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Tech Tips

Chain Tensioner Wear on Your Twin Cam Engine

I have recently heard a lot of noise about a maintenance item you may be overlooking in your Twin Cam Harley-Davidson.

I have read many different listings that refer back to a problem that has been identified in a few late model Twin Cam engines. This tip is not targeted for all Big Twin models; however, when I come across a subject such as this from our readers, I feel we need to spread the word as quickly as possible to help you prevent costly repairs.

Since the cam chain is a one-piece chain that has no master link, the only thing that can be done with the chain is replace it after it has stretched beyond service limit. This does happen on metric bikes as well, so nobody is exempt from the cam chain style setup. You who own the gear-driven camshaft setup are exempt from this failure.

When it comes to getting correct information on Harley-Davidson repair procedures, I seek the advice of Dyno Mike Wilson, owner of Dyno Mike's Dynamic Chassis. According to Mike, cam chain tensioner wear is not specific to synthetic or standard 20W50 motor oil. Over the last 10 years he has seen engines that have had 20K miles and some that had 30K+ miles on them with the same problem.

Our main concern is, once the material on the chain tensioner shoes has worn in a groove-type pattern, usually the side breaks off and it won’t be long until metal-to-metal contact. Once this happens, engine failure is imminent around 3,000 miles from that point.

Mike believes the cause of this failure is the pitch on the cam gears themselves. The variation in pitch will cause the cam chain to burr and start ruining not only the crankshaft and oil pump, but other parts as well, including the cams and cam plate which will be a very costly repair. The problem seems to occur whether you run the motorcycle hard, add stiffer valve springs, or change from a stock to high lift camshafts. There are a lot of theories people are talking about, but whenever you see excessive wear on a cam chain tensioner, you will be able to remove the cams and cam plate to inspect for wear. When you come across a cam chain that is very stiff, not “kinky,” this is where Mike sees the most wear on these parts.

A lot of people get extremely concerned when they hear the word “camshaft”; however, when it comes to an item that costs as much as a set of tires, consider the facts. When you replace your tires, it usually runs about $400. They only last 10000 miles, so ask yourself, “Is this a chance I want to take?”

Mike can replace these tensioners, change the oil and filter, including all the necessary gaskets, for around $400 including labor. This is a maintenance item you should have inspected at 20000 miles, and according to Mike, he can perform this inspection for around $35.

On the newer model Twin Cam engines Harley-Davidson has completely done away with the spring-type tensioner and replaced it with a hydraulic-type system that gives unsurpassed life, with almost no wear.

Below is a response Dyno Mike Wilson submitted to one of our forum readers on this topic, which I also wanted to share with you:

This is a very commonly asked question and a big concern of all the Twin Cam owners. Being in the performance field for over 10 years I have personally looked inside hundreds of Twin Cam motors and have seen first hand a variety of wear patterns on several internal parts.

First, the Twin Cam had a problem with the cam chain gear sprocket bolts, which was actually more of a key way problem in the gear itself. I saw several that failed when the bolt was still intact. The key in the big gear only had about 20% engagement in the shaft. Harley finally did away with this design and replaced it with a splined shaft and gear, which solved this problem.

The next was the B motors and the threat of the balancers being over-revved. I personally only saw one motor failure from this and the problem existed only because the shaft that turned the balancing weight chain gears only engaged about halfway through the drive gear. This was caught and redesigned half way through the production year in 2000. I’m not sure that 7000 RPM ignition modules are that harmful to the B motors especially if you realize that lots of metric bikes have balancing weights that turn in excess of 11,000 RPMs. All the motors I build have a 7000 RPM limit in the A and B motors. I stand behind the motor for one full year regardless of mileage. For example, I shift my 103 cubic inch B motor in my Fat Boy at 7500.

Next came the chain tensioner issue, and this is why I don‘t worry about mileage. I’ve seen motors with 2000 miles on them with two broken or worn tensioners. I’ve also seen motors with 75K on them with virtually no wear what so ever on the tensioners. From what I have experienced, the way you ride or what oil you use doesn’t necessarily have anything to do with wear on the tensioners.

One possibility could be on how the cam chain itself is worn. Let me explain what I mean by that statement. The pitch on the cam gears can varies from bike to bike or more so cam to cam. When the gear pitch varies the cam chain will wear prematurely and can cause the chain to develop burns and cause the chain to stiffen up. This can eat into the soft phenolic cam chain tensioner shoes like a chain saw. I would highly recommend replacing the cam chain if you experience any wear on the tensioner itself.

Another thing you should do is inspect the oil pump for scratches on the return side of the pump, because once you have any wear on the internal engine components the oil pump on the Twin Cams can really suffer. Remember the Harley motors are really dry sump motors like what race cars have. The oil is held in a remote location and if the pump gets worn or has any scratches in the return side, the motor will retain oil and cause rapid power loss.

I would recommend checking the cam chain tensioners every 10,000 miles. If you have any other questions or need any further assistances with this problem, feel free to contact me.

If you are hearing some abnormal noises coming from your cam cover it is time to take this to a seasoned tech such as Mike and get the facts, not the hype. I do understand that not everyone lives in the Midwest; however, pick up the phone and call or e-mail Mike he will be glad to hear from you and will answer any questions that have been troubling you about your Harley-Davidson motorcycle.

For more information on this subject or to schedule an inspection, please feel free to contact Dyno Mike Wilson at (816) 322-0379 or at dynomikewilson@aol.com

By Dave Miller

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25k mile tensioners with acceptable wear patterns using synthetic oil 20k mile tensioners using H-D 20w50 conventional oil 30K mile tensioners that have broken the side plate
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