1951 Commodore 8

[Deleted User]

I have a 1951 commodore 8. The problem I have is that it has some loose main bearings and some valve noise. That is a shame because the engine does not smoke a bit and has even compression and runs smooth as silk. The valve noise is not as big of a concern as the main bearings because I was told that if you adjust the valves and the valves still are noisy that the lifters are probably worn on the bottom side. I can take them out and have them refaced but I hear that it is impossible to find new main bearings anymore. I was glad to find out that even though they are babbit bearings that they can be removed by taking a small screw out of the bearing cap that holds them in. I have'nt tore it down yet but I am sure what the noise is and I don't know what the crankshaft and bearings look like yet but I'm am going to tare it down in the next couple of days. Does anyone know where a set of main bearings might be or know of any ways to fix this problem without taking the engine out and having new babbits poured? That is more expense than I can afford right now. Thanks, David McGill

Jon B

For many new Hudson engine parts you can try Dale Cooper at http://www.hudsonmotorcarco.com/ . I believe he has main bearing sets. I am sure there are other sources, his just came to mind on the spur of the moment.



Are you in the Hudson club? If not, you may want to join, for it's a great clearinghouse for parts sources and tech. information. http://www.hudsonclub.org/

Geoff

David, unfortunately, unlike the earlier 8 cylinder engines prior to 1937, there is no provision for adjustment of the bearings. How do you know it is the main bearings that are noisy? There are ways around it if the mains are worn, but usually by the time they are noisy they have also started to fail, so adjustment may not be an option. As far as valves are concerned, yes if the lifters are worn then they will continue to make noise even if the clearances are correct, but a quick adjustment of the clearance should sort that out. It is not possible to change the main bearings unless the crankshaft is taken out.

Geoff.

[Deleted User]

Thanks for your quick reply. I am going a lot on past experience, athough I have never delt with a splasher babbit bearing engine before. I'm not 100% sure it is the mains but when I first start it, I can hear a thump for about a minute, then it starts to quiet down. I let it set there and run at a fast idle for about a half hour and when I idled it down, I could hear the thumping again. I let it set for a little while and started it back up and yes it was thumping again. Since it don't smoke,has good even compression and runs smooth as silk and not much blow by either, that is why I think it is the main bearings. I've worked on a lot of engines over the years and the sound, sounds familiar but like I said, I have never delt with a splasher babbit bearing engine before. Due to the good compression etc. I don't think it is a busted piston. Do you know of anything else it could be.

Park_W

David, if more investigating does indicate the main bearings are bad, other than the extra work of pulling the engine, it's not all that bad to deal with. There are good folks who rebabbitt your main bearing shells to a "semi-finished" size, (last ones I had done cost $35 each), then a local machine shop will line bore the rebabbitted bearing shells to the correct size for your crankshaft journals. I would not try just replacing the main bearings without going through the line boring process, as most of these blocks "settle in" as they age, so the main bearing "saddles" are no longer concentric. Then when you just install new bearings and fit them to the proper clearance, the misalignment of the block will cause the bearings to bind on the crank. Then your only choice is to loosen them so they don't bind, and now you're running with maybe .003 clearance when they should be at .0005 to .001. Long life has been compromised. Really the biggest challenge is finding a shop that has a suitable boring bar to do a straight eight block. And if you do end up having to shop around for one to do this work, be sure they know you're talking about line boring the babbit bearing material, not the cast iron block saddles (the latter is done in more modern engines to correct block misalignment). I've got to do my '47 Com 8 this summer, and when I started asking around I found there's a shop right here in the Charlotte area that does line boring of this type engine. So if you're faced with this work, just do a little networking with shops in your area.

Ol racer

Just a thought regarding the Thump when first started... Many modern engines thump when first started after an oil change then quiet right down as builds oil pressure with no apparent damage to brgs or crank..



I didnt read anything regarding your oil pressure.... I have no experience with 8's but believe the mains are pressurized so I suggest checking the pressure with a screw in gauge at the Sender.. Maybe mains are not worn just not getting enough oil...Either worn or low pressure would cause thump...Maybe you might be lucky to quiet them down with better pressure...



(My luck it would need torn down & rebabbitted)



Regarding the valves I wouldnt wory about them because its better to have them on the 'loose' (noisy) side than tight & quiet.....

Unknown

The mains are not pressurerized. Oil the same as the splasher 6. The pump only puts oil to the top pan on these engines and with very little presssure.

Geoff

bmcgill wrote:

Thanks for your quick reply. I am going a lot on past experience, athough I have never delt with a splasher babbit bearing engine before. I'm not 100% sure it is the mains but when I first start it, I can hear a thump for about a minute, then it starts to quiet down. I let it set there and run at a fast idle for about a half hour and when I idled it down, I could hear the thumping again. I let it set for a little while and started it back up and yes it was thumping again. Since it don't smoke,has good even compression and runs smooth as silk and not much blow by either, that is why I think it is the main bearings. I've worked on a lot of engines over the years and the sound, sounds familiar but like I said, I have never delt with a splasher babbit bearing engine before. Due to the good compression etc. I don't think it is a busted piston. Do you know of anything else it could be.

Normally a worn main bearing will cause a heavy knock under load. However, it could be that the bearing is in fact beyond redemption if it is knocking when the engine is not working. There is really now way of finding out what is wrong without taking the sump off and checking each bearing. However, before doing this I would set the engine to the speed where it knocks, and short out each plug in turn and see if this eliminates the knock. If it does, it most likely indicates a loose connecting rod. If this is the case, then again you have to remove the sump and inspect the rod bearing. You have no option but to replace it if this is the case, as there is no provision for adjustment. If it is in fact a loose main bearing, and the babbit is still serviceable you can ascertain how much clearance it has by using a strip of cooking foil , folded over 4 times to give you .002", and insert in the bearing and bolt it up and try turning the engine over. (The foil is half a thousands of an inch thick). If it binds, the clearance is correct. If it turns freely, then use a thicker folded piece of foil, until you find out at what clearance the crank binds. If for instance you find you have .006" clearance, then you can insert two strips of .003" brass shim between the shell and the cap, and this will reduce the clearance. You will have to file a small amount off the ends of the shell where they butt together. Takes a bit of fiddling, but you can get it pretty right with some patience. Good luck,

Geoff.

[Deleted User]

Thanks again Geoff. I wondered about using shims behind the bearing shell. I have a parts car with a complete engine. If my bearings are totally shot and the ones in the parts car are good and the same size, could I just swap them out and use some plastiguage to check the clearance?

[Deleted User]

Yes I know that. All the oil pump does is pump oil up into the dipper tray.

[Deleted User]

Thanks for your advice but I believe that all the oil pump does is pump oil up into the dipper tray. I was told this by Doug Waldrick who restores Hudsons and does mechanical work on them for a living. You might have heard of him.

Geoff

bmcgill wrote:

Thanks again Geoff. I wondered about using shims behind the bearing shell. I have a parts car with a complete engine. If my bearings are totally shot and the ones in the parts car are good and the same size, could I just swap them out and use some plastiguage to check the clearance?

Problem is you can't take the top bearing shell out, as it is screwed into the block. You have to remove the crankshaft to replace the main bearings.

Geoff.

[Deleted User]

Hi Geoff. I hate to hear that you can't get the top bearing out but a guy named Doug Waldrick who restores and does mechanical work on Hudsons for a living said that it would come out, to just use a blunt ended object to not damage the soft babbit and tap on either side and it would come out.

Thanks,

Buck McGill

Unknown

Takes a little more than a few lite taps. Got to shear the 1/4 inch flat hear brass screw that holds the top half in. Unless it has already been sheared or left out before.