Engine Seized? - Page 18 - Alfa Romeo Bulletin Board & Forums
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post #256 of 572 (permalink) Old 10-31-2017, 06:08 AM
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Question What??

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Originally Posted by Jim G View Post
On the airflow meter, on top by where the rubber hose is connected there is a round aluminum plug. If it is smooth on top. If its been adjusted before it will already have one or two holes in it. Drill 2 1/8 inch holes, about an 1/8inch deep so you can pull it straight up with a pair of needle nose pliers. Underneath is an allen screw. This is what you use to adjust it. Unplug the O2 sensor and using a AFI meter set it to around 1-1/2 percent. There are conversion charts on the internet you can print out. After its set plug the O2 sensor back in. If the value on the meter drops the sensor works. If it doesn't its not working. It doesn't really matter if it is or isn't working unless you need to pass emissions.

This factory manual also tells you how to do this.
I am going to show my ignorance here, but I love to learn new things, about anything. The Alfa manual shows a meter being used, which reminds me of my old vacuum meter that I used to set the air flows on SU carbs. Is the AFI meter a more accurate vacuum meter? Second, 1 1/2 percent of what, idle compared to max air flow? What is the stock factory percent?

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post #257 of 572 (permalink) Old 10-31-2017, 08:55 AM Thread Starter
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I'm thinking ahead a bit here, regarding valve shims.

I've kept everything bagged and labelled. I have the valves, springs, tappets, shims, etc. for each valve.

My question is: if I install different valves, will I have to re-shim them? Is the purpose of shims to compensate for valve stem length variations, or for differences in valve seat placement? I'm not replacing or resurfacing the seats, just lapping the valves.

I've read through several threads regarding shims, but I'm confused regarding how the measurements are taken, and how the required shim size is calculated.

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post #258 of 572 (permalink) Old 10-31-2017, 08:57 AM
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Yes you will need different shims. Its really easy to calculate once you have done one. Measure the gap, and add shim thickness if the gap is too large, remove if too small. Its a bit trial and error but not difficult

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post #259 of 572 (permalink) Old 10-31-2017, 08:59 AM Thread Starter
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Yes you will need different shims. Its really easy to calculate once you have done one. Measure the gap, and add shim thickness if the gap is too large, remove if too small. Its a bit trial and error but not difficult
What gap?

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post #260 of 572 (permalink) Old 10-31-2017, 09:01 AM
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gap between the cam circle and the top of the cam follower. Put the cams so that the lobe is straight up, and measure with feeler gauge the gap between the cam and the top of the follower. The shims under the follower adjust that gap

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post #261 of 572 (permalink) Old 10-31-2017, 09:11 AM
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I'm not replacing or resurfacing the seats, just lapping the valves.

.
Putting new valves against old seats is poor practice. When an engine is down this far for a rebuild the head should be also be rebuilt.
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post #262 of 572 (permalink) Old 10-31-2017, 11:06 AM
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Quote:
Putting new valves against old seats is poor practice. When an engine is down this far for a rebuild the head should be also be rebuilt.
WHAT? You are proposing replacement of the valve seats? Do you know anyone who can that job? It is common practice to replace vales and just re-cut or grind the seats.

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post #263 of 572 (permalink) Old 10-31-2017, 11:57 AM
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I don't think so. But it is common too REGRIND the existing seats, as well as the new valves. New valves and old seats don't commonly fit well. Common valve machines can make them exactly the same angles, and adjust the seat width to the desired spec.

In fact, RJ has developed a grind-angle spec that improves air flow at the valves. See his thread for details. Its a common machining procedure, so most any good engine shop can do this, as long as they have the right angles available in their tools. They should also measure the guide bore diameters to verify the valve fit - too loose will cause untold problems, which is why the bronze guides are often replaced. Also not too expensive, and cheaper that the old-school approach of knurling the guide bores and then reaming them to perfection. [new guides still need to be reamed to correct diameter].

After the seats and valve are reground, THEN you can lap them to perfection.

This MUST be done accurately. Any misfit of the valves and seats will sap the engine's performance, and possibly damage the engine.

It's also common practice to replace the springs - they are not expensive. A really good engine shop will measure the spring heights and tensions, and add or remove spring spacers (they go into the steel spring seats) to match the spring tension across all the valves. Seats live forever, as do spacers (as needed), and the spring retainers and the little valve keepers.



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post #264 of 572 (permalink) Old 10-31-2017, 12:25 PM
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Quote:
Originally Posted by Shakey View Post
What gap?

http://www.alfabb.com/bb/forums/5368265-post2.html

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post #265 of 572 (permalink) Old 10-31-2017, 01:20 PM
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WHAT? You are proposing replacement of the valve seats? Do you know anyone who can that job? It is common practice to replace vales and just re-cut or grind the seats.
Sorry I wasn't more clear. I meant, of course, regrinding the seats. A well done regrind doesn't need lapping, which can fling grinding paste about. A good shop will check the fit of the valve to the seat with vacuum or compressed air.

Last edited by Chas H; 10-31-2017 at 01:25 PM.
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post #266 of 572 (permalink) Old 10-31-2017, 03:05 PM Thread Starter
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Ok, I guess I'll just stick with the old valves.

-Kevin
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post #267 of 572 (permalink) Old 10-31-2017, 03:11 PM
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Shakey, you can stick with the old valves as long as that's what you want to do! New valves, lapped into old seats, are fine. Old valves, lapped into old seats are fine too. If you want to R/R the seats that's a bigger job. Personally, I would never regrind and replace without lapping the valves. Its therapeutic to lap the valves in. Need to make sure you get everything clean afterwards, use soap and water to remove all traces of grinding compound then use brake cleaner, etc.

With respect to guides, a quick n dirty is to see how much vacuum the stem can draw when you retract it in the guide, and how long the vacuum holds.

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post #268 of 572 (permalink) Old 10-31-2017, 06:41 PM
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If you want to do it right lightly cut the seats for a new surface and put in new valves. That would be the minimum. You could resurface the valve faces if you are on a tight budget but then you run the possibility of needing really thin shims. Even if it hurts you will be glad you got new valves down the road. New seats are not necessary for a good rebuild. I've replaced the seats in a couple of heads but my seats had been ground down and the shims were getting pretty thin but the main reason was to have the seat just proud of the edge of the combustion chamber. That aids flow in that the air doesn't have to turn down or up depending on how you look at it to enter and exit the chamber. When you've spent hours porting the head and installing new guides every last little bit helps plus it's kinda fun. On a standard rebuild not necessary for a well performing motor. It's a good, better, best kinda thing. the head doesn't have to be resurfaced everytime it comes off but if it's never been done it's not a bad idea at least have a shop check it for flatness. No matter what you do you will have to adjust the valves! Something that is easy to do is to check the seal of the valves. you can do it with compressed air and mineral spirits but another easy way is to put a strip of the waxed paper that in in a Hersey's Kiss between the seat and valve and points around the valve. let the valve drop down and there should be some resistance when you pull out the strip of waxed paper. If there is no resistance it's not sealing. Again clean everything with scotch brite and brake cleaner.

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post #269 of 572 (permalink) Old 10-31-2017, 07:16 PM
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If the old valves and seats are in good condition, it really is no problem using the old valves in their same position with lapping to assure a good seal.


If you re-assembled in the same order, most of the shims will be in the right range. If you just need a couple of different shims, I'm sure some here would trade you for the right thickness ones!

As you can see, many here are racers and like to go to extremes in preparation and modification.......

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post #270 of 572 (permalink) Old 10-31-2017, 07:57 PM Thread Starter
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Quote:
Originally Posted by spiderserie4 View Post
Thanks Spiderserie4! That's exactly what I was looking for. I hadn't found it in my overhaul manual, nor my workshop manual. I'm not saying it's not in there; I've probably looked past it several times.

-Kevin
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