I'm considering another project (yep, added to the six I already have on the drawing board!) I have a 1951 GMC 1/2 ton frame that's just begging me to turn it into a doodlebug tractor, along with a couple of crash box 4 speeds and a vacuum shift 2 speed rear axle. I've also got a few Mercruiser 4 cylinder boat engines, the same design as the Chevy II 4 banger from the early 1960's. 4 cylinder engines in general have a bunch of oddball harmonic vibrations that tend to unscrew bolts at certain engine speeds. I'm wondering if, and/or how much weight would need to be added to a flywheel or a harmonic balancer to dampen out those vibrations when a bellhousing, clutch, and transmission gets grafted onto a Mercruiser marine engine? I could probably run the original marine flywheel, and adapt the driveline to some type of remote clutch assembly, I suppose? Thanks in advance for any guidance! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I have a good friend that holds the world record for a stock block Model A powered LSR car and he is a strong believer in balanced 4 bangers. For street engines he first bolts and then tigs counter weights onto the regular Model A crankshaft. Stops nearly all the "shake the rear view mirror" harmonics. He has terminal prostrate cancer but if I can get his ear for a moment I'll see if I can pick up a few tips for you. A couple of his LSR engines for different classes:
Interesting! Since the Mercruiser engines run well in boats, I assume GM and/or Mercury has solved the balance problems. I'll probably go with the original flywheel, and do some adapting to put a manual clutch and pressure plate onto it. That will probably require spacing the bellhousing back a little to accommodate a friction disc for the clutch disc to engage. I've got a Model A engine that I'm thinking about adapting to some type of overhead cam 4 cylinder head and insert-type rod and main bearings. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Model A's are 200 CI (~3.3L). I ran a Model C 4 banger in my Model A pickup - higher compression, larger journals, and counterbalanced crank. Outran all the guys running stock Model A's. Model A's had a HUGE flywheel (maybe 40 lb), but I ran a cut down flywheel in my Model C engine. Also had a 4 cyl Dodge minivan that had a balance shaft in it. It was a POS.
Evan, that hotrodded Model A engine is barely recognizable as a Model A. The timing gear cover is the giveaway. Looks MEAN!
Last edited by klhansen; 08/29/20201:20 AM.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
I'm thinking about adapting an Olds Quad 4 DOHC cylinder head- - - -maybe converted to belt driven cams instead of chains! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Fundamentals of Automotive Engine Balance W. Thomson ISBN 13: 9780852984093
It has a lot of interesting information regarding engine balance. It is very difficult to locate for purchase (at least at a reasonable price) , but most libraries that have exchanges with local universities can usually get a copy on loan. (I have been looking to purchase it for awhile, but never stumbled across an affordable copy).
I read it several years ago, so I don't remember all of it in detail, but what I do remember prompts me to a ask a couple of questions:
I can see how flywheel mass could be used to help dampen torsional vibrations, but isn't there a second order vibration in four cylinder engines that is inherent to the design? As I recall it was caused by the difference in acceleration between the two pistons moving in the area near TDC vs. the two moving near BDC. Since the pistons travel a longer distance from TDC to 90 degrees than they do from 90 degrees to BDC, the acceleration rate is higher, generating unequal forces between the two pairs. In modern engines, this is compensated for by using balance shafts.
I can't speak for MerCruiser applications, but early on when a variant of that engine was used as the "Iron Duke", I seem to recall it got stroked quite a bit to keep the RPMs down. I think they also had pretty soft motor mounts in those days, and I also wonder if customer expectations with regards to NVH back then were not particularly high? Later in it life, I believe that it finally got balance shafts as well when they tried to spin it faster in order to get more HP out of it.
Does this sound right to all you engine gurus? Or, did someone slip crazy juice in my diet Dr. Pepper again?
Slipped my mind, we did a 1928 Chevy dump truck that had the firewall all cut out for a 216 six cylinder. Used a 55 up truck V8 bell housing, clutch, flywheel, starter on a 153 Mercruiser engine. Fit perfect and ran very smooth.
I've worked with some big 4 cylinder engines in farm tractors, both gasoline and Diesel models, and most of them have a balance shaft to set up an opposing harmonic to the destructive one that's been plaguing 4-bangers since T model days. There was a vibration-absorbing mount system sold for the older engines under the brand name "Float-A-Motor", but it simply masked the shake with some very squishy rubber cushions. It really did nothing to reduce the vibrations. My Dodge Ram 50 (Mitsubishi) pickup had a balance shaft, driven by something that closely resembled a piece of bicycle chain! I'll keep an eye out for that book- - - -it sounds like some interesting reading. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Tennant used that engine in their model 800 sweepers until 2012 it was outfitted for their application by a company named P.S.I. The flywheel used appears to be the same as a flywheel for a manual transmission. I will see if I can get a GM part # for it Monday.
Thanks! Since Evan was able to make his 4 cylinder swap work without a lot of special adapting, it looks like Mercruiser has figured out a way to internally balance their engines. I believe a Mercruiser 4 cylinder, plus a couple of 4 speeds and a 2-speed rear axle will come up with enough gears to make a Doodlebug climb trees- - - - -now to figure out how to get enough traction! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Model A's had a HUGE flywheel (maybe 40 lb), but I ran a cut down flywheel in my Model C engine.