The problem with surfacing a head on a plate

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comnoz

comnoz

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I would not say it is impossible to get a good surface on a head by using abrasives on a flat plate. The abrasive needs to be stretched tight and solidly adhered to the plate. The heads I receive show that most of them are not done well enough.

Here are pictures of two heads I did today and one from a couple weeks ago. They had all previously been surfaced on a flat plate and looked great.

These pictures were taken after the initial .005" cut on the mill. Note how the abrasive sheets had made contact with the surface without actually making the surface flat. It just made the thin sections "low".
It's no wonder a lot of Nortons have excessive blowby and head gasket failures. Jim

The problem with surfacing a head on a plate


The problem with surfacing a head on a plate


The problem with surfacing a head on a plate
 
comnoz said:
Note how the abrasive sheets had made contact with the surface without actually making the surface flat. It just made the thin sections "low".
Click to expand...

Are we sure that this is not from the heads natural inclination to bow a little from being torqued down ??
 
Jim – I just pulled my RH10 head last night, and see a similar blowby pattern - between the cylinders and between the cylinders and pushrod tunnels. I am assuming that it is fairly common?

I am pretty sure that my head was never sanded on a flat, and my friend who milled the exhaust ports for me in the 90s did not mill the bottom face of the head.

BTW - how much do you need to skim off normally to fix this type of issue?
 
gortnipper said:
Jim – I just pulled my RH10 head last night, and see a similar blowby pattern - between the cylinders and between the cylinders and pushrod tunnels. I am assuming that it is fairly common?

I am pretty sure that my head was never sanded on a flat, and my friend who milled the exhaust ports for me in the 90s did not mill the bottom face of the head.

BTW - how much do you need to skim off normally to fix this type of issue?
Click to expand...


I am sure a lot of it is from the tendency for the head to warp in this pattern.

The problem is, it is hard to get rid of this by using abrasives unless the abrasive is really flat and firmly mounted so it can't move into the low spots. When that happens it just makes it look straight.

I usually end up somewhere between .004 and .010 to make them straight with the mill.

Sometimes if they have been run for a while with a pulled head stud it can take a lot more to make them flat again. Jim
 
So you're saying I shouldn't flatten my headed by rubbing it on the garage floor? :mrgreen:
 
swooshdave said:
So you're saying I shouldn't flatten my headed by rubbing it on the garage floor? :mrgreen:
Click to expand...

Naw, I would suggest a good old time barber. There is still a few around that can give a good crew....
 
Did the CF Bedford's Iron Head at the roadside , lapping it with corse & medium paste on the Side Window . :shock: :lol:
Gave Up before id got about 30 thou off , still a bit ' up ' on No 3 Ex Side . No water passage there ,
Went about a year later . Funny Chuff I couldnt Trace at the Ex Manifold .
It was spitting the gasket out .

Did the Falcon Alloy Head the other week . Train Window . ( A regect - replaced )
Gave up after a while and took a file to it before I ran out of lapping paste .
Id left the rad cap loose these last few years .
The laden Nullabor & Return etc trip got the olde ' alloy on Iron ' weeping ,
Original Gasket was still in there , most of the end Cyl ' flame rings ' were blown out , by the time I got around to it . :oops:

One Should check it with blue , on a flat plate . So they tell me . I used a straight edge . The multi Cyl heads can ' bow ' .
with a ohc with fixed cam bearings this can be a bother . Mines the olde push rod job .
 
swooshdave said:
So you're saying I shouldn't flatten my headed by rubbing it on the garage floor? :mrgreen:
Click to expand...

Garage floors are only precise enough for clutch plates. For total accuracy on a head I prefer a wood rasp duct taped to a 6 foot spirit level. One man on each end and a sharp eye on the level and your good! :mrgreen:
On a serious note though Jim-on a badly warped/distorted head how do you index it in the mill or surface grinder so as not to cut it at an angle? Take muiltiple measurements off the quill, split the difference and then raise the work into the cutter? Just something I've always wondered about.
 
MikeG said:
swooshdave said:
So you're saying I shouldn't flatten my headed by rubbing it on the garage floor? :mrgreen:
Click to expand...

Garage floors are only precise enough for clutch plates. For total accuracy on a head I prefer a wood rasp duct taped to a 6 foot spirit level. One man on each end and a sharp eye on the level and your good! :mrgreen:
On a serious note though Jim-on a badly warped/distorted head how do you index it in the mill or surface grinder so as not to cut it at an angle? Take muiltiple measurements off the quill, split the difference and then raise the work into the cutter? Just something I've always wondered about.
Click to expand...

That's the time consuming part.

First I compare the depth of the squish band counterbore on both sides. They should be the same depth all around unless the head has previously been milled at an angle. [another common malady]

If they are the same on both sides, I bolt the head down to my fixture -right side up.
I then mill a few thou from the three headsteady mounting pads to make them parallel with the head surface.

If the squish bands are not the same on both sides -I fit a precision ring in each chamber that locates on the squish band before I bolt the head down. Then when I mill the pads they will be parallel with the squish bands.

If the squish depths are way off, I call the customer and find out if he wants a big cut on his head to true things up or if he would rather live with unequal chambers and just a cleanup cut. A big cut may mean installing a de-compression spacer under the barrel.

Then I turn the head over and bolt it to my fixture with the 3 headsteady mounting holes.
I have an adjustable bracket that mounts between the fixture and the intake flange to keep the head solid while I mill it. Jim
 
Well...

That explains why my squish band clearance measurements came out better after Jim skimmed my head, even if only lightly.

Its that attention to detail (that's just done as a normal part of the job without any fuss) that sets folk like you apart Jim.
 
The same topic comes up with Vincent heads, the question being "is it best to machine or fit for a seal?"
The machinist's point of view is that the finish from from milling or turning can be finer than from fitting ( grinding paste) and is almost always flatter.
With Vincent heads, there is no gasket, so the fit is critical. The long accepted method of achieving a seal is to put grinding paste in the head to cylinder joint then work the head back and forth until everything is matched up.
The Machinist says these jointed heads are very irregular when milled to correct, just like the Norton head above which Jim flattened and fixed.
When it is suggested that after milling, the head should be final fitted via the grinding paste method, the Machinist says "why mess up a nice, flat, machined x? Micron finish that my mill produces?"

Proof is in the pudding, the machinist's bike set the fastest time out of approximately 90 roadgoing Vincents run at the Ramsey Sprint 1999, then again in 2007.

Glen
 
Yeah, I have tried running a Norton without a head gasket.

I could get a perfect seal -until the first time it got good and hot....

Then they leaked compression into the pushrod tunnels. Jim
 
The trouble is those danged alloy heads turn into a pretzel when they get hot.
If only they'd stuck with iron....
 
I never found a sheet of sandpaper big enough to surface a head and never trusted the results. And how about the cast iron cylinders? I have found that cylinders that have never been surfaced are usually out by about .004. Any experience in this dept?

MR. COMNOZ.... while I am here perhaps you can give some advice on my current problem. I have a loose bearing in a Goldstar case, drive side, the outermost. The machinist I usually go to says give the case a light knurl and install the bearing. I would like to plate the bearing and LIGHTLY bore the bearing hole to fit. A really big problem is that there is very little material in the case to machine away, otherwise sleeving the bearing would be a good option. Any ideas? And how thick a plating can I get? I would like .002 on each side, total .004 increase on the O.D.
 
MikeG said:
swooshdave said:
So you're saying I shouldn't flatten my headed by rubbing it on the garage floor? :mrgreen:
Click to expand...

Garage floors are only precise enough for clutch plates. For total accuracy on a head I prefer a wood rasp duct taped to a 6 foot spirit level. One man on each end and a sharp eye on the level and your good!
Click to expand...

I needed a good laugh. Thanks for that.
Hang on though.......it just might work......... :idea:
 
seattle##gs said:
I never found a sheet of sandpaper big enough to surface a head and never trusted the results. And how about the cast iron cylinders? I have found that cylinders that have never been surfaced are usually out by about .004. Any experience in this dept?

MR. COMNOZ.... while I am here perhaps you can give some advice on my current problem. I have a loose bearing in a Goldstar case, drive side, the outermost. The machinist I usually go to says give the case a light knurl and install the bearing. I would like to plate the bearing and LIGHTLY bore the bearing hole to fit. A really big problem is that there is very little material in the case to machine away, otherwise sleeving the bearing would be a good option. Any ideas? And how thick a plating can I get? I would like .002 on each side, total .004 increase on the O.D.
Click to expand...

I have never tried to plate a bearing. It would be pretty tricky since any plating solution that got into the bearing would destroy it.
I have made and installed bronze bushings with wall thickness in the range of .030 -.040 with good results. It's a slow and tedious job -but may save your case. Jim
 
seattle##gs said:
I never found a sheet of sandpaper big enough to surface a head and never trusted the results. And how about the cast iron cylinders? I have found that cylinders that have never been surfaced are usually out by about .004. Any experience in this dept?

MR. COMNOZ.... while I am here perhaps you can give some advice on my current problem. I have a loose bearing in a Goldstar case, drive side, the outermost. The machinist I usually go to says give the case a light knurl and install the bearing. I would like to plate the bearing and LIGHTLY bore the bearing hole to fit. A really big problem is that there is very little material in the case to machine away, otherwise sleeving the bearing would be a good option. Any ideas? And how thick a plating can I get? I would like .002 on each side, total .004 increase on the O.D.
Click to expand...

I have bought emory cloth as large as 36 inches by 72 inches from 3M. It is available but costs more than a mill job.

Abrasive liquid and powder are also available -but you really need a flat surface that is softer than the aluminum head to use it effectively. Jim
 
I have copper plated Commando main bearing inner races, and it is as Jim says, you have to be very careful to mask the bearing surface, or it will also get plated. I twisted a wire around the removal groove in the race to get a ground connection, then dipped the whole thing in wax, and trimmed away the wax where I wanted the plating. I learned the hard way some years ago that you need to use a soft enough wax that it doesn't chip and crack when trimming it away. Any little crack will lead to plating on the bearing surface. A mix of bees wax and paraffin works pretty well. .002" thick plating is pretty easy to do. You just have to pull it out of the bath and measure it until it's thick enough. I use a Caswell plating kit.

That's for just the race. If I were trying to plate just the outside of a complete ball or roller bearing, I'd really worry about how to keep it sealed from the plating solution.

If it was me, I'd go with Jim's idea of a very thin bronze insert, bored to size.

Ken
 
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