Duetto engine removal - Page 7 - Alfa Romeo Bulletin Board & Forums
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post #91 of 197 (permalink) Old 02-06-2019, 04:13 PM
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Collets get mushroomed by the valve shims. This happens when a machine shop surfaces the tops of the valve stem. Which is a common practice on most other engines because the top of the stem gets worn from the rocker pushing on it.
It is also common practice on Alfa engines worked on by shops not familiar with Alfas. The problem is that the tappet-to-cam clearances must fall within the range that can be adjusted with off-the-shelf shims. Often the shop will set the valves too deep in their seats, resulting in such tight clearance that even the smallest available shim won't give sufficient clearance. You can sometimes solve this by grinding the shims even thinner, but more commonly, a naive shop will just grind down the valve top and figure they've solved it. Putting in a new valve seat is the proper solution, but that would cost more.

The point of all this is that there are a number of machining operations that are different on Alfas - particularly on the heads. Every shop says "well, shucks, if we can machine Chevy V8's for drag racing, we can machine some little Alpha Romero. But often they just can't,

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'67 Duetto
'91 164L
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post #92 of 197 (permalink) Old 02-06-2019, 06:51 PM Thread Starter
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It is also common practice on Alfa engines worked on by shops not familiar with Alfas. The problem is that the tappet-to-cam clearances must fall within the range that can be adjusted with off-the-shelf shims. Often the shop will set the valves too deep in their seats, resulting in such tight clearance that even the smallest available shim won't give sufficient clearance. You can sometimes solve this by grinding the shims even thinner, but more commonly, a naive shop will just grind down the valve top and figure they've solved it. Putting in a new valve seat is the proper solution, but that would cost more.

The point of all this is that there are a number of machining operations that are different on Alfas - particularly on the heads. Every shop says "well, shucks, if we can machine Chevy V8's for drag racing, we can machine some little Alpha Romero. But often they just can't,
That's funny! My shop say's they're experienced with Alfa's but I'll pass these pieces of advice on to them😊.
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post #93 of 197 (permalink) Old 02-06-2019, 10:01 PM
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If the valve shim is striking the collet hard enough to mushroom it, wouldn't that be making noise? Is the shim also damaged as a result?

-Kevin
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post #94 of 197 (permalink) Old 02-06-2019, 10:32 PM
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The shim is actually being held up from resting on the stem head because it is resting on the collet. 2 things will happen. First the shim will start to damage the collet. Then the shim will eventually shatter causing running issues and will usually damage the valve cup.

You won't hear any noise until the shim actually breaks.

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post #95 of 197 (permalink) Old 02-06-2019, 10:37 PM
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The shim is actually being held up from resting on the stem head because it is resting on the collet. 2 things will happen. First the shim will start to damage the collet. Then the shim will eventually shatter causing running issues and will usually damage the valve cup.

You won't hear any noise until the shim actually breaks.
Ok, makes sense. I was having trouble visualizing it.

-Kevin
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post #96 of 197 (permalink) Old 02-08-2019, 06:08 AM Thread Starter
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"It is also common practice on Alfa engines worked on by shops not familiar with Alfas. The problem is that the tappet-to-cam clearances must fall within the range that can be adjusted with off-the-shelf shims. Often the shop will set the valves too deep in their seats, resulting in such tight clearance that even the smallest available shim won't give sufficient clearance. You can sometimes solve this by grinding the shims even thinner, but more commonly, a naive shop will just grind down the valve top and figure they've solved it. Putting in a new valve seat is the proper solution, but that would cost more."

So I'm waiting to hear back from my machine shop, who are putting together a quote for the work they need to do, and thinking about what Jay said about the valve seats. My shop didn't mention needing to replace the seats, but noted the mushrooming....do you guys think I should tell them to replace the seats as well?
Thanks for your collective input! I really don't have much experience with machining. I just drop stuff off and tell 'em to call me when it's done😀.
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Mark
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post #97 of 197 (permalink) Old 02-08-2019, 07:26 AM
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My shop didn't mention needing to replace the seats, but noted the mushrooming....do you guys think I should tell them to replace the seats as well?
I'm not saying that you always need to replace the valve seats. Your's may just need to be cleaned up, as long as they can do this without positioning the valve too deep in the head.

What I am saying is that the depth of the seat, the length of the valve and the type of cam you are using will all influence the final valve stem to cam clearance. And, that clearance must be within a range that can be adjusted with available shims.

So one solution is to make the shop responsible for adjusting the cam-tappet clearances. They'll need your cams and should have a full set of shims since they are an Alfa-experienced shop. But verify the clearances before accepting the head and make them promise not to grind the valve stems to the point where the shims are resting on the collets.

The other solution is to instruct them to make sure the valves are in the range that can be adjusted, and then set the final clearances yourself.

Jay Mackro
San Juan Capistrano, CA

'65 Guilia Sprint GT
'67 Duetto
'91 164L

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post #98 of 197 (permalink) Old 02-08-2019, 08:15 AM Thread Starter
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I'm not saying that you always need to replace the valve seats. Your's may just need to be cleaned up, as long as they can do this without positioning the valve too deep in the head.

What I am saying is that the depth of the seat, the length of the valve and the type of cam you are using will all influence the final valve stem to cam clearance. And, that clearance must be within a range that can be adjusted with available shims.

So one solution is to make the shop responsible for adjusting the cam-tappet clearances. They'll need your cams and should have a full set of shims since they are an Alfa-experienced shop. But verify the clearances before accepting the head and make them promise not to grind the valve stems to the point where the shims are resting on the collets.

The other solution is to instruct them to make sure the valves are in the range that can be adjusted, and then set the final clearances yourself.
i'm just going to print all this up and take it into the shop . i was planning on doing the final clearances myself, but in light of all this new information, i may have them do it if they can't guarantee me i won't run into this "potential" problem.
thanks for clarifying!
mark
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post #99 of 197 (permalink) Old 02-08-2019, 10:24 AM
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i was planning on doing the final clearances myself, but in light of all this new information, i may have them do it if they can't guarantee me i won't run into this "potential" problem.
Just to confuse you further:

- There are a lot of advantages in setting the valve clearances yourself. You will do a more precise job than the 20-year old helper in the machine shop, who is listening to rap through his earbuds while working on your head.

- Unless you have access to a selection of shims, setting the clearances precisely can drive you nuts. The shims come in .025mm variations, from 1.3 - 3.5mm. You find yourself measuring the gap, figuring that you need a 1.025mm shim (say) order that one, it arrives a week later, you install it, measure the gap and immediately say "oh &%$#@, I should have gotten 1.050mm!". Now that car will still run with the clearance .025 off; it'll just drive you nuts.

- Maybe the best solution is to have the shop take the first pass, and then you clean up the job that 20-year old helper did.

Jay Mackro
San Juan Capistrano, CA

'65 Guilia Sprint GT
'67 Duetto
'91 164L
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post #100 of 197 (permalink) Old 02-08-2019, 12:32 PM
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When you estimate a shim size, order a few sizes around that. Yes, you will end up with a bunch of extra shims. I did this for several years, and have ended up with a LOT of shims. Finally I can do any adjustment I need. I was even able to sort them into half sizes by carefully measuring, and even made a case to hold them. See attached photos. This is the standard range of shims; there is also a set of larger sums, which is on the reverse side of the holder. You can also occasionally find a bunch of shims on eBay.

Note that in the second pic, there are some wooden plugs that show which shim is currently installed.

Robert
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post #101 of 197 (permalink) Old 02-08-2019, 12:47 PM
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post #102 of 197 (permalink) Old 02-08-2019, 01:02 PM
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When you estimate a shim size, order a few sizes around that. Yes, you will end up with a bunch of extra shims. I did this for several years, and have ended up with a LOT of shims.
Yup, that's the right way to do it.

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'65 Guilia Sprint GT
'67 Duetto
'91 164L
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post #103 of 197 (permalink) Old 02-08-2019, 01:02 PM
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BTW - in order to sort to half sizes, you really need to be able to measure 1/10,000 repeatedly. You also need a very high quality micrometer. Dial gauge thingies will not do. Also, an older Starrett (or other top quality brand) gauge measures more consistently than a new one. I got mine from my dad, who got it from his dad. It's the years of repeatedly turning the barrel that smooths out any variations in the threads, so it gets more consistent with time. Look for one at your local flea markets!

After getting several different measurements for each shim, you will develop a consistent touch in using your micrometer. That's what it will take to sort the shims. Also, you need the same touch in measuring the engine's gaps to choose by half-sizes. A little practice will go a long way.

Robert
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post #104 of 197 (permalink) Old 02-08-2019, 01:27 PM Thread Starter
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wow! you guys are hardcore! so my first valve adjustment should cost ~$200 in shims?
i like your shim selection sorter Robert.
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post #105 of 197 (permalink) Old 02-08-2019, 02:33 PM
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wow! you guys are hardcore! so my first valve adjustment should cost ~$200 in shims?
Well yea, but your shim set becomes an heirloom that you can pass down to your heirs. Think of how overjoyed the will be!

Jay Mackro
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'65 Guilia Sprint GT
'67 Duetto
'91 164L
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