seal area of the crank, and where the belt pulley goes on, was ground about .010 thousandths, so a New seal will not leak, and the Pulley, will run true.
Picture No. No. 7 & 8= Show the rod Journals, Finish, and Radius.
Pictures 9 & 10 = Show Finish, Radius, and the Crank thrust Grinding. Thanks Herm.
Attached Thumbnails
