I partially rebuilt the engine in my 27 about five years ago. Rebore, new pistons, adj. valve lifters, new rods, new timing gears. I don't put many miles on it, probably less than 500 since rebuild. Last year, I thought I could hear a rod knock so I took it apart to check. Bearings look good but was able to take one layer of one shim out of 2, 3 and 4 rods and 2 layers of shim out of #1. Everything else looks ok and crank pulley is tight. Still thinking I can hear a knock on "coast", not under power. Starting playing around and it seems that knock goes away if I retard spark a bit. However engine seems to run better with spark more advanced. I am running high test gas to avoid ethanol. Ignition system and carb (vaporizer) are stock. What's your opinion?
First question did you have the crank ground. If not that could explain why in 500 miles you are pulling shims. Out of round or taper makes it hard to fit rods and mains. IMO.
I shouldn't even "comment" after an engine builder like Mike Bender did, however, I'm sure that even Mike would agree that there are quite a few other possible reasons for something that sounds like a rod knock,.....timing gear, camshaft, heck, I was pretty worried about a knock that one of my"T's developed, and it turned out to be the crankshaft pulley pin working its way out to where it was "knocking" on the nose of the pan. Many possibilities,....FWIW,.....harold
Might be cam shaft end play. When you rebuilt the engine did you check front cam bearing to cam clearance. They sell a shim for that.
My buddy Clay says when you hear a noise you do not like, open the exhaust cut out. My solution is to take a corner a little too fast and my wife will make enough noise to cover it.
I just turn off my hearing aids.
Thanks to everyone for the suggestions;
Mike-No I didn't have the crank ground. I didn't have any rod noise before and just assumed (silly me) that it was ok. If I don't come up with anything else, I will mic the journals and see what I get.
Harold-Timing gears and gen gear are new, crank pulley pin is in place.
John-I don't think I checked cam end play. Can I do that in the car?
William-Sorry no cut out.
Neil-I don't usually wear my hearing aids when I drive the T. Too much clatter.
Harold is correct, lots of possibilities of a source for a knock.
What ran up a flag for me was the statement that in 500 miles we removed some shims.
Not having the crank ground, I would bet means we have taper and out of round. Not knowing how Dave fit the rods or measured the crank to see if it was within useable condition, I assume the rods wore in some to fit the crank, Babbitt moves.
After adjusting the rods, he thinks he can hear something.
My advice, run it and see what develops, only driven 500 miles. Now if you are like me and taken off on a 5,000-mile run I would dig into it but that involves and engine hoist.
Dave, My 27 with distributor too had the same noise it would go away at load and return at coast. retard spark, go away.
check rods all ok, Babbitt was fine. that was 2 years ago. at end if last year had some transmission problem, so we pulled the engine. I then was able to check the main rods, put plastic gauge on all the caps, find it WOULD not register at all. check Babbitt all ok. remove shims, aligned transmission to crank. Noise was gone. Drive car 480 miles on tour this June. No noise car run like a top.
I would suspect that the rod bearings were not properly fitted when the babbit was re-poured. There were high spots which wore down very quickly and a few shims would be removed. Then more high spots wore down and the bearings were loose again. Maybe now the high spots have finally worn off and the bearings will stay in adjustment.
This is one of those situations where Plastigauge can be your friend...any taper will show up when compared to the chart on the package.
Hi guys. Thanks for the continuing interest. The rods were exchange units from one of the major suppliers. I initially fit them using plastigauge and that seemed to go well. The adjustment done a couple of weeks ago, I just removed enough shims that the crank wasn't hard to turn with plugs removed. This did not result in any change in the noise. Probably I should give it another try using platigauage to confirm the proper .002 clearance. What is the significance, if any, of the fact that the noise goes away when I retard timing a couple of notches?
Dave, plastiguage is only useful if the journals are round. Can you measure the journals in car?
I had similar noise on 2 engines after a couple of thousand miles. In both cases the wrist pins had tightened up in a couple of the ally pistons and the piston was slapping against the bore.
.002 is a little loose! It's about the maximum it will run without a knock. When you adjust it again aim for .015. It might drag just a little when you crank, but you should be able to turn it. After it has run for a few seconds it should turn easily on crank.