Topic: valve damage

[Serge]

Hello,
have you ever seen such damage to the valve ?  how long do you think such valve will last ?
I  got into head gasket replacement affair and I wanted it to be a short one..

Thanks for your advice! - Serge

[Big Jay]

Rocker arm motors have valves with hardened tips for the rocker screw to ride on. Yours has worn thru the hard part.  Tou need to change it and any others like it ASAP.

Jay

[oldbiker]

I would add that when you come to remove these valves, you will most likely find that the valve end has mushroomed and will not slide easily out of the valve guide. DON'T force them out, that will damage the guides. Use a Dremel or something similar to grind down the sides of the top of the valve till it will slide out easily.

[scunny]

I'm with old biker on this one, you will need to file or grind the valve head to remove it without damaging your guides. valves don't cost much.

[upperlake04]

I disassembled the top end  of my 78 750F earlier this winter and found  much the same problem. MRieck, most learned contributor from this site, kindly helped me sort it out  Give him a shout.

[JonnyHonda]

I bought a non running engine for spares, and guess why it wasn't running



to see the bigger picture http://www.honda-sohc.co.uk/index.php?set_albumName=album11&id=100_1868&option=com_gallery&Itemid=&include=view_photo.php

[MRieck]

I bought a non running engine for spares, and guess why it wasn't running



to see the bigger picture http://www.honda-sohc.co.uk/index.php?set_albumName=album11&id=100_1868&option=com_gallery&Itemid=&include=view_photo.php

Is that from an F2? It looks it

[crazypj]

This type of damamage is real common if you have the valve clearances too loose.
 Even  1 or 2 thou is enough. (+0.001"~0.002") The opening and closing ramps on the cam basically dont and the valve gets slammed open.
 I have found even  0.001" out of adjustment drops compression by about 20psi (too loose or too tight)
Relativly easy way to check is to remove the adjuster screws every third or forth service and see if the ends of them have either flats or pitting, then use a flashlight to check valve tips.
If there is any wear ( not at all unusual) its not  too big a deal, you just cant use feeler gauges to set tappets and have to use a rotational amount of tappet screw, turn it in until it just touches and back it off, I think about 1/8th turn, anyone have a tappet screw handy to measure pitch? I think the screws are 0.5mm pitch which is about 0.020" so 1/8th turn will be about 0.0025" (two and a half thou or twenty five tenthousandths if yoiu want to be semantic about it, actually 0.002460624", but I think four one hundred thousandths of inch is close enough when your using a not too precise 1/8th turn )
Just my  experience and opinion
PJ

[crazypj]

I bought a non running engine for spares, and guess why it wasn't running



to see the bigger picture http://www.honda-sohc.co.uk/index.php?set_albumName=album11&id=100_1868&option=com_gallery&Itemid=&include=view_photo.php

that cracked the guide as well did'nt it.
PJ

[scondon]

I disassembled the top end of my 78 750F earlier this winter and found much the same problem. MRieck, most learned contributor from this site, kindly helped me sort it out Give him a shout.

Yeah , give "Modest Mike" a call. He can make'em better than new, Serge, better From what I hear the F2 valves are no longer available so either repair what's there or switch head, cylinders and pistons for "K" type or 75-76 "F".

[JonnyHonda]

I bought a non running engine for spares, and guess why it wasn't running



to see the bigger picture http://www.honda-sohc.co.uk/index.php?set_albumName=album11&id=100_1868&option=com_gallery&Itemid=&include=view_photo.php

Is that from an F2? It looks it

Yep, F2. Gonna be a pain if the valves are unobtainable

[JonnyHonda]

that cracked the guide as well did'nt it.
PJ

Don't know yet, but most likely did, Iv'e just put the head away for know while I clean the bottom end. Thinking about an over bore, (The engine, Not me)

[MRieck]

 If you go 836 put a K head on.

[joeb]

Also if you go with a k head and the f -sleeves  you should get the oil return holes machined on the bottom of the sleeve to  help drain off the oil from the head. Not required but will help keep oil from pooling in the head.   

[rob]

I am interested in this thread.. but I have never looked at the valves on my engine.  Would someone mind pointing me to where the damage is on this?

Also, were there tell tale signs of this valve damage?  noise? performance?

Thanks,

Rob

Hello,
have you ever seen such damage to the valve ?  how long do you think such valve will last ?
I  got into head gasket replacement affair and I wanted it to be a short one..

Thanks for your advice! - Serge

[Serge]

the first sign of such wear is when after setting the gap with feeler gauge it is knocking real loud

[oldbiker]

It is not generally realised that when the valve end is hollowed like this itis impossible to use an ordinary feeler gauge to measure valve clearance. The diagram shows why. Although the gauge is a 2thou feeler th actual clearance is 2 thou plus the depth of the hollowing. This is why I always adjust my valves by closing them up finger tight and then slackening them by one tenth of a turn as shown on my adjusting tool.

[bryanj]

Pitch of the adjuster is 1mm so 1 full turn = 40 thou

[oldbiker]

Bryanj, my bike is a CB400f and according to my parts list the CB750 uses the same part. The pitch is 1/2 mm thus 1/10 turn is 2 thou but the point I was making is about the error in clearance arising from valve hollowing.

[crazypj]

I am interested in this thread.. but I have never looked at the valves on my engine.  Would someone mind pointing me to where the damage is on this?

Also, were there tell tale signs of this valve damage?  noise? performance?

Thanks,

Rob

The 'tube'  you can see in the first post picture shouldnt be there. the tappet has worn its way into the valve. if you try and use a feeler gauge it will rest on the top of 'tube' part and still have about 70 thou plus, clearance when engine is running.
One other thing for all other posters, doesnt the F2 have the biggest valves ever put into a 750 SOHC? I think the head casting was modified to do this (2mm larger than largest possible in std. 750 head) you cannot fit F2 valves to any other 750 motor without fitting F2 head
PJ

[MRieck]

I am interested in this thread.. but I have never looked at the valves on my engine.  Would someone mind pointing me to where the damage is on this?

Also, were there tell tale signs of this valve damage?  noise? performance?

Thanks,

Rob

The 'tube'  you can see in the first post picture shouldnt be there. the tappet has worn its way into the valve. if you try and use a feeler gauge it will rest on the top of 'tube' part and still have about 70 thou plus, clearance when engine is running.
One other thing for all other posters, doesnt the F2 have the biggest valves ever put into a 750 SOHC? I think the head casting was modified to do this (2mm larger than largest possible in std. 750 head) you cannot fit F2 valves to any other 750 motor without fitting F2 head
PJ

You can fit a 34mm intake on a any K/F(75/76) head. No go on anything larger than 28mm on the exhaust with the 34mm intake.

[crazypj]

 doesnt the F2 have the biggest valves ever put into a 750 SOHC? I think the head casting was modified to do this (2mm larger than largest possible in std. 750 head) you cannot fit F2 valves to any other 750 motor without fitting F2 head
PJ

You can fit a 34mm intake on a any K/F(75/76) head. No go on anything larger than 28mm on the exhaust with the 34mm intake.

I sit corrected. (its the posture chair)
 I remember something was done to F2 to allow bigger valves than Honda used in the previous years. I'm pretty sure thats the size of Hyabusa valve which has a 5mm stem, so you can get better flow than with 7mm or 8mm stem and the much lighter valve gives better contol of valve gear at high rpm( maybe aftermarket busa, think std is 33mm?) Anyone building a CR750 for AHRMA?
PJ

[MRieck]

 doesnt the F2 have the biggest valves ever put into a 750 SOHC? I think the head casting was modified to do this (2mm larger than largest possible in std. 750 head) you cannot fit F2 valves to any other 750 motor without fitting F2 head
PJ

You can fit a 34mm intake on a any K/F(75/76) head. No go on anything larger than 28mm on the exhaust with the 34mm intake.

I sit corrected. (its the posture chair)
 I remember something was done to F2 to allow bigger valves than Honda used in the previous years. I'm pretty sure thats the size of Hyabusa valve which has a 5mm stem, so you can get better flow than with 7mm or 8mm stem and the much lighter valve gives better contol of valve gear at high rpm( maybe aftermarket busa, think std is 33mm?) Anyone building a CR750 for AHRMA?
PJ

....yep...that's the thinking exactly sir. (std Busa is 33mm). I have them in my street bike. My only addition would be cut the 5mm guides down a couple of mm at least (port side).

[Serge]

I disassembled the top end of my 78 750F earlier this winter and found much the same problem. MRieck, most learned contributor from this site, kindly helped me sort it out Give him a shout.

Yeah , give "Modest Mike" a call. He can make'em better than new, Serge, better From what I hear the F2 valves are no longer available so either repair what's there or switch head, cylinders and pistons for "K" type or 75-76 "F".

Sean, I actually found out that I have 1978 K engine in my bike. Anyway, the  new valves are not available from Honda or partsnmore.. Does MRieck make them ? 

[jtb]

Mike,  don't sell him my old valves! he he 
John