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Engine mounts - vibration


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Finally narrowed in on the engine mounts. Someone had run bolts thru the rear mounts to hold the two halves together. With the bolts removed the engine now rocks slightly when the engine is reved. All I can say is it's terrible the price to replace and rebuild all of the engine trans mounts.

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Has the engine been apart recently? Did the vibration just start or has it been there for a while? If it just started, look at the harmonic balancer, and if the shake has been there since you owned it, check to make sure the flywheel is properly istalled

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I don't know how long this has been a problem, as I just got the car. As I fix things I observe other stuff. I first concentrated on getting the brakes working , so I could move it around the yard without crashing into the house tongue.gif

Long and short of it, could be new could be an old problem.

My understanding is that the head was off, but that was it, and a new clutch.

The harmonic balancer ...what should I be looking for/observing there?

thanks

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I've pulled the cover and with the use of a dial gauge found that the flywheel has 19thou of "runout" (not sure if that is correct term). That can't be good?

What all does one have to do to remove the clutch/flywheel assembly? (i've ordered a service manual but it will be a couple weeks before it arrives frown.gif )

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Good Morning: The first thing you want to check are the engine mounts, both front and rear. The rubber rots and cracks. Believe it or not the engine can actually move around. This last summer a friend in the local AACA club had this problem with a car and the engine would move forward to the point that the fan blades were making a ticking sound against the radiator frame. This movement puts stress on the drive train, especially in a Buick, because of the torque tube which gives the system rigidity and strength. The whole system is bolted together with very little flex. Yet, it must be properly lined up for many purposes. If out of line there can be shaking. Next, I would be sure to check to see each cylinder is firing and getting gas. A miss in the engine will make the engine shake and vibrate. Analyzing this also involves a complete examination of the electrical sysem. For example, a tiny crack in the distributor cap can cause a miss or a crack in a plug wire can cause a spark to jump to metal and make the cylinder miss. We have all excluded one or more potential causes only to come back to find what we thought was not the problem was. In addition, when you start taking the mechanical components apart and reassemble you will have the same problem if electrical, gas or air is the problem. Pulling the fly wheel is a major task which I have done many times. It involves swinging the entire rear end away from the transmission, removing the transmission and clutch assembly. Next you unbolt the fly wheel and will find it cannot be removed from the bell housing without removing the rear main cap (inside the oil pan) and bottom half of the bearing. Why Buick did not build the cars so the fly wheel could be removed without removing the rear main must have been an engineering problem. In any event it is a major task. Also, be very sure you mark the fly wheel and the rear hub of the crank shaft with a sharp punch as the fly wheel will go on six or eight ways and only one is right with the timing of the car. I could not recommend taking the drive train apart until ABSOLUTELY excluding all other systems as the problem. Eventually you will unravel this problem and will probably find it is a problem much more simple to fix than a mechanical problem. Post your eventual findings on this web site and good luck. Patrick W. Brooks

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Today I spent some time and reset the valve tappet clearance. found one that was very loose and a couple that were tighter than the rest.

Went for a short run after that and felt that it is running smoother than before, but still not a smooth as it should. (at least I expect these engines run smooth as silk when everything is right - true or false?)

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The list of things to check when I get it torn apart is growing. One of those items that should be replaced and often overlooked.

Now if only the trans gasket set and service manual I ordered would arrive.

Anything else I should replace while I've got it all apart?

How difficult is the engine rear main seal to replace? - only fluid leak on the whole engine.

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Replacing the rear main seal is not possible without taking the engine apart. You say that the engine is leaking everywhere. I would first clean the engine completely, then drive it for some time to see where the oil comes from. Sometimes the oil is coming from a spot at the front of the engine and blown al over by the fan. If that is not the case look further. I guess see oilleakage at the oilpan, oillines, valvecover and so? Most of these places can easely be solved, mostly gaskets that can be renewed without extensive disasseblies or joints that can simply be tightened. I do wonder if the oil is old or too thin? Or is the engine perhaps building up pressure due to a clogged or closed cranckcase vent?

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OK, I agree, that is a possible way to read it too and less work. English is not my native language so sometimes I make a mistake. Talking about that (only smirk.gif)oilleak: I wonder if the problem is the rear main seal or too much play in the bearing? Maybe it is an idea to remove the oilpan and the bearingcap and measure the play with plastigage. I don't have the limits for the 1938 but on the 1931 the play should not exceed 0,002 inch.

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Just completed an overhaul of the carburetor, so now to investigate the vibration further.

I will be pulling the trans. anyway to replace the leaky gaskets in it. So that will give me opportinuty to check out the clutch, and pilot bearing (kind hope that is the source of the problem - cheap to fix if it is). And have a look at the rear main as well, I was planning to drop the oil pan and see what surprizes it may hold ...expecting lots of sediment.

When I had the engine running today I tried to judge if there was a difference in the amount of vibration with clutch engaged and released. My feeling was that it was less with clutch disengaged.

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If that is the case it indicates that the vibration is caused by the primary shaft, so the problem is in the clutch/pressureplategroup or pilot bearing. The question is if the vibration that remains with the clutch disengaged is normal or not. Have you asked anyone familiar with Buicks of that age what his (or her) opinion is? Allthough it is a straight eight that is very smooth by nature there is allways some enginevibration. That vibration will be more noticable if the rubbers of the enginemountings are old.

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  • 2 weeks later...

update

The pilot bushing was worn, but this is not the source of vibration. Contributing factor likely.

After completely removing the clutch and running with the bare flywheel the problem persisted. A measurement of the clutch surface on the flywheel indicated runout as was noted at the beginning. after a bunch of shimming to get it running flat the vibration has decreased greatly. Only a narrow band of rpm that is rougher than the rest.

I'm attaching a pic of the rear motor mount. My question is do they normally have bolts running thru holding it all together?

Edward

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So you dismantled it. A lot of work but the only way to find out. You talk about a "runout surface". Is the runout in an axial (in the line of the crankshaft) or radial (up and down) direction? I don't know which runout you mean, but how did you correct the runout with shims? If it is an axial runout and you put shims between the crankshaftflange and the flywheel you could get a lot of stress on the flange with the flange likely to crack.

From the picture you can clearly see that the rubber in the motormounts is very bad. That gives a lot of vibration in the car! I really should renew that. The mounting seems to differ from the 1931 mounting but the principle will be the same: no metallic contact between the engine and the frame by using two rubber sheets. With this mounting the part that is connected to the flywheelhouse squeezes two rubber sheets on both sides of the part that is connected rigidly to the frame. I can only see one sheet, the other one should be on the other side of the framemounting. Maybe that one is missing. The bolts go all the way through but these should be kept on a distance with a spacerbushing so there is no metallic contact between the the engine and the frame.

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I looked for you at the site of Bob's Automobilia and they sell motormounts for the 1938. The link is: http://www.bobsautomobilia.com/cgi-bin/shop.pl/SID=1136470716.29890/page=product.html/product=79 at US$ 149 each.

It appears to be a vulcanized rubber and not rubber sheets, so there is a greater difference between the 31 and 38 then I though. Never mind: you can get new ones.

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Interesting discussion!

I have a '38 Special that also exhibits some degree of vibration. In my case the engine is smooth up to about 2500 to 2800 rpm (about 45-50 mph), then it seemes to vibrate. You can reproduce this in the driveway, clutch engaged or disengaged. One thing I always wrestle with is - how smooth were these engines? For most of my driving it is fine, but if something is wrong, I would like to fix it.

My "restoration" has been a low budget job over the past 15 years. I am sure some things were done incorrectly over that time, as I did everything myself, learning as I went. The best advice (and most fun) came from working on the car with a great old friend who was a mechanic in a local Buick dealership from the 30's to the 50's. He cut his teeth on Model T's and A's at a Ford dealership, moved on to Buick, then serviced B24 engines for the army in WW2. He was always amazed at the high cost of parts, so some of my fixes were "homemade". For example, we rebuilt my mounts with rubber from a local supplier - could they be too stiff? too soft? Don't know.

Things I have done - ignition (check your mechanical and vacuum advance)

carb - mine is not quite correct, its from a '46, I believe.

clutch and pressure plate - balanced.

flywheel - (yes, you can install incorrectly, I can no longer see my timing marks!!!!)

Things that still may be wrong - homemade mounts, harmonic balancer, replaced only one bad piston when I had the engine apart. Or, maybe my incorrect carb leans out the mixture when at higher rpms. Or, maybe this is as good as it was??

Right now my focus is on re-building a spare transmission. When I swap the trannys, I will put the flywheel back in the correct orientation. Any leads on N.O.S. clutch gear, counter gear, and high speed synchro?

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Hello, it sounds to me if the vibration gets better by correcting the runout problem you might have some success by adding washers of various weights and at different places on the clutch-flywheel assy. I once had a v-6 GMC gas engine that would vibrate at about 60 MPH, it was bothersome and I started to experiment with different washers and got that puppy so smooth that it no longer was an issue. When you add weight to one place on the flywheel it will either get noticeably worse or start to get better. If you mark the starting place you can keep moving the weight around till you find that "sweet spot". This method also works quite well on ceiling fans in our houses too! Good luck! Buford 8.

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