Topic: CB750/4 - finding neutral

[Steve Campbell]

Would appreciate any pointers re this issue. It has become increasingly difficult to locate neutral from 2nd gear when coming to a red light  stop sign etc.
The shifter will often find first and then it's also difficult to select neutral from first. But sometimes it seems just the slightest touch will find neutral. Finding neutral used to be child's play but now .... grrrr!
Any advice much appreciated.

[newday777]

Howdy Steve
That is on your 1974 K2?(I looked at your other posts from today to see what year your bike is)
That is exactly the same problem that Sean(The Lone Builder, member from France via Belfast Ireland,  Belfast 2 Belfast by Bike) had on his 1974 K2.
He stayed with me a year ago in New Hampshire on his tour through the US and Canada. When he arrived he wanted to check the clutch pack thinking it was the problem. No. All the clutch parts were fine. I called HondaMan about it and he said he had run into this over the years on several bikes and motors he had worked on.
Pull the transmission cover off(shifter cover). There is a large screw holding the large plate with a V notch washer that comes loose that locates the shifter mechanism in place on the end of the shift drum. Remove the screw(JIS #3 or an allen head screw ?). Clean the threads and put some blue Loctite on the threads to secure it. (It was originally staked, and not very good job of staking it was the problem)

[scottly]

It's normally easier to find neutral while the bike is still rolling than once stopped. If the problem seems to get worse over time, you might want to check the clutch adjustment, starting with with the adjuster at the clutch cover. There should only be 1-2mm of free play in the end of the lever when pressed with your finger.

[PeWe]

Can also be oil related.
Some 20W-50 motorcycle oils make shifting smoother on these bikes, like finding neutral when engine is hot and standing still.

[Don R]

 My 76F would tell me when it wanted an oil change. The shifter became fussy.

 My old drag bike had a loose shift ratchet stud, behind the nut in the above picture. when I attempted to put a helicoil in the case I discovered that it already had one and the stud threads were worn. I replaced it with a better one and loctited it into place. No troubles since.

[Steve Campbell]

Thanks guys, for pointing me in the right direction. Really appreciate you taking the time.

[scottly]

Something else to check is the clutch lever hole and pivot bolt for wear. I started having trouble with my clutch dragging; even with the cable adjusted for minimum play there was an inch or more travel at the end of the lever before the cable would start to move at the clutch cover end. Over the decades of ownership, both the hole and bolt were noticeably worn, leading to the play and loss of travel of the clutch mechanism. I replaced both with less worn parts, and also started adjusting the clutch the way I mentioned earlier.

[HondaMan]

Oil.
Oil.
Oil.
Today's oils lack ZDDP (zinc) in them because it damages catalytic convertors in vehicles so equipped. These bikes REQUIRE it be used to make the clutches stop dragging, which increases shifting difficulty when stopped. You can add ZDDP by buying it (I get it on the Internet at eBay, 1/2 of a 4-ounce bottle is sufficient if you have the wrong oil). It takes about 150 miles for it to distribute itself through the engine and clutch. It also increases the oil life: if you use, say, the [correct] Bel-Ray EXL Mineral oil and 2 ounces of ZDDP you can make 2000 miles between changes and all will be fine. Otherwise the changes must be more frequent, like 1000-1500 miles.

The 750 is more balky about shifting when sitting still than any other bike I've ridden. They were like that when brand new.

[PeWe]

Here where I ordered Zinc. 5.9 ml botttles. I think 1/3 bottle in the first change where 3 L or 3 quarts oil is used.  To cover for all oil in the engine, 3.5L
Maybe 1/4 for the next.

https://ebay.us/m/oMpKDH

Both my bikes got it. But bad weather and winter happened so no test ride yet.

I wrote about it here with the recommended mix to 6 quarts I calculated for 3-3.5L

http://forums.sohc4.net/index.php/topic,61168.msg2331235.html#msg2331235

Edit:
I have searched for info about oils and high temperature 2018 when we had a hot period. Oil tank temp gauge touched the red area of 120*C.

I found similarities when comparing old air cooled Porsches and CB750. Both need 20W-50 oil from ambient temp of ca15*C.
Both need zinc. Cam and crank bearing design. Both are air cooled.

Here is one interesting read that explains modern oils as no good for our engines.
Not finding the neutral when engine is hot and bike standing still is one way to feel the difference. (Clutch and gear mechanism is verified to be good)

https://lnengineering.com/oil.html

This is for those that want an engine that will last longer.
Modified engines with harder spring rates and aggressive cams must have more of the good.