Keith Marshall on the Cam Problem

Shortly after the article in Performance Bikes magazine came out, I received email from Keith A. Marshall of Heschimura Racing. Keith is a former pre-production tester with American Honda. Here's what he has to say about the cam problem. My comments are interspersed in [].
I have been road racing Hondas for over two decades. Our team, Heschimura Racing, has won three 24 hour races and one 30 hour race. We won the 24 Hours of Nelson's in 1983 on a VF750. Beating all the 1 liter machines in the race on a stock VF. I was sold!

During my career in the motorcycle industry I worked for Honda Research of America, in Torrance CA. We were responsible for testing pre-production units to make sure they would last the life of the warranty and we did emission testing. We rode all models of Hondas for tens of thousands of miles without ever changing any fluids. The only maintenance we were allowed to do related to safety, tires, brakes etc. We tested many V4s that had the poorly designed heads. We NEVER had a cam failure during all the testing we did. We would put over 30,000 miles on the bike without ever changing the oil! This had to be done to check for compliance with the Federal laws concerning warranties.

A typical day of testing started with a thorough check-over of the machines and topping off any fluids, airing the tires, etc. The machines would then be started and HEATED up to OPERATING temperature before riding. We then proceeded to flog the machines for approximately 350 miles per day.

Of all the items I have read about the cam problem I cannot think of one that addresses the cause of the problem. So here is my take, from my experiences in the industry. First and foremost Honda decided to save money on the construction of the head assembly by not align-boring the cam journal-head assemblies. This procedure is performed on all of plain bearing crank Hondas prior to this with some exceptions. Instead they generically milled the heads for the cam bearings then made generic, open journal, cam holders. This saved costly machining operations and allowed individual replacement of the cam holders. This also allowed the cams to move around quite a bit in the head, especially since the cams were short and not rigidly supported. More so than a cam in an align-bored head. This movement caused the edges of the lobes to take the bulk of the load on the rockers instead of the flat surface of the lobe. [Certainly on the cams I've seen, it is the edges that fell to pieces first, although I've also seen signs of slight scoring on the flats. -- RBL] This along with the standard hardening process started to destroy the coating of the rockers and the lobes of the cams. The gear driven versions are align-bored to keep the cams from moving around and keep the gears in mesh. The later year, chain driven, Magnas are align-bored to CURE the problem.

There is another problem with ALL Honda model cams, and probably other make cams, that is not related to the above problem but is mistakenly associated with the design problem. Cams may develop pits that look something like blue cheese pits (the only example I can think of). This is caused by defects in the manufacture of the cam. This problem as been around, I think, since day one. I've seen the defect on all models from 50's to 1500's. [Agreed -- I've heard of cam problems on mid-80s GSXRs, among others. --RBL]

All the fixes that are out there are just Band-Aids on the wound. The V4 can and has lasted for many miles without cam failure, and without expensive oiling modifications. The key to keeping them alive is to take extreme care of them. The most damaging time of an internal engine's life is when it is first started. The ideal situation is that the engine is not put under load until it up to OPERATING temp. Not merely WARMED up! I mean engine HOT not people WARM.

All the fixes you have on your page will and have helped to keep the V4 alive. Since we cannot redesign the heads, at least not on the money I make, the fixes are the way to go. I also know that the brand and type of oil will affect the life of the cams. Since the design puts undue stress on the cam lobes and rockers you need excellent oil.

About the cam adjustment tool that holds the cam up against the cam holder. What is happening here is the tool overcomes the pull of the cam chain to place the cam against the load surface to make the adjustment. This helps to keep the cam from moving around (rocking around(?)) in the head as much. This can cause lots of other problems. If the machine was in good tune before using the tool then after adjusting the valves the idle will be lower. You will have to increase the idle with the idle screw. If all the carbs are in sync and the carbs are in good shape then you will probably be OK. On the other hand you may experience fluctuating idle speeds and stalling. There are lots of frustrating problems associated with adjusting the cams and I do not have the time to go over them all now.

Thanks for reading my opinions. V4's forever!!!!

Check out my web page.

Keith A. Marshall

Interesting stuff, n'est-ce pas? I asked Keith some further questions...

Robyn: It would seem that you avoided cam problems solely by full warm-up before riding. This is quite surprising. At what RPM did you warm up the engines? My understanding is that a decent oil pressure is not developed until at least about 3000 RPM.

Keith: Oil pressure is not the problem as the cam bearings are not fully enclosed as in an line-bored cam. All the oil kits being installed simply increase the flow of cooling oil to the cam lobes, which are not dependent upon pressure as much as flow.

Robyn: When you talk about the later-year chain driven Magnas, you mean the current VFR-based model (which has chain final drive in addition to chain cam drive) right?

Keith: Yes the current Magna is line-bored. The simple way to tell if the cams are line-bored is look on the side of the head where the end of the cam would come out of if it were long enough. If there is a half disk rubber insert in the head side, then it is line-bored, since that is where the boring machine entered to bore the hole.

Robyn: I agree about initial start-up concerns. You'll recall I talk about pumpability of oil at start-up and the suggestion that a heavier oil is worse in this context. But at what RPM do you suggest "idling" the engine to get it fully hot while avoiding both inadequate oil pressure from too-low RPM, and potential wear/damage from too-high RPM while the engine is still cold? The Sabre owner's manual just says to let the bike idle until two bars appear on the display. That takes a very long time at idle, with little oil pressure.

Keith: Once again the oil pressure is not the problem in regards to the cams. And ALL engines need to be heated up. But in real world situations no one does. I know it is bad but I do not heat it up enough. But I also do not stress the engine while driving it until the engine is up to temp. Life is full of compromises. Also do not use heavy oil in these size plain bearing engines. The plain bearing tolerances in the crank and rod bearings are way too close to provide proper lubrication and heat dispersal if you use thick oils. We NEVER use oil over 30W in the racing engines!

To expand on Keith's advice I would caution people not to let the bike idle for a long time with the choke on. This provides too rich a mixture which fouls plugs and, I've read, can also lead to cylinder wear by diluting the oil film that lubricates the piston's motion. When I warm up my Sabre, I take it off the choke as soon as it's able, and then use a throttle lock to keep it idling around 2,000 RPM until fully warmed up.