engine knock 1949 331

[49 Convertible]

Upon returning home from the GN in Las Vegas (300 miles each way) I developed an engine knock which seems to be consistent.  Pulled the pan (per Jay's instructions) and checked each and every bearing, actually pulled all 16 and measured each journal and found no undue wear or deformity, Infact engine lookes like new (complete rebuild about 3000 miles).  Have not put pan back up but have decided to ask for SUGGESTIONS AS TO KNOCK before putting pan back up and/or pulling heads.

[Dan LeBlanc]

Cracked ring gear?

Flexplate tight at transmission?

Cracked water pump pulley?  (went through this on someone's 49 last summer)

[Jay Friedman]

Herman,

Sorry you had to go to all that trouble taking down the pan as per my instructions.

Another suggestion besides Dan's.  Make sure there isn't a leak in the vacuum system for the windshield wipers and the antenna.  When there is a vacuum leak--caused by a loose or faulty hose, for example--the vacuum pump that is part of the fuel pump can make a noise which closely mimics an engine bearing knock.  I've been scared by this more than once. 

I've also had engine's make a knocking sound when the initial distributor timing was "too advanced".  Check it with a timing light to make sure it is on the "A" mark and no further. 

I'd like to also suggest that with the motor running and when the knock can be heard, you go over the block, the valve covers and rotating accessories (water pump, generator, etc.) with a mechanic's stethoscope. 

[49 Convertible]

Thans Jay and Dan.  Am going to check out all vacuum connections and pull valve covers before putting pan up just in case the valve train has an issue.  Am also going to check out fuel pump as I had a similar problem when I first installed the pumpit  some 6 years ago and had it re rebuilt and seemed to stop the knock.  Recently sent it back for inspection as had a  leak down issue when hot.  Installed the pump and did not appear to be an issue but who knows.  Might  just look for a core and have it rebuilt as most will just rebuilt your core

herman

[49 Convertible]

Further to engine knock in 1949 331 engine.

After removing the pan and replacing all the rod bearings (old ones in fine shape) I decided to buton up the lower half and have a listen to the motor again.  Guess what the knock was still there.  After consulting with a number of Cadillac owners and engine mechanics it was decided to check compression and do the spark wire removal by cylinder to determine if knock changed.  Lo and behold #3 cylinder knock changed a bit.  We had determined that #3 could be the problem before tear down but rod bearings did not show any sign of wear.  This time removed pan etc and intake manifold and removed d/s head.  Checked push rods(perfect), lifters (perfect) checked rocker arm shaft and towers (perfect).  Removed #3 rod cap and pushed piston out of cylinder and GUESS WHAT after removing the the wrist pin from the piston I noted the bushing had cracked and there was piston rod wobble.  The bushing when pressed out had shown that it was spinning in the rod and had scored the rod where the pin goes through the bushing.  Talked with my trustworthy engine rebuilder (now does mostly racing engines) and took rod to him and he stated that in over 30 years of engine rebuilding had only seen this once before.  Am waiting for a bushing after honing out the rod or a new rod and bushing and hope this solves the problem.  Will give conclusion when I button up engine again.

[kav]

keep us posted I have a similar problem on a freshly rebuilt 331 .

[49 Convertible]

Well, saga of engine nock solved and engine is back and running w/o any issues so far.

The KNOCK WAS THE WRIST PIN BUSHING.  Had to replace rod as too much material had to be honed off and would have had to get oversize bushing and then hone it out.  Got used rod and cap from Joe Cutler and machined rod and bearing cap then honed out to take 0.10 bearings.  Replaced wrist pin bushing and weighed new rod and matched weight of old rod assembly.  As said above engine is running and only a few hundred dollars was spent.  As you know this is a hobby and your labor about 10 cents an hour w/o overtime but the benefits outweigh the costs.

[CadillacRob]

Sorry to hear you went through that, glad to hear you had the skill to diagnose it.

Being that two people are experiencing issues with recently rebuilt 331's it makes you wonder if its chinese parts here.  Did you guys order rebuild kits off ebay?

[49 Convertible]

Not that I am aware of.  The pistons, pins and bushings came from Egge and I have all the faith in the world in them.  It must have been a defective wrist pin bushing from the start and since the engine runs /ran so well I pushed it to the limits at 75 to 85 mph coming back from the GN in Vegas, some 300 miles away.  Anyway  the issue is now fixed and I now know that a knock is not always a rod or crank bearing issue.

Engine sounds and runs like it should now.

[kav]

I actually reused my rods pistons and pins , as they were all fine , just rehoned ,reringed and all other new parts  . I am investigating the vacuum pump and have found a slight leak in the line , but will be also investigating a lifter . one lifter took a very long time to pump up on initial start up . I also have to do some adjustments on the gearbox /accelerator linkages .