Joined: Jul 2009
Location: Chandler, AZ
I have a 1964 Ford 200 ci straight six with over half a million miles on it. The head has never been off (been in the family since new, I am now the proud owner) It is starting to burn a little oil, but timing is still spot on, it has a geared cam drive. Still has good compression, I think the valve guide seals are leaking. Oh well, helps lubricate the valves.
The average lifespan of a timing chain/sprockets on a '70s American car is under 100,000 miles. That is still true, even if you replace it with a new 2012 timing chain. Ford, GM, and Chrysler used PLASTIC cam sprockets supposedly because they were quieter. When the chain got some excess play in it, it quickly stripped the teeth off the sprocket and destroyed the engine. If you replaced the cam sprocket with a steel one, and replaced the chain every 60,000-70,000 miles, these engines, properly maintained, could easily last half a million miles. That's five times as long as the stock chain and sprockets would last. People said the engines were no good because few made it much past 100,000 miles. Most of the reason for that was cam drive failure, either total failure, or running the engine for thousands of miles with the timing way off because of the worn chain, before it finally failed. My inline six has no chain or plastic sprocket, so it did not fail.
Very few motorcycle engines make it past 100,000 miles. The most notable exception is the Goldwing. The main reason those engines last so long is because they use cam drive belts, which must be replaced on a regular basis. They do have a primary chain, which unlike Harley's, runs inside the engine case. This is a HUGE chain, way bigger than it needs to be. But since it drives the transmission, the engine will still run even when it gets worn. You just get more driveline lash and clunkier shifting, They also have a starter drive chain, which, even though it is only used for starting the engine, tends to fail around 100,000 miles. It doesn't do any damage, but you have to pull the engine and remove the back cover to replace it. This was just bad design on Honda's part. A direct gear drive would have been the way to go.
Because My beloved Vulcan 750 has FOUR cam chains, and 74,000 miles, I have good reason to expect a catastrophic engine failure in the not too distant future. Replacing these chains requires a total engine teardown, including splitting the cases. When it fails, I'll just replace the bike. I always new it was disposable. What I like about Harleys is that they can easily be rebuilt over and over again. The old EVOs would last about 100,000 miles, you took them apart, honed the cylinders, replaced the rings, replaced the bearings, and put them back together again. Everything could be reground/rebored, and bearings/pistons/rings came in several under/oversizes. You could rebuild the engine about 5 times before you started needing to replace expensive parts. That is no longer the case with the twin cam. When the cam drive fails, it tends to destroy a lot of expensive parts. And I have been inside the twin cam engine. The chain is smaller than a bicycle chain, and the tensioner is somebody's idea of a joke. If they were going to use a chain, it should have at least have had a manual tensioner. But, since the cam drive assembly is so easy to get to, you can still save your engine by replacing it every 20,000 miles or so. It doesn't say that in the book, but it will make your engine last many times longer.
Time to give this up for the night and get ready for bed. Need to be up at 5:00 in the morning to go to my job that I have had for the past 35 years, as a professional auto mechanic.