Motor Question

LeroyM

LeroyM

Senior Member
I have a Model B motor in my coupe. I went this morning for a 20 mile or so drive. I was crusing along nicely at around 50 to 55mph. All of a sudden I start to hear a profound knock. So I slow down and pull over, at idle I hear no knock, nothing over heated or no oil leaking or anything like that. I back up and give it some gas and I get a good puff of white smoke. Driving it though it doesn't smoke at all. Up until about 40 mph everything sounds good, over 40 mph or getting down on it I hear a profound knock again. I made it home, unhooked the new fan belt to see if it maybe was the generator or water pump, but wasn't any of those.

I'm thinking babbit maybe or oil pump, but won't know until I drop the oil pan which I plan on doing tomorrow or next week. Any ideas on what it might be before I drop the oil pan or pull the motor? If it is the babbit I'm thinking now would be a good time to look into insert bearings but couldn't find them in the catalogs for the Model B motors. Who sells them?

Any help would be appreciated.

Thanks.
 
Bearings are available from Ant. Eng. Rebuilding or from NAPA in the form of 350 ci SB Chevy connecting rod bearings.

White smoke is generally related to water. Pull the plugs and see if any of them look like they have been ""steam cleaned". Is it possible you have detonated it?

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I had a problem with water getting up on the valves and pistons. A few weeks ago I pulled the head and threaded the two Model B steam port holes and put in two socket cap screws along with a new modern head gasket. I'm running a Snyder's high compression head by the way. This was the first trip with it since then. Like I say it was doing good for about 20 miles at 50 to 55mph, then all of a sudden I got a knock.

What bearings would I use for the mains? I was quoted a few years ago for $400 to do babbitt on another motor. What kind of price would I be looking at if I was to go with inserts?
 
I just told you, ...SB 350ci bearings. $400 is a great price. You won't be able to do the insert conversion for anywhere near that. My suggestion is to find someone who has done the conversion and understands how to bore the block and undercut it because a machine shop that has not done the conversion could have a malfunction which could cost you the block.

On the head, are you using a B head gasket? If so, ...which one? Any chance the head gasket lost it torque and started leaking water? If enough water enters the combustion chamber, the heated water turns to steam which has incredible pressure. Can you back up before a few weeks ago and tell us what happened originally? Tell us why you plugged the steam holes too, --and exactly how you installed them please.



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Well I threaded and screwed in two 5/16" set cap screws into the steam holes of the Model B motor because I was getting water to the two valves next to those two steam holes and it was running into the pistons. I used a Model A head gasket with the Snyder's head before I plugged them.

After I plugged them I called Snyder's and told them what was going on and that I was running a Model B motor with their head. I asked which gasket to use since I was going to plug the two steam holes. They said use the modern B gasket which I did.

After plugging them I followed the directions on the gasket. I torqued the head to 55 lbs then I ran it for 15 minutes at a fast idle. Then I waited until the next day and retorqued all the stud bolts down to 55 lbs. I took it for a short run yesterday, no problems at all until today when I took about 20 mile or so drive.

That's the only thing that has been done to the motor.
 
So if you ran cap screws down into holes you threaded, what did you do with the heads of the bolts? Did you grind them down, leave them alone, or did you machine them flat??

Pull the plugs and see what coloring you have. Look close for detonation specks too.

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The socket cap screws had no head on them. They were 5/16" x 5/16" and threaded all the way. I ran them down flat and there was nothing sticking up over the deck of the block.
 
LeroyM said:
The socket cap screws had no head on them. They were 5/16" x 5/16" and threaded all the way. I ran them down flat and there was nothing sticking up over the deck of the block.
Click to expand...

Just for your information, Cap screws all have heads thus the name cap.
Set screws do not have a Cap or head.

So technically you used a hex set screw.
 
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ModelBwaterhole2.jpg


I did the same fix for a friend that has a Model B engine and is using a Model A high compression "B" head, also know as the "police head". I ran the hex socket set screws just below the deck surface then filled it in with JB Weld, which I leveled using a razor blade. I use the copper Model A gasket with Copper Coat sprayed on both sides.

Does you B crank have counterweights?

From your description, it sounds like the center main babbit is bad.
 
I have some question whether it is a bearing problem, especially if you do not hear it at idle and it came on loud all of a sudden. Do you get the knock if you advance the timing at idle? Does it come on at high rpm sitting still? If so, is there any change when you disconnect a spark plug? Since the head was the recent change, I would pull the head and look at the top end, then pull the pan and start measuring bearings before making a decision to rebabbitt or do inserts.
 
Sounds like the head gasket blew. Pull the plugs and hold your thumb over the plug hole to test the compression. If the gasket is blown it will not have any compression and sound off in the adjacent cylinder.
 
I pulled the motor and transmission today and found out what the problem was. It was two problems really. The first problem was 3 of the 4 caps on the rods were loose to were you could shake them side to side and I could hear the same knock I was hearing yesterday from that. The babbitt looked good and there was only a pinch of fine grain babbitt in the oil pan dipper tray. Some of the rods had 4 shims on each side and some had 3. I ended up pulling one set of shims out of one rod after torquing it to 50 lbs because the motor was to tight to turn over with the hand crank.

The other problem I had was the pilot bearing that goes in the flywheel had come loose and was frozen to the input shaft on the transmission. I still haven't got that off the input shaft after breaking the bearing trying to get it loose, the case hardened piece of the bearing is still stuck to the input shaft on the transmission. I sprayed it with pb blaster and left it sitting over night while I get some gaskets and a pilot bearing ordered to put everything back together next week.
 
LeroyM , To remove the bearing race cover with a rag and hold a large hammer or block of steel on one side of the bearing and strike the other side with a hammer to break or crack the race. Be sure to wear saftey glasses and heavy gloves in case a splinter chips off. The pilot shaft may be damaged from the race welding itself to it. I have repaired the bearing surface by brazing up the damage and turning back to size in a lathe. If you have to replace the piolot shaft go ahead and replace the roller bearings and the shafts, use the shafts with the "O" rings to help prevent leaks Good luck , Bubby Sharp in KY
 
I have the pilot bearing off. It's just the center steel piece that's stuck to the input shaft. I'm hoping and trying not to screw up the input shaft. That's one reason why I left it until another day. I'm running a 39 transmission so I have to take my time with it. I'm hoping I can bust it loose with a good sharp cold chisel. Wish me luck. lol
 
If you have an oxy-acc torch, I'd heat the race to remove it. If you don't have a torch, then I'd use a Dremel to grind almost all the way through on one side, then use a dull chisel to split it.
 
Use a Dremmel with cutting wheel. You don't need to go all the way through. You can grab it with a Vise Grip or a pipe wrench and twist it and it should break off. The bearing race, not the input shaft. My 2¢.
 
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