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Discussion Starter #1
I recently got my cylinder head back from the machine shop, and it looks like they did a pretty good job. The seats were cut, the valves lapped in, and .005 inches shaved from the head surface to clean it up. Now, for some reason, the tappet cups won't fit back smoothly in the bores in the head. They bind up badly, and no amount of lubrication seems to help. The head was glass-beaded as part of the valve job, and may be the reason for this problem. Is it possible that the bore was "roughed up" by the glass beading and this is why the cups won't slip back in easily? Has anyone else had this problem after having their cylinder head machined? I'm considering using a cylinder hone to try to smooth out the interior surface of the bores so that the cups will go back in smoothly.

As usual, any help would be greatly appreciated and insure your eternal happiness in the afterlife.
 

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when bead/glass blasting they would have hopefully protected and internal bores I would have thought! They cant be that nuts!

When you took out the tappet cups did you mark which cup came from which bore?... as they have to go back into the exact same bores they came from....
 

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Discussion Starter #4
I would also have assumed that the machine shop would not have glass-beaded the bores, and I can't visually determine if they did. I haven't spoken to them, but the shop has a good reputation. I just don't know what else it could be.
I did carefully mark which cup came from which bore, so that's not an issue. Any opinion on using a cylinder hone to smooth out the bores?
 

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Depending on what media they used for blasting, you could have serious trouble as many will imbed in aluminum. Too high air pressure, or incorrect media will leave aluminum like an abrasive, and not much you can do gets the stuff out.
As a rule, NO media inside an engine is a good rule.
There are exceptions, soda blasting washes off with water, Co2 blasting evaporates and so on.
 

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Discussion Starter #6
Thanks Gordon,

You make an excellent point. I've run my finger around inside of the bores and they feel pretty smooth which, of course, given the nature of the problem, really doesn't mean anything. We're probably dealing in thousandths of an inch here, so I'm still giving strong consideration to using a cylinder hone or similar device to put a smoother finish on the bores. I'm going to give the machine shop a call first thing tomorrow morning and follow up on what they did and how they did it.
 

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I recently had an issue installing a new exhaust tappet in an V6 engine. I used a piece of fine emory cloth on the tappet and it went in fine. I checked after about 25 miles and it was rotating like it was supposed to. Just another idea.

Michael Conrey
Smithsburg, MD
 

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If you are going to polish the bores, instead of fine emery paper, use crocus paper. It is much finer and the machine shop should have some.
 

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Discussion Starter #10
Hi Eric,

Four of the cam bearing journals are still shiny, but the remaining two are questionable. Looks like I'm going to be doing a lot of polishing of bores. I'm very disappointed in the machine shop, but there's not much that can be done about that now. Tough lesson.
 

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Discussion Starter #11
I just went down and checked the lower cam bearings on the head against the upper ones which were removed prior to the head being sent out. They seem identical, so maybe I dodged that bullet. I slso double-checked the fit of the tappets; most of them begin to bind up as soon as they're inserted, or about a third of the way in. I'm going to call the machine shop tomorrow and try to find out exactly what they did, and why. I'm more likely to take the time to polish the bores myself with crocus cloth than depend on them to do it after seeing their work. These guys do some very involved custom work on performance heads, which I would assume includes aluminum ones, so how could they screw my head up so badly (rhetorical question, I know?

Thanks for all of your helpful suggestions. Time for a drink.
 

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Was any other work done to the head? Installing new guides, for instance? When you are working around the bores for the cups, it isn't hard to mar the surface, creating a burr that will prevent the cup from going in. Crocus cloth or something similar is the way to smooth out such burrs.

Gordon Raymond said:
Depending on what media they used for blasting, you could have serious trouble as many will imbed in aluminum.
Yea, that's what I have always been told (of course, I was probably told it on the BB by Gordon). The worry is that the media will embed into the aluminum, and then come loose with exposure to oil and heat. And, abrasive media inside your engine is bad news. It might be worth asking the machine shop what media they used.
 

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Discussion Starter #13
Great suggestion Jay! Should be an interesting phone call. And it does kind of feel like burrs are the problem. I'll post when I get that information; might help someone in the future.
 

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Discussion Starter #14
Well, I found out the sequence of events leading to this problem. I had brought the cylinder head to the machine shop bare; no cams, tappets, shims, etc. Had those items been there, they would have honed the bores out and put the tappets back in. Since they weren't, they felt no hesitation in glass-beading the head (bores included) and returning it to me in its present condition. As far as I'm concerned, this is total BS, and just an excuse to cover up a half-assed job. The media they blasted with was glass, so I'm going to hone the bores out with a brake cylinder hone and light oil, then follow up with a solvent wipe.
Guess the old adage is true; "experience is what you get when you don't get what you want".

Thanks for everyone's help.
 

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sure sounds like BS to me too! glass beading internal bores!
They could have at least tried and keep you as a customer and have offered do the honing for you.

Hope it goes well for you and they haven't done irrepairable damage to something like guides, valve seats or even spark plug threads in the head:(
 

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Discussion Starter #16
They actually offered to do the honing for me but, based on what I've seen so far, I elected to do the work myself. What with removing and re-installing 8 valve springs and retainers, the whole project will probably consume a few hours, but at least I'll know that everything fits well. The valve guides were not replaced, but they did cut the valve seats and lapped the valves in (there's still traces of Prussian Blue attesting to this). The spark plug threads seem to be fine.
I guess you have to be really specific when ordering work to be done on these heads, and not assume that the people doing the work are as experienced as they think they are.
 

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What a shame. A machine shop that will glass bead a machined surface. Yikes! What has happened to craftsmanship? They probably gave it to a 14 year old to clean up and never looked. I would ask for my money back.
 

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....but they did cut the valve seats and lapped the valves in.
If the valve seats have been cut, but the valve stems are still their original lengths, you may find that the cup-to-cam clearance is too small for a stock sized shim to work. In other words, the valves have been shifted upward, and if your shims were already toward the thin end of the range, the clearance may now be too tight for any shim to fit.

Not to give you one more thing to worry about, but I have run into this problem in the past. If the clearance is close to accepting the minimum thickness shim, a competent machinist can simply grind a bit off the tip of the valve stem. In more extreme cases, new seats need to be fitted.
 

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Discussion Starter #19
I don't know why they would glass bead a machined surface either, but at least the surface of the head is fine. They told me that had I given them the head with the cams in place, they would have cleaned up the tappet bores and re-assembled it. I guess its somehow my fault for trying to make their job easier by stripping the head myself (under the heading of "no good deed goes unpunished".

With regard to the cutting of the valve seats, my understanding is that they only as needed to correct some pitting but, as you pointed out, at this point I don't know how much they took off. As I recall, most of my shims and clearances seemed to be in the mid-range, so maybe I'll luck out on this aspect of the project. Lord knows I could use a break.
 

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In theory, Alfa valve seats have a taper to them, the largest O.D. being the part deepest in the aluminum. The whole seat is a heat transfer assembly, to the aluminum and to the coolant.
After the seat has been cut enough to be below the surface of the surrounding aluminum, both it's heat transfer, and hold in the aluminum are reduced. The "shielding" of the valve, lowered in the pocket will effect breathing in performance engines.
Done correctly, all seats are cut to the same depth. All valve stems to the same length. Assembled, this should put the clearance in the mid-range of the lash caps available for adjustment, ASSUMING the bottom circle of the cam has not been reground as the cams were re-profiled. IF the bottom circles were reground, a slightly longer stem restores original geometry, without the need for really thick lash caps.
Unfortunately, many "in-and-out" head rebuilds consist of little more than removing enough material from the seats to clean-them-up, leaving them at different depths. They may, or may not, cut valve stem tips, often leaving lash caps to seat on the stem lock, rather than the tip. This is BAD practice!
One reason I often mention the use of a shop that specializes in aluminum heads is milling of those heads rather than hydraulically pressing them flat. The other is a properly done valve job.
Short cuts will give you a job that may work for a while, but usually about 1/3 the service life of the same job done correctly.
From my experience.
 
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