[Jack D]

I have been wondering about why the cam chain tensioners are supposed to be loosened when checking the valve clearance. Rotating the engine CCW is pulling the chains snug in the operating direction whether the tensioner on the take-up side is tight or loose. Valve spring pressure cannot turn the cam backwards without turning the crankshaft if the tensioner is tight or loose. If the tensioner is loose then valve spring pressure could turn the cam forward. Measuring valve clearance is supposed to be done on the heel of the cam between the acceleration ramps. Accurately locating the cam is a must. Having the cam chain loose which could allow the cam to turn forward seems counter intuitive. I checked my valves two times on the initial adjustment without loosening the chain adjusters. One was with the timing marks and the other was by opening the valve on the opposite to it's maximum lift. Both methods checked the same. I have not encountered any other engine that stated to loosen the cam chain tensioners when checking valve clearance. I have certainly not done valve adjustments on every engine made but I have done a large variety of makes, models and years. Any theories out there as to why Honda says to do this?

 

[backwoods]

Jack, I agree. Obviously the tensioners need to be released if you need to remove the cam to make an adjustment. But, like you, I don’t see any reason to release them just to check clearance.

Does anyone know why the tensioner being loose or tight would affect the valve clearance reading?

 

[Dr Detail]

I was watching Fred's video last night and was wondering the same thing. The only thing I could come up with is if there is any wear in the cam bearings maybe that tension would pull the cam in closer and give a false reading. Tighter at one end and loser at the other. Don't know if this makes sense, just a thought. I was really curious about this as well, maybe some one who knows will chime in.

 

[salyzyn]

http://www.gl1800riders.com/forums/view ... hp?t=41805

 

[Fred H.]

I have found that in some cases, loosening the tensioner can make about a .0005 (half a thousandths) difference in the measurement on some of the forward most valves. Not every time, but sometimes.

The cams float on a layer of oil which is between the cam bearing surface and the bearing surface on the head. When there is no oil pressure, this creates a VERY small gap between the cam and head. With pressure on the chain at the front of the cam, it could be enough to cause the cam to shift in VERY slightly, which may throw off your measurements.

Again, most of the time it doesn't seem to make a difference, but if you have a forward valve that is right on the edge of getting the proper feeler gage under it, it could be enough to make it go from a no-go fit to a go. I have seen that happen on at least one valve on my bike.

My advice would be if you find a valve out of tolerance, before you pull the cam, loosen the tensioner and recheck it, and see if it makes any difference. You are going to have to loosen it anyway to pull out the cam.

 

[Jack D]

As long as we are trying to be accurate, and we need to be with the small variance Honda calls for, how many of you actually measure your feeler gauges? I was checking my ST1100 valves and noticed that the measurements were off from the time before. I have several sets of feeler gauges so decided to measure the gauges with a micormeter. I was quite surprised to see how far off some of the gauges were. I now have some selected gauges for the GL. By the way, one of the gauges farthest from it's supposed value was made by a well-known and quite expensive tool supplier that sells from tool trucks.

 

[Ed Jenkins]

As the engine gets more miles, the loosening of the cam tensioner becomes more important. New engine, very little difference, old engine, small difference. This information is based on my former 01, with 190K on the odo at tradein.

Ed Jenkins, Pawnee, Il
07, 7,000 miles