Broken Exhaust Lifter and Tappet.

[Wilkit11]

Went for a ride yesterday and the JD was soon running on one cylinder. Both the tappet and the lifter were broken. What could cause a dual failure like this?

[Steve Swan]

I'm assuming these are factory parts? Where did they break? Can you post some pictures? If they are original 100 year old parts, it's within reason to suspect fatigue of at least one part that broke and then broke the other.

[Wilkit11]

Don’t know if factory parts or not. Here’s a pic.

[Jerry Wieland]

Don’t know if factory parts or not. Here’s a pic.

That is a puzzle. It does not look like fatique. Is the 'lifting pad' on the rocker smooth because in the lifting process the lifter has a little sideways movement because the roccker does not lift straight up but pivots on a radius? Jerry

[Wilkit11]

The lifting pad isn’t perfectly smooth and polished. I did find a slight, circular impression on the pad as if the tappet had been resting in one spot (see pic). The tappet broke where the treads are located. A third of the threaded area broke out. Thanks.

[Steve Swan]

This is the first time i have heard of a lifter arm breaking.

The lifter arm did break in the area where the pin for the roller goes through which would be the weakest area of the lifter. It makes me wonder if there was some sort of stress put on that area when the pin was peened.

I have seen tappets broken in the area of the thread portion of tappet. I can imagine as thin as this circumferential area is it could fatigue either from running over many hours of use or I'm wondering if the crack could be from over tightening the jam nut.

I'm trying to imagine a scenario where one part breaking caused the other part to break and I'm not coming up with any. I've seen much worse wear areas where the tappet strikes the lifter.

[aumick10]

Do you have a seized valve?

[Wilkit11]

Nope. Both the valve and the tappet move effortlessly in their respective guides.

I’ve been pondering this a lot . . . and I have come up with an idea that’d I appreciate your input. What if the exhaust valve spring was fatigued and allowed the valve to partially float? Still closing, but not as quickly as it should. If there was separation from the end of the valve stem and the lifter pad and they were only connecting when the valve was retracting as the lifter pad was rising . . . there would be a hammering effect on both. Over time and at higher rpm (I was running around 65 mph), this constant hammering could weaken both and cause a failure. That’s the best theory I have at this moment.

[Steve Swan]

Nope. Both the valve and the tappet move effortlessly in their respective guides.

I’ve been pondering this a lot . . . and I have come up with an idea that’d I appreciate your input. What if the exhaust valve spring was fatigued and allowed the valve to partially float? Still closing, but not as quickly as it should. If there was separation from the end of the valve stem and the lifter pad and they were only connecting when the valve was retracting as the lifter pad was rising . . . there would be a hammering effect on both. Over time and at higher rpm (I was running around 65 mph), this constant hammering could weaken both and cause a failure. That’s the best theory I have at this moment.

What year is your JD? What are your front and rear gearing ratios?

Looking at my '27 Rider's Hand Book, 74" solo machine, factory standard gearing ratios are, motor sprocket 16t, clutch sprocket 43t. Countershaft sprocket 28t, rear wheel sprocket 44t. These ratios are, according to the Hand Book, good for "ordinary service up to 40-45 miles per hour."

My firsthand experience with my restored '27 JD with factory ratios holds true to what the Hand Book describes. At 50 mph the engine has left its sweet spot and and at 55 mph the engine is revving out of my comfort zone. 40-45 mph is definitely the sweet spot with factory ratios; anything above 45 mph feels like the engine is beginning to rev more than it is designed for. Fwiw, my lower end is set up with a balance factor of 60%.

If you are running 65 mph with factory gearing ratios, I humbly suggest that the engine is over-revving which might explain the failures of your nearly 100 year old tappet and lifter arm.

For comparison, the current gearing ratios for my Frankenstein '27 are 18/43 and 28/44; the 18t engine sprocket gives me a sweet spot road speed of 55-60 mph. I did have "Frank" geared 18/43 and 28/41 with road speeds between 65-70 mph however these ratios made me shift from 2nd to High gear at no less 40 mph, preferably 45 mph. Following cars going the 40 mph speed limit in our mountainous ascents made me run in 2nd wishing to be in High gear.

[Wilkit11]

My bike is a 28 JD. Gearing is 18/42 then 28/44. Not sure how close that is to your gearing.

[Steve Swan]

My bike is a 28 JD. Gearing is 18/42 then 28/44. Not sure how close that is to your gearing.

You ratios are the same as on my Frank with exception to your clutch sprocket being one tooth less, which should give you a couple mph more than my sweet spot speed of 55-60, so 65 mph doesn't seem like you'd be pushing things... I am beginning to wonder if it was serendipitous that both parts happened to fail at the same time. You might contact Rob Nussbaum or Jon Neuman; both are active on JD Facebook as well as maybe other fellows on that site have had similar failures and others such as Jon and Rob have more experience than I do with and put a lot more miles on these machines than I have. 42t on the clutch sprocket seems a bit unusual, are you sure it's not 43t ?

[Wilkit11]

I’ve spoken to Jon . . . he’s scratching his head as well. Will contact Rob as well. You are correct, it’s 43 teeth on the clutch.

[Steve Swan]

I’ve spoken to Jon . . . he’s scratching his head as well. Will contact Rob as well. You are correct, it’s 43 teeth on the clutch.

So, you are running the same gearing ratios a i am. Frank only has 500 miles on a completely rebuilt engine, although i feel it loosening up. I've had the bike up to 70 mph, but much past 60 feels like i'm starting to push things... When i was running the 41t on rear wheel sprocket i could run 75 with more left on the throttle. 65 mph felt good; 70 mph felt like i was beginning to push things.

Keep us informed as to what you might learn. It would be nice if all the small moving parts in the engine could be replaced, one thing I'm always mindful of is those 100 year old parts still being up to the task of doing their job.

My Dad bought his '27 new back in April of 1927; he met a truck at an underpass where water had collected during a rain, the wash from the truck drenched him and cracked the front cylinder on his '27. By Dad's report, "I limped into the next town that happened to have a Harley dealer with the engine going pthh, pthh, pthh. The dealer took a cylinder of a machine in his showroom and got me back on the road again."

[knucklehead 61]

Steve, the ration on my 25JDCB cannonball bike was 17x41 & 27x40 (had a home made clutch drum sprocket on it)
I got all new sprockets from Jon Neuman & am putting 18x43 & 28x44 on it.
i am curious how it will ride. I could get 75mph out of it before, but really don't like to run it that hard.

[Steve Swan]

Steve, the ration on my 25JDCB cannonball bike was 17x41 & 27x40 (had a home made clutch drum sprocket on it)
I got all new sprockets from Jon Neuman & am putting 18x43 & 28x44 on it.
i am curious how it will ride. I could get 75mph out of it before, but really don't like to run it that hard.

That first set of ratios is interesting! Your 2nd set of ratios is same as mine; as i previously mentioned it seems like 55-60 mph is the range best suited to these ratios. The old timers were used to the 35-45 mph speeds they were able to go, for the majority of that was as good as it gets, they didn't have motorcycles like we do these days that could go faster. So,at least in my mind, it's been a matter of awareness and acceptance that these 100 year old bikes aren't designed for higher speeds like we expect.