The April 1996 issue of Performance Bikes, a British magazine, contains a retrospective of the development of the V4, from the founding V45 Sabre in 1982 through to the current VFR750F and RC45. Naturally some discussion of the cam problems of the first generation VF motors is included. The authors provides the details on a problem I had previously known only vaguely as "manufacturing variations". They also make explicit reference to problems which I've heard about only anecdotally and have never before seen in print. Without permission, I reproduce this section of the article. Footnotes refer to comments of my own afterwards.
"The big blow came when MCN's (Motor Cycle News) long term VF750S developed abnormal wear on a rear camshaft. At first it was put down to poor metal hardening, but when they printed the tale other VF owners came forward with their own horror stories. A major row blew up with Honda UK at first refusing to acknowledge the problem before coming clean, claiming they were waiting until they'd located and solved the problem before doing anything about it."And the trouble was this: poor oil feed to the cams caused by kinked oil pipes, restricted banjo bolts, and oil bleed holes in the camshafts. All three were cured by changing the oil pipes so they wouldn't kink [note1], using banjo bolts with larger holes and restrictors removed [note2], and drilling extra holes at the base of the cam lobes (and plugging the bleed ends on the camshafts). [note3] Honda also halved the oil change intervals to 4000 miles.
"But there was more. Instead of line boring the cam journals with the caps attached to the head (so the caps were accurately matched), Honda milled them in two separate operations (for neatness, they said). This led to play in the cam bearing, which meant that when setting valve clearances, valve spring and camchain tension tilted the camshaft. This artificially reduced clearance between cam lobes and rocker arms so that what looked right during a service could double when the motor was running. Result: the lobes hammered the rockers, knackering both.[note4]
"To solve the problem Honda produced a special tool to hold the camshaft in place during adjustment [note5], but not before the VF earned a reputation for being unreliable -- the last thing Honda needed with the motor which was supposed to be their super-techno-flagship of the future.
[...]
"For 1985 the 750 [Interceptor] carried on unchanged although Honda returned to line-boring the head and cam cap as a matched pair." [note6]
The following are my comments on what Performance Bikes said.
[1] I have never heard of kinked oil pipes until this article.
[2] If you have read my other cam articles you know that Phil Rastocny noticed the upgraded banjo bolts after some detective work with the Honda parts microfiche. His oil modification scheme calls for replacement of these bolts and/or drilling them out for greater flow. I have never seen anything "official" on this subject until now.
[3] You may also recall that my own V4 mechanic told me about the changes to the later camshafts, and that when I swapped engines he welded the ends of the camshafts closed as he had seen on the later model camshafts. Again, I've never seen anything official about this before.
[4] This seems like a key downfall in the VF valvetrain. Mention has often been made of tilting camshafts and the need for the special tool, but this is the first time I have ever seen this explanation for what caused it. Shortly after this article in Performance Bikes appeared, I received email from a fellow in the U.K. who is a former Honda development tester. He describes the same thing. In my original article on the cam problem, I list the item "Variation in cam-to-bearing clearance because of manufacturing method." Now at last we know exactly what this was referring to.
[5] When I adjust my valves, I not only use the special tool, but I position the cams differently from what the manual recommends. My V4 mechanic taught me this. Don't bother with searching for TDC and lining up the timing marks. When you do this, the cam lobes are not pressing on the valves anywhere. Instead, rotate the crank so that the cam is at full lift on the opposite end of the camshaft you're working on. Now install the special tool at the end you are working on. This results in both ends of the camshaft being forced up against the cap, so there is no tilt. Please note that this is not an official procedure recommended by Honda. It is merely the method that my mechanic taught me, and it seems to work well for both of us.
[6] I've never heard of this change to the 1985 Interceptor. Any owners of this model are welcome to send me mail with your observations. You should be able to spot two half-circle rubber gaskets on the cylinder head where the valve cover meets the cylinder head.
Looking at photos of the 1987-8 V45 Magna (the one with the four upswept pipes and solid disc rear wheel) it seems to me that it has gaskets like this, implying line-bored cam journals and thus safety from the cam problem.
Greg Lazarian (greg_lazarian@pobox.tbe.com) tells me his 1986 V45 Magna is line-bored, so that's a good sign.