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DIY Refurbishing of cylinder heads

After 4 attempts of having others redo my cylinder heads, and said refurbishings lasting anywhere from 1800 to 15000 miles, I decided to give it the old DIY try.

It was a long but fun process, and why not document it here. I am sure the pros have different / better methods, but I had no outside help and this worked for me.

First, the angles of the valves need to be divined. I placed the heads on a sine plate on my mill, and checked relative to some drill rod chucked in the spindle. As the heads had been reworked previously, and the guides were worn a little, I measured all heads and averaged the results.
Intake = 25.6 deg
Exhaust=30.28 deg

Then, time to measure the studs & alignment pins on the head. I don't have spare cam towers, nor is my little mill big enough for them, so I made my own fixtures for holding the heads.


I made 2 fixtures for holding the heads at the intake & exhaust angles and used the mill to remove the guides. First, a 1/2"carbide end mill plunged straight down to remove the valve stem seal part of the guide. Then, a 31/64 carbide drill to drill out most of the guide. Then just some drill rod to punch it out.
Probably a piloted drill would have been much easier ...

I did not find HSS to do very well cutting the manganese bronze guides.

One of the guides just spun in its hole ... and then came out with light taps of a hammer. Clearly not sized properly for its hole! In fact, none of the guides were!

I made another set of fixtures for holding the heads upside down and I bored a slightly deeper recess on the port side to clear the guide.




All the holes got measured to the neares .0005 & recorded. Hole diameter ranged from .513 to .517, with one outlier at .5325. That one started quite mangled from a loose valve guide - the reason for this refurbishing - so I bored it oversize.

New valve guides came from si valves. I ordered unfinished guides, as even the oversize ones were too small for the proper press fit in my heads.

A tapered arbor proved too flexible for accurate sizing of the guides, so I made one with a thread on the end to clamp the guide. 7/16 threads with the crests cut off to fit the 9mm guides worked well. There was plenty left to clamp the guide. Again HSS tooling didn't seem to work well, so I used carbide and light cuts between centers to keep things concentric. Lathe is a 1940's South Bend 9A. Guides were sized for a .0023 to .0028 press fit - that's as accurate as I could cut, and well within the allowable spec.



The grossly oversized guide bore needed a much larger guide. Fortunately a VW Type4 guide fits the bill. Here I am machining the valve stem seal grooves...



The fixture I used to hold the heads on the mill was of course far too tall to hold them on the arbor press, so a shorter one was made that could accommodate both intake and exhaust valves. The Bentley says to use tallow as a press-in lubricant, so that's what I did, and it worked like a charm. All the guides went in with little fuss. I made a piloted pin & a .520" thick spacer so the guides pressed in to the specified height. Prior work on my heads used the guide's small step as a stop, which mangled the upper .030"of the guide bore ... apparently not everyone uses a stop.



More in the next post ...
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Old 03-24-2018, 09:15 AM
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With all the guides pressed in, time to ream. I used a piloted 9mm HSS reamer for bronze guides from cylinderheadsupply.com with lots of oil, and it worked quite well, though it required a *lot* of force to turn it.



Resulting holes were just slightly under 9mm. The bore gets smaller after pressing the guides into the heads!

Valve clearances on 911 heads are handled by the valve stem sizing - the valve guides are all sized to the same diameter. So do not make the exhaust guides larger for added clearance - the exhaust valves have a smaller stem to take car of that!

Final sizing was with a 240 grit flex hone. The flex hone said 30 - 45 seconds of honing. Wanting to do an extra good job, and measuring the reamed hole at a little less than 9mm, I went 45-60 seconds. I did all the heads at once. Probably this is a rather obvious faux pas... and every one turned out .0015" too big.


All the guides got pressed out again, new ones were procured, the bores got measured, guides were sized, pressed in, and reamed.

Having experience, I used a spare guide to see how fast flex honing removed material (quite fast!) and adjusted my honing time to 10-15 seconds. This time around the fit was perfect.

A little shopmade gage checked for proper valve stem height.


The most expensive part of the job was the valve seat cutting. I bought a set of Neway seat cutters. They seemed to work OK - I did not have chatter issues, but they did require a lot of pressure to cut the seats, and it took quite a while for the ports to hold water with just finger pressure on the valves. They did all seep a little after 10 - 20 seconds. I did not lap the valves in - the Neway instructions said it was not necessary.



On to reassembly ...

I found a crack in one of the spring retainers! Looks like a notch from some rough handling in the past, progressing into a hairline crack maybe 3mm long.



I could not stand the generic valve spring compressor I'd been using, so I made my own. ACME threads at 10TPI make it quick & easy to use.



I also found I was short seat shims. Since I cut all the seats deeper, I needed more shims for all of them. And I cannot get myself to pay $3.50 + shipping for a dang washer. Also the Bentley spec calls for 1.358"+0 -.012" ... probably a misprint, but also rather difficult to achieve with .020"shims.

...
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Old 03-24-2018, 09:50 AM
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Having acquired a Chinese crap mill with CNC conversion, and having worked all the bugs out and gotten it running allright, I used it to cut some shims from .062 and .050 aluminum, replacing 3 or 2.5 shims, as required. Since it's CNC, why not engrave the thickness right on it. And I added a hole so I can fish them back out of the valve seat recess, since magnets work poorly on aluminum. There is considerable mass savings of maybe 1 or 2 ounces with this approach.



The 356-style valve spring height gage sold for 911 purposes looked like it could not possibly be accurate to .01 or even .02". I tried the wire with masking tape or wire with handle methods and found them entirely unsatisfying. The micrometers sold by Summit et al are all too tall for 911 usage ... so, like a good toolmaking monkey (left handed, retarded, etc), I made my own. It's calibrated in full & half shims. Just screw it in, add the retainer & keepers, and screw it out. It directly reads how many shims to add, and it even presses everything together so it's a good measurement.



I did double check every one after adding shims (using the same tool), and they all came out matching the Bentley spec.

Worked like a charm, and exceptionally satisfying to use!



Now all I need is for Winter to release its death grip on Michigan so I can yank the motor and replace the heads in time for the first track day in May ...
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Old 03-24-2018, 09:51 AM
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Very cool. I have been looking at those Neway kits for awhile, which one did you buy? I should have just bit the bullet a long time ago and bought one, it would have paid for itself by now.

Patent that spring height gauge and set up production..

Last edited by boosted79; 03-24-2018 at 12:08 PM..
Old 03-24-2018, 12:06 PM
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Very impressive.
The ultimate DIY motor job.
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Old 03-24-2018, 12:49 PM
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Awesome!!!
Old 03-24-2018, 01:09 PM
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Boosted, I just bought individual parts. T-handle, an expandable pilot, 1.5"and 2"cutters for 30, 45, and 75 (I think) degrees. The 30 & 45 are one cutter, 2 sides.

The sizes are less than ideal for the 30/45 cutters, but they do work (the carbide cutters can be shifted as needed). 2.25 or 2.5 would be better for the intakes, and 1.75 or 2" for the exhaust, I think.

For cost savings, one could probably get by with a 2"cutter and shift the carbide bits as needed.

I can make more of the spring height gage if there is actually interest. But its hardly patentable ... just an adaptation that works for the 911.

https://www.bing.com/images/search?q=summitracing+spring+height+gage+valve&FORM=HDRSC2
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Old 03-24-2018, 01:23 PM
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That's the spirit.

Although, TL;DR.

Will though when time permits. Love it.
Old 03-24-2018, 01:30 PM
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" But its hardly patentable ... just an adaptation that works for the 911."

Yeah, but I bet you could sell some on here. Tough to make any money at it unless you value your time at close to zero though.

Did you just buy new valves or have the old ones ground?
Old 03-24-2018, 03:00 PM
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I am impressed. Well done!!!!

The impressive part for me is that you actually measured the parts. This is the difference between production level work and precision level work.

One small addition here to note. When measuring the installed height of the valve spring, the retainer height, you are "setting" what is considered an easy way to install the spring installed seat pressures somewhere close to one another. The home DIY or the repair shop typically will not have a way to test each spring and set the installed pressures the same.

The fact that you actually measured the retainer heights was reassuring. Most don't and slam 5 shims under the spring base and "ship it".
Old 03-24-2018, 03:03 PM
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Last year I did mine in my garage as well.

One thing I did to avoid the weird angles of the valves was to us a press to push out the guides from the combustion chamber side. I did not have to make an angle fixture.

I supported the head with a large deep socket. I rested the head with the valve spring seat on the socket that was resting vertically on the bed of my press. That way I did not have to support the head with an angle fixture.

I also use the old VW method of removing the guides. That is, I used a 10mm tap to thread the old valve guide on the spring end. I inserted a 10mm bolt in the thread. I inserted a 1/4" drive socket extension through the guide to press it out with the force going on the bolt. The head were heated to around 350*.

All of the guide bores remained in new spec.

I used a Neway tool as well to do the seats.


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Old 03-24-2018, 03:31 PM
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"The head were heated to around 350*."

Yes, that is critical if you don't core out the guides.
Old 03-24-2018, 03:43 PM
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Very cool! Nice work!!!
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Old 03-24-2018, 04:53 PM
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Where’d you get the tallow? Any preference of beef over pork?


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Old 03-24-2018, 05:32 PM
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Really nice job, love it!!!

I remember not being happy with simply re-inserting the stack of stock shims, so made my own single piece shims as well; was a number of years ago now (that's how long my damn project has been running). I was fortunate to have access to a valve spring compressor rig, to measure the load for each spring. I then (as Neil mentions) made shims for each spring, surface grinding them from steel blanks I spun up on the lathe. We had a few that "let go" mid grinding and made a hell of a bang (magnetic bed wasn't *that* strong...we then took it even slower on the grinding steps, haha!
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Old 03-24-2018, 06:08 PM
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boosted, I ordered new valves. The old ones only had 18000 miles on them, but the seating surface was sufficiently worn that they'd need a light grinding to seat properly. Lacking proper equipment, I bought new (TRW).

Trackrash, good idea on guide removal! What did you do with the carbon crusties on the port side of the exhaust guides?

Craig, neither - I used mutton tallow. Available on fleabay as well as Lee Valley Tools. The fleabay stuff is sold as moisturizer, the Lee Valley version is for making hand planes glide over wood better than the traditional wax. I have not tried it in that capacity, but I will with the next woodworking project.

An invasion of flying saucer valve spring shims sounds entertaining as long as the flight path is not towards anything breakable
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Old 03-25-2018, 09:14 AM
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I cleaned out most of the carbon in the ports, especially around the end of the guide, before I removed them. A small wire brush helped. Probably could have done a better job, but my bores were still in spec after I removed the guides.

Interesting about the tallow lubricant. There was a thread about this a while back. I ended up using bacon grease. Later, I read in the Carrera workshop manual that Porsche changed to recommending talcum powder when installing the guides. Valve Guides

Also of note. I bought "standard" guides. Guess what? Not all of them were actually within standard spec. I had to machine several of them down to fit. Luckily I had bought extras just in case.
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Old 03-25-2018, 10:06 AM
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I was under the impression that the heads needed to be heated and the guides frozen before pressing into place ?
Old 03-27-2018, 03:46 PM
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Quote:
Originally Posted by Anglocanadian View Post
I was under the impression that the heads needed to be heated and the guides frozen before pressing into place ?
That's how I do it.
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Old 03-27-2018, 04:21 PM
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The Bentley does not mention heating or freezing for guides. It does mention heating the heads for seats.

I did not do any heating or freezing and the guides went in without any problems or undue force. Due to my honing faux pas, I even repeated the process - there was no galling or other damage to the guide bores. The mutton tallow does a great job!

Heating the heads to 350degF will make the press fit less by around .0018". I did consider going that route but thought I'd see how much force was needed to press the guides in cold, and they pressed in without protest.
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Old 03-28-2018, 05:58 AM
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