Just took the Model A down for gas and the engine developed a strong low vibration about 2 miles from the house. It seemed to be running and shifting fine, and had good oil pressure. I checked the simple stuff; mufflers aren't rubbing on the frame, same in gear and out of gear, and all eight plugs are getting spark (haven’t checked to see if they are all firing). There isn't any noise to speak of. You can hardly notice it standing next to the car, but there's a scary deep vibration coming up through the floorboards with the engine running whether the car is parked or moving. I was afraid to bring the engine over a fast idle so I don't know how rpm dependant it is. I've put about 800 miles on the motor since I put it together and it has always run great. It's a high mileage 8BA short block that had about 110 psi compression across the cylinders. Hot oil pressure is 15 pounds at idle and 30 psi at 2500 rpm (about double those numbers when cold). I didn't plasti-gage the bearings but I didn't see any heavy wear when I checked them. The engine was pretty clean, so I lapped the valves and put her together. Here's the specs (all new or rebuilt): Standard Mellings pump Isky Max 1 cam Aluminum timing gear Adjustable lifters, Lincoln valve springs and split guides Harman Collins dual coil crab distributor, points plugs wires, cap condensors and coils Center dump Edelbrock heads Edelbrock Super Dual intake and a pair of 94's Red’s headers and rear exit Smitty’s 2-brush Generator Sealed bearing water pumps Typical Tardel frame mounts and doughnut bushings 32 K member and tranny mounts I’m running a closed drive 39 3-speed that I went through with new bearings and synchros. The flywheel was resurfaced and it’s got a rebuilt 11” Detroit Clutch clutch, pressure plate and pilot/throw out bearings. The starter is rebuilt but seemed to be hanging up every once in awhile. The only thing I did since I ran the car last was put on a starter bracket to the oil pan to see if it that might fix it. Could a sticking starter be causing this? I'm thinking the next thing to do is remove the drive belt to eliminate the water pumps, fan idler and generator. Any ideas?
You might stay away from the 2 mile mark down the road....? You might also take an ohms reading from your plug wires..
Go all around the motor at hot idle with your long screw driver to your ear and listen at the water pumps, and along the bottom end. Then the valve system could have a sticker, fixed with Marvel oil or similar product. Are you sure you torqued all the rod nuts? They are a bitch to get at sometimes. good luck!
Lots of good suggestions. I've been fooling with cars for about 30 years and have never had a problem like this. Very odd how it came up so suddenly. Need to rule out the easy stuff first. It's no problem to check the resistance of the plug wires. I should probably take a look in the dark while the engine is running to make sure one isn't arcing. The motor mounts look fine, but I will jack the engine a side at a time to make sure they are tight. Tranny level is easy to check, so that will be next on the list. I keep the car inside and didn't notice any puddles. Am wondering if you can grease the throwout bearing through the inspection hole on the top of the trans. I doubt I'll be able to get much of a look at the flywheel through it, so I'll have to drop the starter plate to make sure the flywheel isn't loose. I've never been good with tracking down noises with a screwdriver. It would probably be just as easy for me to drop the oil pan to take a look at the bottom end and check the compression to make sure the valves are doing their thing. The whole valvetrain was out when I lapped the valves. I won't be able to work on this til Saturday, but keep the ideas coming.
you can grease the throwout bearing thru the inspection plate.Does it still vibrate when the rod is standing still or do you have to be moving.
What drive shaft are you running? Has this been modified? Is the universal joint in good condition? If you are running a solid driveshaft with the centre bearing it can cause vibrations. Do you drive out of the vibration as speed increases. Is it on accelerate only?
The vibration is there anytime the engine is running, parked or standing still. The vibration is there with or without the clutch engaged. I was afraid to rev over a fast idle in second, enough to limp home, so I don't know how rpm dependant it is. The driveshaft is stock Model A with V8 u-joint. It has not been modified. There is no center bearing.
The reason I suggested loose flywheel is that I believe the 8BA flywheels are different than the 59AB flywheels and they don't bolt up the same on the crank. (Correct me someone if this is incorrect)
check the fan for worn bearings. also it may be nothing, but that pump should make closr to 60 lbs at speed,
Two preliminaries...remove belts, peer in through clutch inspection cover with it running. You can see a lot there with a strong flashlight, though I suspect the clutch test suggests nothing wrong in that area. If it comes to that, at least pan should be easy to drop with your combo...I think what you have done so far pretty well rules out drivetrain, almost rules out flywheel and clutch.
I had a similar problem with the 8BA in my F1 when I first got it. The motor was freash but it had a strange miss and vibration, It turned out that a couple of valves (actually all most all of them at one time or the other) were gauled and hanging up off and on. The solution was to use valves with chrome plated stems. Here's hoping your problem is just an ignition miss.
That's a good thought about the crank pulley, Keeffer. I'll check that before I even fire up the engine when I remove the belt. The pump puts out about 60 pounds at highway speed (~2500 rpm) when cold. Always heard the rule of thumb is 10psi/thousand RPM and that pressure isn't critical for a flathead. I wasn't thinking it was a problem and just mentioned it to verify I that had pressure. With as deep and powerful as the vibration is, I'm thinking something heavy is seriously out of balance. I can't imagine what since the engine idles smooth and doesn't make any odd noises.
The thought of heavy imbalance with engine still running smoothly seems to point at flywheel/clutch...but I'd expect something noticeable to happen when stepping on clutch then. Pop that cover and stare in there, and have someone to work the clutch while you look. Since it is there at rest, I think everything abaft that is innocent.
Many years ago I got the same symtoms with a busted center main cap. Funny part was ,went to wrecking yard kicked over a flattie ,pulled pan and grabed a cap. Fit my block perfect plasti gaged fine. Ran it many many miles afterward no prob. No line boreing needed. From what I have found over the years in the parts biz some makers/engines main cap were made to be service replaceable without any further machining. Good luck.
That's a good thought on the busted center main, John. I was just wondering if there might be water leaking into a cylinder and the engine is partially hydro-locking?
Commonest cause of busted center is those strap type reinforcements with the bolt in center...caps are all very close. Often you get direct fit, usually trying a couple will get you right in spec with no need for line bore. Really good original machining. Hope it's something simple. And do runnit without belts to get rid of all suspects up front.
Well if all else fails check the flywheel itself. I notice you said it was resurfaced. Did you lighten it at the same time? I had a similar problem with a lightened flywheel that was not rebalanced. Rebalancing made all the difference in the world. Also, one other thing comes to mind. Was your clutch new or used? I've had one get "wonky" on me causing vibration. The springs were out of tension and it tried to partially engage. You are not experiencing other symptoms of that. So likely not your problem but with all the other suggestions...Who knows? Good luck -Mike
Check the main caps.I had a good running 8ba with a vibraton. Center cap fell into oil pan and the crankshaft broke in half at an angel still made it home from 25 miles out.If I had just pulled the pan and retorked the caps would have saved myself a lot of work.The rear cap was craked too when i pulled it.It ran ouer a year with the vibraton whitch kept getting stronger.If I had just pulled the pan.
I didn't have any weight removed from the flywheel, just had the machine shop resurface the clutch disk face. Since it was the flywheel that came with the engine, I didn't have it rebalanced. The good news is I just found at least one problem- I checked the motor mount nuts and they were tight. After a couple of you had mentioned a possible cracked main cap, I remembered that when I originally tore the motor down, the front and middle caps were switched. I had put them back in their correct locations, but started wondering if swapping the caps to their correct locations hadn't put a weird load on one of them and caused it to crack. I decided to take a look at the bottom end first instead of removing the V-belt. I didn't want to risk starting the engine again until I was sure I wasn't going to blow out the short block, and it was hard to imagine that kind of a deep vibration was coming from the pumps, generator or idler. I dropped the pan and everything looked ok. What a relief. Checked the torque on the mains while I was in there and they were all fine. I pulled the spark plugs next. They looked fine and no water shot out of the holes when I cranked the motor over. Another relief. Figured it must be in the bellhouse so I dropped the starter plate to take a look. I was trying to turn the motor over by hand to see the top side of the flywheel when I noticed that the bottom RH motor mount donut wasn't in contact with the frame mount. Hummm. Turns out the holes in the washers that came with the mount kit were too small to fit over the shanks of the through bolts. The mount nuts drew up tight, but were drawing up against the washers instead of actually clamping the frame mounts. I took out the washers, torqued the mounts, and put back the plugs & starter plate. I had torn the gasket taking down the pan, so I'll have to get one from NAPA before I can see if that fixed the vibration. Will post an update as soon as I get the pan on.
Try to find a set of old mounts to provide the washers and cups, and make sure the rubber is pretty firm. Some of the repro sets have absolute crap hardware, and some have rubber that's like jello!
Well, the motor mounts didn't fix the problem and I didn't see anything wrong in the bottom end when I had the pan down. I'll take off the front drive belt and check inside the bellhouse when I get home form the doctor's this afternoon.
I found the problem. The screw-in pot metal retainer for the front bearing of the 3-brush generator I converted into an idler pulley was cracked. When I removed the fan to take the load off the idler, the vibration pretty much went away. It's the 32-36 style that loads from the front with the wire C-clip, retainer, felt washers and opposed taper bearings. Bruce did a tech post on how to disassemble the bearing assembly: http://www.jalopyjournal.com/forum/...8&highlight=flathead+generator+bearing+remove I was told by a generator man that you can replace the finicky old tapered bearings with a pair of NSK 6202DU sealed bearings, so I gave them a try when I put in the new retainer and rear bushing. They fit like they were made to go there and you don't need to fiddle with setting the clearance. Just leave out felts/washers and snug up the bearings with the retainer. I can't believe the difference the new retainer and bearings made. No more scary wobble or vibration
A long time ago I had a busted center main cap problem like John Evans. I found an old CM cap, installed it and it required no line boring. Mine was cracked in three places and when it was loosened up, fell apart. But when the engine was running with the bad cap it made a hellacious grinding sound in addition to the vibration.
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