Reproduction Parts for 1916-1964 Chevrolet Passenger Cars & 1918-1987 Chevrolet & GMC Trucks
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I have two questions this evening about my 28 truck project as I have been working on the engine as of late.
First question is the upper half of the center main. It has a crows foot channel in it. the two branches I will call them serve to spread oil over the whole surface of the upper bearing. The center channel is to supply oil to the lower bearing cap cross channels. I have looked at all pictures in Deans Resurrecting a 4-banger thread as well as the Schools in Session thread and watched the video by the Lunchtime Restorations guy. There are no photos in the Schools in Session thread that show direction of upper center main in the block, but in Deans thread he shows the straight channel installed so when the crank turns in its CW rotation it is 'pulling' if you will oil through that channel to the lower half. In my mind this is correct because if it were pointed the other direction as the crank turned it would just pull oil or better said maybe keep it from getting down the channel to the lower half. The Lunchtime Restorations guy clearly put his upper half center main in the opposite direction as Dean. I honestly have to say I was negligent in paying attention to the direction in my truck engine and am sure in another engine I tore down that it was the same as the Lunchtime video. The repair manual doesn't speak to direction.
I thought I could pull a clue off my old bearings by measuring the thrust faces. It would make more sense to me that the thinner thrust face would face the back of the engine because when you push the clutch in and cram the crank against the bearing it will wear. I don't see where there would be any forces wearing the front thrust much. So, with that said my thinner thrust face would put the bearing in opposite from what I think and how Dean shows his installed. (You have to look close ant this picture and then imagine the crankshaft rotation) So the question is does anyone have input as the proper orientation of the upper main half? Honestly, I trust that Dean's pictures are right. I can't imagine he wouldn't have paid attention to detail and put things back together how he took them apart and honestly it just makes sense, but I am still puzzled by my thrust face wear.
My second question is in regard to head painting. I got my head back from the machine shop yesterday and want to finish assembly of the springs and keepers. Most pictures I have seen and things I have read show the whole head being painted including the oil valleys etc under the valve cover. Is the best way to go about this to paint the head off the engine without the valves, springs, etc in place then put them in? I find myself thinking about how they would have done it at the factory. It's hard to envision them taking the time to mask off mating surfaces and rocker stands and shoving something in the valve holes so they could paint the head then assemble it and then bolt it to the engine. The Schools in Session thread doesn't clarify and I am pretty confident that that engine was painted fully assembled which means it must not have received paint in the oil valleys in the top of the head. Input would be appreciated.
Thanks, David
The best we know the engines were painted after assembly. In the six cylinder engines 1929 and newer; that included the manifolds, water pump, generator adjustment arm. Carburetor, generator, starter were not mounted when painted. I suspect that the late 4 cylinders were the same. The question remains about the side covers and valve cover. If they were not installed when painted the valve train would have over spray.
How sweet the roar of a Chevy four
Participant on Chatter since 11/22/2001
19758 posts on the former Chatter site
There was a long discussion about engine color in Ray Holland's Four Cylinder Engine Rebuild document. It's starts around page 46 and goes on until around page 52.
As for the installation direction of the top half of the main center bearing, here's another pic from the 'Resurrecting' saga that corroborates the photo posted by David above.
Cheers, Dean
Dean "Rustoholic" Meltz
San Leandro, CA
3511 posts on vccachat.org
Lurch -1927 LM one ton truck - tinyurl.com/Lurch-VCCACHAT-Gallery
Justin - 1928 AB Canopy Express (1/2 ton truck) - tinyurl.com/Justin-Stovebolt-Gallery
Speaking to the subject of center main bearing direction, you can probably match up the shells to each other by comparing thrust surfaces. If they are not installed in the block in the correct direction or the cap is backward, and assuming you're not going to line bore the block, chances are the crank will bind up before you reach full torque on the center bearing cap with shims in place. If it were me, I would set up the way I think it goes, torque the front and rear caps first, then take up the center main cap. Tighten a little, test rotation, tighten some more, test again, until I reach the desired torque and can still rotate the crank. If it suddenly binds up along the way, stop, back off, and try something else. I went through this a couple years ago on a 28 block and afterward I marked the cap and bearings for future reference.
Speaking to the subject of center main bearing direction, you can probably match up the shells to each other by comparing thrust surfaces. If they are not installed in the block in the correct direction or the cap is backward, and assuming you're not going to line bore the block, chances are the crank will bind up before you reach full torque on the center bearing cap with shims in place. If it were me, I would set up the way I think it goes, torque the front and rear caps first, then take up the center main cap. Tighten a little, test rotation, tighten some more, test again, until I reach the desired torque and can still rotate the crank. If it suddenly binds up along the way, stop, back off, and try something else. I went through this a couple years ago on a 28 block and afterward I marked the cap and bearings for future reference.
Thanks for the input Ron. As mentioned, I am able to identify the thinner thrust face on each bearing half which leads me to believe these were the sides towards the transmission. However, that wear doesn't coincide with what is the correct direction for the block half piece and which way the straight part of the crows foot is to point taking into account crank rotational direction which Dean confirms nicely what my thoughts were on that. So, the short answer is my bearing block half was put in backwards either from factory or at some point on a rework. I know my truck engine was messed with at some point as it didn't have a numbers matching head on it, and the engine I took these better main bearings out of also had indications it had been opened up (if it isn't evident I am doing a make one engine out of parts from two like Dean did in Resurrecting a 4-banger)
On another note, I can speak a little wisdom into your binding caution. I had a binding problem on the center main specifically that drove me absolutely crazy for a couple of nights. I kept playing with shims in locations to no avail and what I finally noticed is the cap bolts are not all concentric from shank to threads. At least a couple of my bolts have threads that offset by a few thous from the shank and when the bolt would go around it would cam the cap ever so slightly crooked and the bearing would bind. I had to go through all my extra bolts to find a pair that didn't do this and use them on my center cap and when I did, I got the results I was after, just wasn't confident my block bearing half was the right direction.
As to the paint, I know and have the pages saved where it discussed the paint colors in the Schools in Session thread. I understand there is still some question as to color of rocker cover specifically. I personally believe there must have been both black and green because I have both here. The black one is on a 27 engine I have. I also personally believe they were painted off the engines as there is paint color on the underside of the cover. Now that's not to say someone couldn't have done a repaint over the course of almost 100 years, but I'm doubting that because I don't think they would have left that underside lip at least unpainted and I agree that the spark plug wire conduit is black and it had to be painted off the engine thus the valve cover wouldn't be in place.
That's not all that important to me as much as to what extent the head would have gotten painted. I'm inclined to believe it was on the engine when painted I just don't know how they would have not over sprayed the rockers and valve stems and certainly wouldn't have gotten paint down in the head valley. The only way I can see that there would possibly be paint in those valleys would be when the heads were assembled they went down a line where a guy slopped some paint in there then the next guy shoved valves in the guides then the next put the springs and caps on then the head mated to the engine then the engine was sprayed with some kind of jig/cover placed over the valve stems and springs, then rockers and pushrods.
Clueless otherwise. I just know I prefer not to have bare cast to potentially rust which I feel even though it's slathered in oil, over time it will potentially do.
Maybe it's going to come down to my personal preference rather than a concourse restoration action.
Thanks,
David
That's good wisdom about bolt camming and one thing I forgot about. I thought I was having the same problem on my center main so I bought brand new grade 8 bolts and tried those, but still had some binding problems related to cap bolt clocking. I assumed new bolts would be more concentric, but perhaps I was wrong. In the end, I found a combination of old bolts and positions that achieved my goal.
Thanks,
Ron