Topic: Valve Question

[Vintageguy]

On Facebook the other day (not always a good start) I read a post that a gentleman put up regarding 1978 CB750F's that gave me pause to ask this question; Are 1978 Honda CB750F's known to "drop valves" frequestly? If so, this is the first I've heard of it. The individual putting up the post claimed to be an old certified Honda mechanic from back in the day, but I was under the impression that the  750F engine was really quite bulletproof, and in fact superior to the 750K engine of the same year in every way. If any one has any information on this topic I'd sure love to hear it. Thanks.

[70CB750]

There is info on Cyclex web page:

http://www.cyclexchange.net/Honda%20cb750%20(%2077-78%20)%20%20F%202%20Section%20Page.htm

From what I know, Honda was trying to keep up with other companies when they went to DOHC and boosted the 78 SuperSport using different valve train.  In long term this boost showed to be problematic. 

[69cb750]

I have owned both.
Both are reliable.
You can beat either to death if that is your intent.

[Vintageguy]

Thanks for the input.

[bryanj]

F 2 & 3 wear exhaust valve guides at a quick rate and if not replaced will cause dropped valves BUT the amount of blue smoke from worn guides makes it difficult to ignore!!!!

[Vintageguy]

Thanks brianj (and all) for the responses. Yes, I'm sure the telltale is the blue cloud behind your bike. Thankfully, mine has none of that so far. Thanks, again.

[low-side]

My recollection is that the different keeper design could fail if operated at very high revs for an extended period of time.  I've seen a couple of heads where it happened.  If you're just riding it mid-range with occasional runs near redline I wouldn't worry about it.  If you run with the throttle  constantly pinned you might look into some of the aftermarket valves that address the keeper issue. Worn guides certainly don't help either.

[Vintageguy]

The good news is that I don't pin my rev's at all. If anything, I could probably be accused of babying my stuff too much. I do run in the mid range frequently, but even at that at the low-to-middle end of mid range. Never blown an engine ever, and that could be why. Born working poor and always had to fix my own stuff when I broke it. Thank you for the responses. Love this forum. Always helpful and informative,  without typical on-line forum judgement.