Author Topic: is the valve adjustment from manual correct? 1978cb750f  (Read 8902 times)

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Offline jamesianyoung

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is the valve adjustment from manual correct? 1978cb750f
« on: March 10, 2012, 12:00:07 AM »
I recently purchased a 1978 cb750f that is a restoration project. I  have only experience with looking things up on the internet. This is my first bike. It hasnt been started in "two years" according to the seller and 15 years before that. I bought a new battery and attempted to run a compression check but the the no.2 cyclinder was difficult to remove the plug and then difficult to thread the compression gauge. All other cylinders read approx. 100 psi but the number two was 60 everytime except the last reading which was 90 psi, then the gauge broke. I returned the guage so i wouldnt have see 60psi again, lol. Thought maybe the threading was probably the issue and reinserted plug.

I decided to just move forward and adjust the valves. Here lies the issue. The manual states that you need to find tdcc on the no.1 in. and ex. , the no.2 ex. and the no. 3 in. and the rest at tdc. Well i couldnt get any clearance on the no.2 ex. and the no. 3 in. at tdcc after verifiing that the pistons were at compression tdc not tdc. I did read one thread that stated it was the opposite for the no.2 and no.3 so i tried that and its was simple and easy. I started it after doing it and it idled with some taping. This frightens me though.  Any comments?

One last question. I painted the engine and put miracle oil in the top end. When idling it starts to smoke from the ex. of the engine within a minute. No oil leaks that are apparent. Exhaust leak, head gasket, paint burning????

Offline City Boy

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Re: is the valve adjustment from manual correct? 1978cb750f
« Reply #1 on: March 10, 2012, 07:17:21 AM »
Hi You must make sure cylinder#1 is on compression stroke.Turn crank clockwise till you see cyl 1 intake valve open and close then continue turning till cyl 1/4 TDC mark shows on advancer.Then you can set #1 in and ex,@2ex,and #3 in.Now repeat process using #4 in.as reference then set remaining valves.
     Good luck and Rock On
'52 Kiekhaefer Mercury Rocket Hurricane KG4H
'70 750/RC 1000 Original Owner
'83 1100F

Offline CycleRanger

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Re: is the valve adjustment from manual correct? 1978cb750f
« Reply #2 on: March 10, 2012, 08:19:09 AM »
One last question. I painted the engine and put miracle oil in the top end. When idling it starts to smoke from the ex. of the engine within a minute. No oil leaks that are apparent. Exhaust leak, head gasket, paint burning? ???

Smoke is coming from the exhaust pipes?  Or the crankcase vent?
Have you changed the oil since you got the bike?

How many miles are are on this bike?
Do you have a copy of the Honda Shop Manual or Parts List for your bike? Get one here:
https://www.honda4fun.com/materiale/documentazione-tecnica
CB750K5        '79 XL250s     CL350K3
CB750K3        '76 XS650      '76 CJ360T

Offline MCRider

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Re: is the valve adjustment from manual correct? 1978cb750f
« Reply #3 on: March 10, 2012, 09:23:16 AM »
Follow CityBoy, don't add anything to it.

AS the #1 intake valve rises (closes) look for the 1-4 T mark and stop, Shortly after the #1 IN stops rising.

Then set #1 In & Ex; #2 Ex; #3 IN

Rotate 360deg and set #4 IN/EX; #3 Ex; #2 IN

easy peasy.
Ride Safe:
Ron
1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
"Sometimes the light's all shining on me, other times I can barely see, lately it appears to me, what a long, strange trip its been."

Offline lucky

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Re: is the valve adjustment from manual correct? 1978cb750f
« Reply #4 on: March 10, 2012, 09:34:12 AM »
One thing the book does not tell you about adjusting valves.

The intake is .002 and the exhaust is .003
( edit)

After you have your .002 thousandths and you think it is right, take a .003 thickness gauge and try to inset it. If it will go in then the correct gap is still not there.

Same for the exhausts.
« Last Edit: March 10, 2012, 02:25:50 PM by lucky »

Offline MCRider

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Re: is the valve adjustment from manual correct? 1978cb750f
« Reply #5 on: March 10, 2012, 09:42:38 AM »
2 & 4?

Or 2 & 3?
Ride Safe:
Ron
1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
"Sometimes the light's all shining on me, other times I can barely see, lately it appears to me, what a long, strange trip its been."

Offline City Boy

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Re: is the valve adjustment from manual correct? 1978cb750f
« Reply #6 on: March 10, 2012, 09:50:06 AM »
Hi.Unless specs have changed for later models and I missed it,correct valve lash for 69-78 CB750 K and F  is .002" In and .003" Ex. for stock camshafts.Non stock camshaft valve lash can vary.The RC 315 cam in my unit is set at .012" IN/Ex.
'52 Kiekhaefer Mercury Rocket Hurricane KG4H
'70 750/RC 1000 Original Owner
'83 1100F

Offline MCRider

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Re: is the valve adjustment from manual correct? 1978cb750f
« Reply #7 on: March 10, 2012, 09:52:37 AM »
Probably just a misspeak.

http://oldmanhonda.com/MC/DataTable.html
His point is well taken though.

Use the 3 to check the 2. Use a 4 to check the 3.
« Last Edit: March 10, 2012, 09:54:17 AM by MCRider »
Ride Safe:
Ron
1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
"Sometimes the light's all shining on me, other times I can barely see, lately it appears to me, what a long, strange trip its been."

Offline lucky

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Re: is the valve adjustment from manual correct? 1978cb750f
« Reply #8 on: March 10, 2012, 02:23:49 PM »
Probably just a misspeak.

http://oldmanhonda.com/MC/DataTable.html
His point is well taken though.

Use the 3 to check the 2. Use a 4 to check the 3.

YES...Thanks MCRIDER I was thinking of a different Honda engine.
Main point is try a .001 larger than your correct measurement to make sure it will not fit.

Offline jamesianyoung

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Re: is the valve adjustment from manual correct? 1978cb750f
« Reply #9 on: March 12, 2012, 10:30:34 AM »
Thanks guys i got it. The smoke is coming from the area close to the crankshaft breather box. I am also having some stuck float issues. I read that this can result in fuel in the oil so im going to replace the oil and take the bowl off to inspect.