Topic: New valve ?

[gbal06]

My valves are on the end of the spec for being good. If I buy new ones is it a matter of just putting in the new ones and lapping them or do I need to take them to a machinist?

[kerryb]

I'm no expert at this, but...if you think your valves are near done, shouldn't the guides be checked for wear?  If the guides are still good then how are the seats?,  will lapping provide an adequate seal, or should they be professionally recut?  Further inspection seems in order.  Do you know how many miles are on them?

[gbal06]

Guides and seats are good with less then 2500 on the speedo. I don’t know about PO

[Flyin900]

Something is off there if there is only 2500 miles on the engine, it is  very unlikely that the valves would be worn out of spec.
What spec are you referring to for this assessment? Possibly someone changed out the speedo or the motor/ head?

[gbal06]

I agree. As I take this motor apart   I find thinks are not what they seem. There should be no way everything is at the low end of spec for such low miles. Here are the specs I am using.

[PeWe]

Wiggle valve sideways in guide at 10mm lift or more without springs. It should not be a "clonky" lash.
Exhaust is the common guide to find this wear.
Bent valve if not moving easy in its full working lenght in-out the guide.

I have seen shot valves, the outer edge of dish very thin, sealing surface concave. Jagged edge pieces have fallen off.

Seats to have a shiny ring where valve is sealing. Not too wide. I guess 1- 1.5mm is OK

[754]

Easy to tell if they are worn. Will have  double the wiggle front to back vs sideways.
 Its apart.. measure  everything.. use a mic..

[bryanj]

Put up some pics of the valves and let us see

[gbal06]

I will check the movement and send pics when I get home today.  I mic'ed them and all of them are at the low end of service(which I think is weird). But if I did replace them, is it as simple as buying a new pair and lapping them or does it need to go out to a machinist?

[bryanj]

IF the seats are good just lap them in BUT if they are actualy within spec why bother

[HondaMan]

The valve stems seldom wear in these engines: about 0.0004" is the worst I have seen (unless damaged by water).
MUCH more common is worn valve guides in the post-1971 engines, as Honda switched away from Stellite metal to common cast iron then (except in the 750F0 engines). The iron guides can get rust from sitting, especially if the oil was old, then parked for 10 years, with water vapor then trapped in the guides. It takes about 10 minutes of runtime then to make the guides' holes too big!

[MauiK3]

Check everything in the head, it’s a lot of work to backtrack.
I’m thinking if the valves are worn, so are the guides and seats.
Don’t go to just any machine shop for head work, they’ll butcher it, several here on the forum can help, Hondaman did my head and cylinders, runs perfectly.
Get Hondaman’s book.
Read “Thoughts of Hondaman” here on the forum, very helpful.

[MauiK3]

http://forums.sohc4.net/index.php?topic=7401.0


Thoughts of Hondaman ( Mark Paris)

[maxheadflow]

The valve stems seldom wear in these engines: about 0.0004" is the worst I have seen (unless damaged by water).
MUCH more common is worn valve guides in the post-1971 engines, as Honda switched away from Stellite metal to common cast iron then (except in the 750F0 engines). The iron guides can get rust from sitting, especially if the oil was old, then parked for 10 years, with water vapor then trapped in the guides. It takes about 10 minutes of runtime then to make the guides' holes too big!

Did Honda really use stellite as a guide material?  Rockwell hardness would require carbide reamers and AFAIK they were always cut with high speed steel.  IIRC the valve faces and seat were stellite.

[HondaMan]

The valve stems seldom wear in these engines: about 0.0004" is the worst I have seen (unless damaged by water).
MUCH more common is worn valve guides in the post-1971 engines, as Honda switched away from Stellite metal to common cast iron then (except in the 750F0 engines). The iron guides can get rust from sitting, especially if the oil was old, then parked for 10 years, with water vapor then trapped in the guides. It takes about 10 minutes of runtime then to make the guides' holes too big!

Did Honda really use stellite as a guide material?  Rockwell hardness would require carbide reamers and AFAIK they were always cut with high speed steel.  IIRC the valve faces and seat were stellite.

In the early 750 and the old Hawk engines (CB/CL250/305) they used Stellite, and when disassembled young (like 50k miles or less) they looked like glass inside. They have a slight bluish cast to them, so they are easy to tell apart from the later cast-iron ones. The old Honda shop manuals show a "valve reamer" tool for use in these engines (in the front pages, Tools section), but it took a Serdi machine to ream new ones if installed: they had to be high-speed honed. The valve seats in these same engines were sometimes Stellite and sometimes steel, changing to iron in the (750) K4 engines. I was surprised the first time I found Stellite in the 750F0 engines, and the first-year 750"A" heads also sometimes have them. They are so hard that if the valve stem is bent (like too many RPM) the edges of the guides break off like glass at the port side.

[maxheadflow]

The valve stems seldom wear in these engines: about 0.0004" is the worst I have seen (unless damaged by water).
MUCH more common is worn valve guides in the post-1971 engines, as Honda switched away from Stellite metal to common cast iron then (except in the 750F0 engines). The iron guides can get rust from sitting, especially if the oil was old, then parked for 10 years, with water vapor then trapped in the guides. It takes about 10 minutes of runtime then to make the guides' holes too big!

Did Honda really use stellite as a guide material?  Rockwell hardness would require carbide reamers and AFAIK they were always cut with high speed steel.  IIRC the valve faces and seat were stellite.

In the early 750 and the old Hawk engines (CB/CL250/305) they used Stellite, and when disassembled young (like 50k miles or less) they looked like glass inside. They have a slight bluish cast to them, so they are easy to tell apart from the later cast-iron ones. The old Honda shop manuals show a "valve reamer" tool for use in these engines (in the front pages, Tools section), but it took a Serdi machine to ream new ones if installed: they had to be high-speed honed. The valve seats in these same engines were sometimes Stellite and sometimes steel, changing to iron in the (750) K4 engines. I was surprised the first time I found Stellite in the 750F0 engines, and the first-year 750"A" heads also sometimes have them. They are so hard that if the valve stem is bent (like too many RPM) the edges of the guides break off like glass at the port side.

Thanks for the info..