Miss at 40 mph

[greenacres36]

I just rebuilt the engine in my 1915 runabout. It has a slight miss starting at almost exactly 40 mph. Up until that speed it runs perfectly. I am using a roller Tiger timer. Does anyone think that may be the problem? I’ve heard of roller bounce. Does that seem like a reasonable explanation?

Adjusting the carburetor doesn’t seem to do anything and I don’t think it’s a fuel starvation problem because it pulls hills very well.

Thanks

[Jerry VanOoteghem]

Being a fresh rebuild, I would wonder if a valve isn't beginning to stick as it heats up at higher speeds.

Besides, I would NOT be running a freshly rebuilt engine up 40 mph.

[greenacres36]

I thought about valve adjustment. Probably got about 100 miles on it. I like to cruise along about 30 mile an hour is my favorite speed. I put about everything in it except for the block new. Scat crank and all. Just trying to give it some brief pulls and then back down.

[TXGOAT2]

I'd look carefully at the timer, or replace it, and look carefully at the wiring between the coils and the timer. I'd want to put on at least 20 hours of run time at various speeds up to 30-35 mph and avoiding hard pulls before running the engine fast and hard. Check the plugs for indications of oil fouling. Rings may not be fully seated. Retorque the head, avoiding overtorquing.

[speedytinc]

From what i have seen, new roller timers need work right out of the box. Contacts must be perfectly smooth. No gaps or hi spots.

[CraneJon]

90% of fuel problems are electrical.

I recently had a 40 mph miss in my model A. After checking fuel flows, ferrule into the carburetor, filter in the tank I read the above and checked the distributor. Carbon arc..new cap, top and rotor and no more miss!

I would look at your timer and coilbox
Jon

[Scott_Conger]

A scant 4 months ago you stated that you were new to T's and just bought this car. Now you're driving it at 40 MPH with a clear intent (to me at least) to exceed that speed once the "miss" is rectified. I am going to bet that you have not yet had a serious scare, like a child wandering out into the street in front of you, or a car backing out of a driveway that would put the fear of G-D into you at 25 MPH much less 40 MPH. Myself, I would be breaking in the engine at a far more sedate speed and enjoy the car for what it is...an enjoyable, 106 year old vehicle that is hazardous to drive in modern traffic at 25 MPH and downright dangerous at 40+MPH. I own 4 of them and have driven many thousands of miles, fully cognizant of the risks involved, and drive in a manner to minimize both the risks and the potential consequences those risks bring.

You just haven't seen enough "T" wrecks yet, much less a fatal one.

Take it easy and savor life at 28 MPH.

[Roz]

And we wonder why folks new to the hobby are hesitant to post on this forum. His car, his engine, his consequences. I've built quite a few Model T engines. A pull up to 40 won't hurt a new engine if you back off right away. Up and down helps seat the rings. Just my opinion, and why I don't share much.

[Rich Bingham]

Sage advice, Scott Conger, that should be seriously taken to heart! Sadly, it will likely be generally dismissed. For some time, the general consensus on these boards has been mostly supportive of notions that the venerable Model T is something that requires to be updated, enhanced, modified and re-engineered to compensate for the modern owner's total disbelief that automobiles of that era were neither capable of speeds much over 30mph, nor would the roads of the time permit it. The current crop of Model T owners seldom, if ever, drive on dirt roads, nor do they conceive of traveling at less than Interstate speeds Many are oblivious of the fact that first and foremost, a Model T was actually made to be a very capable all-terrain vehicle, not a high speed freeway cruiser.

[babychadwick]

I see many that seek to "improve" their T by making it say with brakes, seatbelts, etc. The biggest improvement to a T is not in equipment but in experience driving. By the time I had logged 500 miles in a T I had experienced the learning curve few experience. My first endurance run was a freshly rebuilt engine (of course 40mph was exceeded) over massive rough terrain. There were those stating as a new driver I shouldnt be allowed to run. I did come in to lunch stop needing a fair number of repairs with a new car. The point is you don't discourage new people to the hobby but listen and offer assistance when they ask without telling them what they must do.

[DHort]

Brian,

If you are new to the hobby listen to what Scott has to say. He is a well respected member of the T community, with many years of experience.

[Wayne Sheldon]

I would wonder about the valves, stems, and guides, including the lifters. How new is new, and how tight is new, and how strong are the springs? A common problem with fresh model T engines is that the springs are a bit weak (stronger springs might be a mistake!), and if the stems and guides are a bit too tight? The valves will have an rpm where the drag on the stems slows down the valve's return enough that the valves begin to 'float'. Not having closed completely in time for the intake (and sometimes even into the power stroke!) stroke causes a considerable miss at high speeds. Usually, as long as the valve floating isn't severe enough to cause trouble at lower speeds? After a few hundred miles the stems and guides will loosen up enough to stop causing problems.

Why not use stronger springs? Because the model T cam due to its size and profile doesn't like to push against stronger springs.

[greenacres36]

Maybe I am being misunderstood. I don’t plan on driving this car at that speed on a regular basis. I have rebuilt many engines in my time and the only purpose for letting her rip a little bit is to seat the rings. Also, this is not my only model T. I’ve had a model T before this car. I grew up farming as a young man and I am pretty capable with equipment. Model T is no different than a lot of other old farm equipment that we used to farm with. This has been a great experience for me. I’ve been a machinist for over 30 years but this was a new one for me. I learned to pour my own babbitt. I learned how to line bore the main bearings. I learned how to fit the crankshaft. And so forth. I bought a portable home and honed my own cylinders to the next oversize. I am proud to say that all of the cylinders were within .0002 of one another. I’ve done some challenging things in my life but I’m proud of this one. When I say new engine I mean probably 100 miles or so. I appreciate all the support that I get from this board and respect many of the people in the hobby. If anyone thinks that I have a death wish behind the wheel of the car I have a little bit more to live for than just going fast and dying behind the wheel of a model T. I also have a concern that if it is having a little bit of a misfire at 40 mph sometimes these issues become 35 mile an hour, then 30 mile an hour and so on.

[Scott_Conger]

Brian

your talents and ambition have likely served you well in life and will serve you well in the hobby as is evidenced by your doing ALL of your own work on your engine. Thinking over night on this, I'll mention that with a roller timer, it is most important to have the timer cover truly centered over the cam and they do not typically want to be centered naturally, requiring force and tooling to accomplish it. At least temporarily, you may wish to try a modern timer or a face-contact timer such as a New-Day timer which will not bounce if the cover is off-center some.

With respect to speed, for yourself as the Poster to whom I was speaking, and to others who believe I am "trying to tell someone what to do", I think that another careful reading of my earlier posts were cautionary and not accusatory or dictatorial. Oddly, some of the same folks who profess that they will drive as they please (please do!), are often the same ones who have ogled and speculated over pictures of recent "T" wrecks and immediately suggest that the only way to be safe in a "T" is to have disk brakes, seat belts, reinforced wishbones, etc.

My only point is that when anyone is new in the hobby, their tendency (as mine was) is to go faster or TRY to go faster than the car was designed to safely go. It's clear now that you are intelligent and prudent in this respect and are one of the few who probably did NOT need to be cautioned. That said, would any of the speed-proponents "I'll do as I damn well please" crowd (please do!) want to be driving 40+ and have this happen to them? https://mtfca.com/phpBB3/viewtopic.php? ... 97#p177697

The wheels on your car, at least as fit from the factory, are exactly the same as the wheel that failed for Russ

[greenacres36]

That wheel issue should be and is a very good cautionary experience for sure. I don’t take you post offensive by no means. I need to be careful and your guidance I much appreciated. Thank you.

With that out-of-the-way I have to admit I did not center the timing cover when I put the engine together. I knew better. However I don’t think I could have forced the timing cover to move much anyway. I was going to check it with a dial indicator when I had the engine on its head. I took the timer off today and it is most definitely the problem. It was a timer that I had bought on eBay. The contact pattern inside of the timer was not good and you could see evidence where the roller appears to have been bouncing across the contacts. There were lines. I put on another roller timer from a reputable vendor on the car today and it runs much better from idle to 35 mph. Funny how the silliest things can just bug the crap out of you. I do suspect my timing cover is out of alignment. I may have to go to a different type of timer. I have an I timer on my 26 and I really like it. The only issue I don’t care for is the inability to start the car on magneto if you want. My 15 will now.