View Full Version : Valve seat cutting tool

Paddy O'S
12-16-2005, 06:37 AM
Has anyone made a valve seat cutting tool ? Reason I'm asking is that I've just replaced the valve guides on my Honda CBX 750 and now find that the valves are not aligned with the seats, too much for hand regrinding. The most commonly availabe cutter seems to be the Neway which has angled cutter heads with carbide insert cutting blades, downside is that these tools are pretty expensive for occasional use. It should be possible to make the angled cutter heads and pilots but I'm looking for ideas on what type of inserts to use and a method of accurately locating them on the cutter head, or indeed any other ideas or designs anyone may have used.
Thanks in advance / Paddy.

12-16-2005, 09:40 AM
Couldn't you just take it to a shop that does this?

But on the other hand you would be able to do three angle valve jobs on virtually any small engine.

[This message has been edited by topct (edited 12-16-2005).]

12-16-2005, 01:18 PM
I have an old valve grinding rig made by Black & Decker. They (at least used to) make professionally quality equipment for this. It uses a 90* drive electric 'drill' that drives an adapter that takes pre-shaped grinding stones. The ones I have are 30*, 45* and 60*. The whole thing gets centered up by a close fitting stem that goes in the valve guide.

It works really well on both CI and the hardened inserts. Still working on my stock of old stones, but was told they are available through GOOD quality auto parts stores. It wouldn't be hard to make up an adapter and stem to accept the stones.


Be careful what you wish for, you might just get it!

[This message has been edited by Ausserdog (edited 12-16-2005).]

12-16-2005, 02:40 PM
A valve seat grinder, as Ausserdog described, is the only way to go. Even if you use a cutter, you will still need to grind the seats before any hand lapping. You won't need much if any hand lapping with a well done grind job.

12-16-2005, 10:45 PM
Yes,I've cut valve seats.You can cut hardened seats with carbide.But you will have to grind the valve.Will try to hunt up the tool and post a pic tomorrow.It's a relativly easy tool to make.I've never lapped a valve seat after I cut it.I do blue up the valve and check it.I prefer to let the valves wear in.I'm afraid of lapping compound imbeding and causing faster wear.

12-16-2005, 11:02 PM
Hi There,

You can find a lot of auto rebuilding supplies and tools at Goodson Tools and Supplies. They carry stones, pilots, drivers, etc.


Good Luck!
-Blue Chips-

[This message has been edited by WLW-19958 (edited 12-16-2005).]

12-17-2005, 12:23 AM
<font face="Verdana, Arial" size="2">Even if you use a cutter, you will still need to grind the seats before any hand lapping.</font>

You must use worn out grinders and cutters. I've never had to even lap valves after using my cutters. The finished surfaces look like chrome.

12-18-2005, 12:12 AM
I suggest you listen to CCWKEN, there is nat a professional race engine builder in the country that would let you near his heads with a grinder or valve grinding compound. Properly used a seat cutter is as good as it gets. And they don't grind valves either, they use new ones.Done correctly the seating area is 10 thou. wide.

12-18-2005, 01:48 AM
I'll admit I haven't done a set of heads in a long time. I used to do three angle seats using a grinder for the seat and top angle. Then I would lightly lap the seat to define exactly were the seat was and then used a cutter to form the bottom angle and to narrow the seat and to make sure the seat width was even all the way around. The cutter we had used a single cutting edge and did not have a positive way of controlling the down feed as you turned it, That's why I didn't use it to cut a finished seat.I always had good luck doing heads this way and never had a set come back for any reason. As far as I can tell, a valve that seats well is good to go no matter what method was used to accomplish the job. As far as using new valves, unless they grew on trees, somebody ground the seating surface on them. On high performance heads, after I lapped the seat as I stated above, I would cut a second angle on the valve under the lap line to open up the valve area at low valve lift and to lighten the valve somewhat. If you wanted a .010 wide seating area, all you had to do was grind the seat one degree steeper than the valve face and you would achieve a very narrow seat. I always felt a carefully narrowed seat at the same angle as the valve lasted longer and seated better.

12-18-2005, 04:46 AM
Lapping of valve seats is a waste of time if you have machined the seat and valve as the contact area will change once the engine is warm.
Goodsons does make a three angle cutter that works well. Don't for forget about the interference angle.

Norman Atkinson
12-18-2005, 06:51 AM
I confess to have dealt with dozens of valve seats on cast iron British "A" series heads.

Having regard to all the comments, I would dismiss the 10thous theory business out of hand. I have always series cut the heads to obtain the best gas flow, in and out. I have always blued in- after grinding. There is a point in which a continuous ring of contact which happens. At that juncture,
the seal is complete. After re-assembly, the valves will hammer down to produce a wider seal. If one thinks about it, valves should always be re-gapped after re-building.

I could go on about balancing combustion chambers with burettes full of oil and stop watches timing flows of water after gas flowing and all that lark. Doing valve seats is the easy bit!

I am sure that those with ingrained cast iron and carbon in their finger nails would agree.


12-18-2005, 08:26 PM
Paddy, you might want to be careful with your Honda's valves (no lapping) as Honda valves from the early "80's on have a somewhat thin coating that if lapped off will facilitate rapid valve wear(burnt valves) ..... don't ask how I know,all I'll say is it was an expensive lesson. And the nu-way cutters are the cat's a$$ for doing the occasional valve job, my set was stolen, along with a friends Suburban that was never recoverd, so he bought me some of the replacement carbide inserts ,and I have made my own holders and pilots.Have experimented with a steel body,and a standard carbide insert that was soldered in a slot .200" wide and ground for relief on the back edge that has worked pretty good on the tractor seats I am cutting now.The carbide inserts from Goodway for the Nu-way are a little pricey, so I am getting ready to look for some smaller carbide bits,and do some more holders for different angles/valve sizes. good luck Shawn

Paddy O'S
12-19-2005, 02:58 PM
Thanks for all the input. I was certainly thinking along the same lines as Shawn, I have ordered some cabide tool bits which are 3/32" square which should work as described by Shawn. Another point is that that the CBX 750 ( Nighthawk in the US ) uses hydraulic tappets so I think I may have to grind a couple of thou off the valve stems so that the tappets won't lock up and hold the valves slightly open all the time.
Thanks again / Paddy.

12-19-2005, 05:28 PM
Paddy, I would not grind anything off the ends of the stems. I think there is a procedure for reinstalling the hydraulic followers. It should be in the manual.

I may mistaken, however I do know for sure that on certain of there models a definate procedure is neccasary to make sure that they will work correctly.