Burtz vibrations

[sr325]

Hi Guy, I recently finished building my Burtz engine and it is not nearly as smooth as I had hoped. Ive got even compression at close to 90 lbs on all cylinders, I had the flywheel and clutch Balanced and the engine pulls strong and evenly through the rpms. Vibration is worst when engine braking. I understand that these engines can never be perfectly smooth. But how can I determine if it is vibrating worse than it should? Thanks for any thoughts.

[norcalal]

Check your motor mounts first!

[Lawrie]

Yes on the motor mounts,specially the rears , mine had cracked original engine mounts
Lawrie

[nkaminar]

I will also say to check the motor mounts.

[sr325]

Oh, forgot to mention, motor Mountain are all new float a motor front side and rear. They were loose on my first test ride but I quickly figured it out and tightened them up.

[Joe K]

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New clutch disk? It may get better as it "dusts off."

A higher compression engine can be "lumpy" in spin-down (braking), which may be causing momentary "slippage" on a new clutch.

Joe K

[Richard Knight]

You might want to search around on tightening the bolts on the floaters. Mike k has some interesting comments on un equal tightening which I agree with. Also tightening too much will cause transfer of vibration. Hopefully your balancer did a good job.

[Will N]

A 4 cylinder engine (without counter-rotating balance shafts) can NEVER run without vibration- even with a counterbalanced crank and with every rotating assembly balanced.

[nkaminar]

The tightening of the Float a Motor mounts is critical. Just tighten so that the bolts though the rubber pads are snug. Do not over tighten. The stock motor mounts in the front work better.

A lightened flywheel will produce more torsional vibration than the stock 65 pound flywheel.

[Jeff/Illinois]

I don't have an answer to your problems, sorry, and it looks like the possible concerns have already been addressed
But expanding upon the four cylinder cars can never be made to run smoothly--- it seems the modern cars have that down pretty good probably from crankshaft dampeners that Model A's didn't have... and I was always curious 'How the heck do they balance the new THREE cylinder engines And how does a four stroke engine work with three cylinders?

[Y-Blockhead]

Originally Posted by Jeff/Illinois

But expanding upon the four cylinder cars can never be made to run smoothly---

Unless it is a horizontally opposed 4 cylinder... AKA; Boxer, VW, Porsche, Subaru

[David in San Antonio]

Jeff/Illinois - A bit of DuckDuckGo rummaging suggests that a balance shaft has been used with great success in 3-cylinder four stroke engines. Interesting (to me, anyway) is that Lanchester (contemporary of Henry Ford) designed engines for their cars with balance shafts to quell vibrations. Flash forward to Porsche bumping the displacement of the four cylinder engine in the 944 in two steps to 3 liters (approx 201 cubic inches, just like our Model A engine) and was frustrated by their inability to tame the rocking couples of a big four. Ultimately they capitulated and licensed the system that Mitsubishi had patented for their 3 liter four cylinder engine utilizing dual counter-rotating balance shafts , one high in the block, the other low, which powered the Starion, (a rebadged version was also sold by Dodge? Plymouth? Some Chrysler label), as a competitor to the Datsun (Nissan) Z car, which used a straight six (inherent first and second moment balance) and the Mazda RX-7 which was the smoothest of all with its Wankel rotary. It didn’t vibrate much but had its own issues.
For what it’s worth, my relatively new “touring spec” A engine (counterbalanced crank, Burtz 6.5:1 head, and Burtz cam, but rebuilt A block, not Burtz block) is harsher, noisier, and shakes hard. The ammeter needle is a blur at idle. It is indeed much stronger, accelerates up long hills in third that used to require second gear, and accelerates from 30-55 mph with alacrity, a proces that had been glacially slow. It is not as sweet as before, though. Presuming the motor mounts are in good shape, it may be that we’re crowding the inherent design limitations of a long-stroke, large displacement four cylinder engine with no harmonic balancer by increasing the compression ratio 50% higher than original spec, compounded by a higher performance cam, both made possible by gasoline with double+ the octane rating available in 1928-31.
On the other hand, some Burtz engine users have not reported increased vibration.
Another Model A Mystery.

[Synchro909]

Vibrations on over run can be caused by a sloppy universal joint. Have you checked that?

[Lawrie]

My A had the some vib on overrun through using 3 engines, the last was the current Burtz eng,I took out the original box type rear mounts that were both cracked, I didn’t like the floats motor ones, so made my own using a V8 engine Mount, it’s now the smoothest it’s ever been.
Lawrie

[Richard Knight]

Lawrie, could you post pictures of your home made motor mounts? Thanks

[Phil Brown]

Originally Posted by Y-Blockhead

Unless it is a horizontally opposed 4 cylinder... AKA; Boxer, VW, Porsche, Subaru

And the VW and Porsche run without a harmonic balancer

[Lawrie]

Richard,
I will when I’m back home after the 15th,
Currently in NZ touring around after the national A rally there
Lawrie

[Terry Burtz, Calif]

Originally Posted by David in San Antonio

Jeff/Illinois - A bit of DuckDuckGo rummaging suggests that a balance shaft has been used with great success in 3-cylinder four stroke engines. Interesting (to me, anyway) is that Lanchester (contemporary of Henry Ford) designed engines for their cars with balance shafts to quell vibrations. Flash forward to Porsche bumping the displacement of the four cylinder engine in the 944 in two steps to 3 liters (approx 201 cubic inches, just like our Model A engine) and was frustrated by their inability to tame the rocking couples of a big four. Ultimately they capitulated and licensed the system that Mitsubishi had patented for their 3 liter four cylinder engine utilizing dual counter-rotating balance shafts , one high in the block, the other low, which powered the Starion, (a rebadged version was also sold by Dodge? Plymouth? Some Chrysler label), as a competitor to the Datsun (Nissan) Z car, which used a straight six (inherent first and second moment balance) and the Mazda RX-7 which was the smoothest of all with its Wankel rotary. It didn’t vibrate much but had its own issues.
For what it’s worth, my relatively new “touring spec” A engine (counterbalanced crank, Burtz 6.5:1 head, and Burtz cam, but rebuilt A block, not Burtz block) is harsher, noisier, and shakes hard. The ammeter needle is a blur at idle. It is indeed much stronger, accelerates up long hills in third that used to require second gear, and accelerates from 30-55 mph with alacrity, a proces that had been glacially slow. It is not as sweet as before, though. Presuming the motor mounts are in good shape, it may be that we’re crowding the inherent design limitations of a long-stroke, large displacement four cylinder engine with no harmonic balancer by increasing the compression ratio 50% higher than original spec, compounded by a higher performance cam, both made possible by gasoline with double+ the octane rating available in 1928-31.
On the other hand, some Burtz engine users have not reported increased vibration.
Another Model A Mystery.

Balance shafts are for the comfort of drivers and passengers. They do nothing to reduce stresses in an engine.

If a racer decides to race a modern 4-cylinder inline engine, one of the first things to do is remove the balance shafts to save weight and increase horsepower.

[Keith True]

John Deere used dual balancer shfts in a lot of engines.Right at the bottom of the blocks,almost oil pan rail level.I replaced quite a few of them.They had bushings,like cam bearings,and there was a tool to press a little dimple in them that would keep them from walking out of the block.I don't remember how they were oiled,but all the repairs I did on them were from running dry.I still have the timing tools used to set up the shafts in the engine.

[Y-Blockhead]

Originally Posted by Terry Burtz, Calif

Balance shafts are for the comfort of drivers and passengers. They do nothing to reduce stresses in an engine.

If a racer decides to race a modern 4-cylinder inline engine, one of the first things to do is remove the balance shafts to save weight and increase horsepower.

I once raced motorcyles in the California Desert. I had a 504cc single cylinder KTM. It had a balance shaft that we removed for this reason. It didn't do much good in the first place... how can you expect a 504cc single not to vibrate.