Hi guys. I have a 26 Roadster and I had the engine rebuilt several years ago with a scat crank, insert bearings, H beam rods, new pistons, 280 strip cam, metal timing gears, nh carb, distributor. I also had the trans gone through at the same time and balanced. I drive it often. It starts right up and runs great BUT it has always had this annoying vibration at higher rpm range. It seems to be consistent with engine rpm not the speed of the car. It happens in low just before I shift and in high at about 35 mph. It also happens in low ruxtal at the same rpm. Is there something I should be looking at, maybe a belt pulley. I pulled the belt off and no difference so I figured I eliminated the fan and belt as possibilities. Any suggestions? Thanks.
Could be a loose or worn front motor mount. You can check it by lifting the hand crank just enough to take away any slack between the hand crank and the hand crank bushing. Once there carefully jerk upward on the crank. If you feel movement then it's either worn or loose. If loose you may need to tighten the bolts, shim it, remove some material from the cap depending on the situation. Just a guess but worth checking.
35 in low pedal?
Scott doesn't say he does 35 in low pedal!
It is still an antique engine. No harmonic balancer, four cylinder no offset firing. Even with a new counter balanced crankshaft, it is pretty tough to make them vibration free. Although some of the Montana 500 crowd get awfully close (and THEY have to use a stock crankshaft!!!). You might want to have some other model T people compare your car to theirs? What you are noticing might be about as good as they usually get.
Back in the days when we had real gasoline, and average model T people tended to drive a little faster than most do today (I generally try to stay out of discussions about how fast is TOO fast)? Most T owners noticed a vibration at about that speed which smoothed out at just about another hundred or so rpm.
Scott, I have the crank, flywheel, and triple gears spun balanced together and that takes care of it. I years ago static balanced my engine then took it to be spun balanced and they drilled four 3/4 inch holes in different locations than I had to balance it. It now runs 50 with no vibrations. Years ago a friend Bud from Michigan asked if I could get his dynamically balanced found a place and 100. later it was smooth. Had one that had the Dunn counter weights on it, would rattle your teeth out, had it balanced, still rattled, took the weights off and rebalanced and it ran smooth?? Hope this helps. Joe
Do you have the wood blocks & side bolts in your rear engine mounts? If not, try that.
Thank you Joe! This morning i find i need to let my hat out 2 notches before i put it on.My Model T also thanks you! Today people use a Scat counter ballanced crankshaft but sometimes hang that huge flywheel assembly with no additional ballance?? Rebuilds can be very expensive so why not spring for a little more to protect your engine? At 100 plus years you can't usually drag a perfect engine from a fence row free!! Joe is the real man in this story and i only spread what [often too thick] little i have learned.Again i say thank you Joe!! Bud.
I do not have wood blocks or side bolts in the rear engine mount. I will do some research to see what I need and I will check the front mount also. Start with the easy stuff. Thanks for all the help.
Those wood blocks would help. Also do a compression check. You could have low compression on one cylinder which would cause a harmonic vibration at a certain speed. The faster and more open throttle puts more strain on each cylinder as you drive. If one is low, you would have something similar to a misfire on one cylinder.
A little bit about balancing. This from my engineering experience balancing gas turbine engines and motor cycles.
First make sure all the pistons with pins and rings and rods weigh the same. Weigh the rods at the small end and large end while the rod is horizontal.
Do a dynamic balance (spin balance) of a crankshaft with counter weights (like Scat crank). Machine cylindrical weights to bolt onto the rod journals that are about 70% of the weight of the piston, piston pin, rings, and the weight of the small end of the rods including pin bolt plus 100% of the weight of the large end of the rods. Why? Because at top dead center and bottom dead center the pistons etc. are reversing and must be counter balanced but at the 90 degree points only the large end of the rod needs to be counter balanced. This is a compromise because, with exception, no piston engine can be completely balanced.
Then balance everything else. Mike Bender has a nice video on how to balance the transmission parts.
Put everything together and don't bother to balance the assembly. I have seen the balancing undone because the operator of the dynamic balancing machine did not know how to do the setup properly when balancing a complete turbine assembly. If you have complete confidence in the operator then you can balance the assembly but my personal belief is that it is not necessary as born out by my experience with gas turbines.
Scott, I wouldn't know what to do if any one of the 1/2 dozen T's I have had or still have if there was not a vibration or rattle. Without a speedometer, how do you know your speed? Don't tell me you are one of those "phone people" that drive and look at their phones!! I know by a certain vibration that I am going approximately 25 and a certain rattle that comes in around 30 and after 35 "I rattle". Henry's system is not wrong most of the time.
R.S. No. No I donít Watch my phone to see how fast Iím going 😂. I use the seat of my pants method, and my wife had paced me in her car. I thought with all the crap I put in my engine it would be a lot smoother. I enjoy the character of my T I just donít want it to fly apart.
I placed 1/4 inch thick rubber sheets under the rear motor mounts. This made the car much smoother to ride in, but obviously is not fixing any balance issues.
Yep. Considered that too.