Topic: 1977 -78 750f supersport

[HAULINHONDA]

what is this I hear about 77-78 f droping valves? I seen 57000 plus miles and still running fast??    Thank you...

[Nayl]

As I understand it, the head on the F2-3's was changed to accomodate bigger valves, resulting in premature wear of the valve guides. 

[flybox1]

As I understand it, the head on the F2-3's was changed to accomodate bigger valves, resulting in premature wear of the valve guides.

..and guide seals.

[700504]

Valve guide keepers are different, basically with a hard enough throttle pull; the valve will pop out from the keeper. But bear in mind that it may be case to case and due to premature wear.

Cyclex has a small write up on this page, where you 'The Problem'

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

[seanbarney41]

Dude, you now have 3? Threads on the same subject?  You can post twice on the same thread, ya know.

[madmtnmotors]

He now has four threads with this exact same topic...

https://www.brainyquote.com/quotes/quotes/a/alberteins133991.html

[HAULINHONDA]

ONLY 3 ADS ,DO YOU HAVE AN 77F2?

[HAULINHONDA]

THANKYOU

[flybox1]

Anyone with a 77 or 78F can answer your questions...and they have been answered.

[madmtnmotors]

ONLY 3 ADS ,DO YOU HAVE AN 77F2?

YES, I have three CB750 F2's.

And I count four "ADS":

http://forums.sohc4.net/index.php/topic,164814.msg1902562.html#msg1902562

http://forums.sohc4.net/index.php/topic,164831.msg1902820.html#msg1902820

http://forums.sohc4.net/index.php/topic,164832.msg1902826.html#msg1902826

http://forums.sohc4.net/index.php/topic,164819.msg1903133.html#msg1903133

Treat them right, change the oil regularly, and they will last many miles just like anything else. Take it out drag racing with constant rips to redline (or above) and you'll likely see premature wear with a greater potential for "dropping a valve".

[Stev-o]

what is this I hear about 77-78 f droping valves?

Never heard about them droping valves!

[flybox1]

Valve guide keepers are different, basically with a hard enough throttle pull; the valve will pop out from the keeper. But bear in mind that it may be case to case and due to premature wear.

Cyclex has a small write up on this page, where you 'The Problem'

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

IMO the chances of a keeper being tossed are minute.  The valve guide would wear first (eventually), accompanied by smoking/burning oil. 
That's your sign.   If it aint broke, dont fix it. 
Keep it tuned up and ride it regularly.  Just watch for burning oil/smoking.  Then you know a top end is due...

[madmtnmotors]

what is this I hear about 77-78 f droping valves?

Never heard about them droping valves!

Valve guide keepers are different, basically with a hard enough throttle pull; the valve will pop out from the keeper. But bear in mind that it may be case to case and due to premature wear.

Cyclex has a small write up on this page, where you 'The Problem'

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

IMO the chances of a keeper being tossed are minute.  The valve guide would wear first (eventually), accompanied by smoking/burning oil. 
That's your sign.   If it aint broke, dont fix it. 
Keep it tuned up and ride it regularly.  Just watch for burning oil/smoking.  Then you know a top end is due...

The later Keepers (77/78 F and 78 K) are different than the early models. The keepers have a steeper angle and can be coaxed into pulling through the stamped steel spring retainers when coupled with vigorous and sustained application of high rpms. CycleX is the only source I am aware of for the "heavy duty" spring retainers that accommodate the later keepers. These are cheap insurance.

The more common problem, as described in more than one of the threads linked to above (IIRC) is the side loading of the valve stem on the valve guide can lead to faster wear of the valve guides in the 77/78 F2 models. Again, sustained high rpm use, combined with neglect,  accelerates this condition. Strict maintenance and reasonable use will reward you with many miles of trouble free operation, just as with any other I.C.E. 

[flybox1]

Good info Wilbur!

[700504]

what is this I hear about 77-78 f droping valves?

Never heard about them droping valves!

Valve guide keepers are different, basically with a hard enough throttle pull; the valve will pop out from the keeper. But bear in mind that it may be case to case and due to premature wear.

Cyclex has a small write up on this page, where you 'The Problem'

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

IMO the chances of a keeper being tossed are minute.  The valve guide would wear first (eventually), accompanied by smoking/burning oil. 
That's your sign.   If it aint broke, dont fix it. 
Keep it tuned up and ride it regularly.  Just watch for burning oil/smoking.  Then you know a top end is due...

The later Keepers (77/78 F and 78 K) are different than the early models. The keepers have a steeper angle and can be coaxed into pulling through the stamped steel spring retainers when coupled with vigorous and sustained application of high rpms. CycleX is the only source I am aware of for the "heavy duty" spring retainers that accommodate the later keepers. These are cheap insurance.

The more common problem, as described in more than one of the threads linked to above (IIRC) is the side loading of the valve stem on the valve guide can lead to faster wear of the valve guides in the 77/78 F2 models. Again, sustained high rpm use, combined with neglect,  accelerates this condition. Strict maintenance and reasonable use will reward you with many miles of trouble free operation, just as with any other I.C.E. 

Definitely, if you don't plan to abuse it or if you plan to ride and not do routine maintenance then you'll be hurting. Just shift before the redline and change your oil!

[seanbarney41]

Wilbur, how many miles on your f2/3 without replacing guides?  I thought like you until, just like clockwork, at 28k, lots of smoke and oil consumption.  Mine was not babied by previous owner, or me, and sat for several years.

[madmtnmotors]

Wilbur, how many miles on your f2/3 without replacing guides?  I thought like you until, just like clockwork, at 28k, lots of smoke and oil consumption.  Mine was not babied by previous owner, or me, and sat for several years.

The highest mileage one I have is around 50,000 miles that has the original guides AFAIK. Serious abuse in the form of three trips to the burnout pit till the tire popped at the Iron Horse Saloon up in Ormond Beach (over the course of four riding seasons) led to premature ring failure on that one. I did replace the valve seals around 30,000 miles and it continued to work well (smoke free) until the aforementioned abuse eventually created such a loss in compression that the bike would no longer get above 70mph! 

I will likely build this one as a successor to my "Evolution" project that is currently performing drag bike duty. The F bike will hopefully get some "magic head" work from either Mike Rieck or A.P.E. along with:

>High compression pistons
>Stronger rods
>Undercut trans
>New cam and primary chains with tensioners
>New primary drive rubbers
>Lightened and balanced alternator

Plus whatever other farkles I think might be necessary to create more "go fast", even if they are only figments of my imagination...   

[seanbarney41]

Wilbur, how many miles on your f2/3 without replacing guides?  I thought like you until, just like clockwork, at 28k, lots of smoke and oil consumption.  Mine was not babied by previous owner, or me, and sat for several years.

The highest mileage one I have is around 50,000 miles that has the original guides AFAIK. Serious abuse in the form of three trips to the burnout pit till the tire popped at the Iron Horse Saloon up in Ormond Beach (over the course of four riding seasons) led to premature ring failure on that one. I did replace the valve seals around 30,000 miles and it continued to work well (smoke free) until the aforementioned abuse eventually created such a loss in compression that the bike would no longer get above 70mph! 

I will likely build this one as a successor to my "Evolution" project that is currently performing drag bike duty. The F bike will hopefully get some "magic head" work from either Mike Rieck or A.P.E. along with:

>High compression pistons
>Stronger rods
>Undercut trans
>New cam and primary chains with tensioners
>New primary drive rubbers
>Lightened and balanced alternator

Plus whatever other farkles I think might be necessary to create more "go fast", even if they are only figments of my imagination...   

Thanks, that is interesting.  Mine still runs very strong, so guessing compression is fine, but the oil consumption has gotten really bad.  I treated it no different than my earlier 750's, so I just assume the earlier engines can just take more abuse as I have never had to retire one due to oil burning (plenty of oil consumption due to leaking though!), even after 70-80,000 miles of such treatment.

[HAULINHONDA]

SORRY FOR POSTING TO MANY AND THANKYOU FOR REPLY .I THING THEY ARE GREAT BIKES AND YOU ARE RIGHT ON .....MY FRIEND HAD ONE FOR YEARS NEVER HAD A PROBLEM UNTILL HE SOLD IT AND GOT AND OLD AMF SPORTSTER OUCH...FINDING OUT LOTS OF STUFF HIGH LIFT CAMS HEAVY DUTY VALVESPRINGS 2MM BIGGER VALVES AND BETTER CLUTCH SPRINGS,...I JUST GOT ONE AND THE VALVE TALK GOT ME WORRY....THANKS AGAIN

[HAULINHONDA]

THANKYOU

[HAULINHONDA]

THANKYOU

[HAULINHONDA]

THANKYOU

[754]

I think your caps lock is stuck...stuck....stuck...stuck..