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Before updating with the the cylinder head work I completed so far...I was wondering what others do about excessive pinch on the main bearing caps? The factory manual recommends the following....

2019-05-19.jpg

I'm getting a much larger gapping condition .......0.006" & 0.009". I can see how to correct if the pinch is too low (as noted in the manual)...but how to deal with excess? I should mention that when torqued down to full value the cranshaft actually rotates OK I believe. I mean it doesn't continue spinning on it's own momentum if turned....but seems to turns easily enough. What is the general consensus on this?
 

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I'm getting a much larger gapping condition .......0.006" & 0.009". I can see how to correct if the pinch is too low (as noted in the manual)...but how to deal with excess? I should mention that when torqued down to full value the cranshaft actually rotates OK I believe. I mean it doesn't continue spinning on it's own momentum if turned....but seems to turns easily enough. What is the general consensus on this?
I would plasti-gauge the actual bearing clearance, as (I'm not sure) isn't that the most important dimension?

And thanks for the cleaning instructions, and I knew you would have balanced everything :)
Pete
 

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I would plastigauge the actual bearing clearance, as (I'm not sure) isn't that the most important dimension? ....
You're right and will go with the suggestion. I was so hoping to have the crank back from the balance shop by now....but such was not the case....I'll have to wait till next week. In the meantime I ordered some plastigage from ebay....it came in 3 days.

You know that the world is changing when the only place you can get these specialized products nowadays are online. I checked 4 Auto parts suppliers and only one of them knew what Plastigage even was...the others were clueless....mind you it didn't matter because only the one had them listed in their database...but no stock.

I guess in today's throw away society....not many of us are rebuilding engines these days.
 

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...You know that the world is changing when the only place you can get these specialized products nowadays are online. I checked 4 Auto parts suppliers and only one of them knew what Plastigage even was...the others were clueless....mind you it didn't matter because only the one had them listed in their database...but no stock.

I guess in today's throw away society....not many of us are rebuilding engines these days.

Perhaps it's because I'm in Detroit but I haven't had a problem finding plastigauge locally - even from the big box stores. OTOH, I rarely find anyone that knows what I'm talking about...
 

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Wonder if someone rubbed down the bearing caps on a previous rebuild to overcompensate for a worn crank.? What is the downside of larger gapping as you measured.? I have checked the pinch on all the engines I have rebuilt and remember rubbing down some bearing caps and using plastigauge. Curious to see your plastigauge readings.
 

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I had exactly the same issue when rebuilding my Duetto's 1600 (thirteen years ago already--I'm getting old). You can see the thread here.

To cut to the chase, here's what Papajam wrote at the time:

This feeler gauge method is measuring bearing 'crush', an indirect way of measuring bearing clearance. Plain shell bearings, when fitted to the saddle and the cap, do not sit flush with the saddle/cap mating surfaces; they stick up a little bit. When the cap is tightened, the shells are pressed into the saddle and cap, or crushed, as an aid, along with the notches in the bearings, to prevent the bearing from spinning and to obtain proper bearing clearance. Too much crush clearance, as what Alex has, means insufficient bearing clearance. Not enough crush clearance results in too much bearing clearance.

Then came Pastigauge.

One could always use inside and outside mikes and calculate the clearance as machine shops do.
Being Jim, he of course came to my house to help me. Just the nicest guy you could hope to meet. Using an inside and outside micrometer he calculated that the journals were just a touch smaller than spec, but not so much that it would be a problem. I believe Jim also used Plastigauge to confirm his measurements. Both methods were in agreement. He was right (of course) and the engine rebuild turned out great. I get the oil analyzed ever few years and it's always had low metals.

Hope this helps.

Alex


Before updating with the the cylinder head work I completed so far...I was wondering what others do about excessive pinch on the main bearing caps? The factory manual recommends the following....

View attachment 1567190

I'm getting a much larger gapping condition .......0.006" & 0.009". I can see how to correct if the pinch is too low (as noted in the manual)...but how to deal with excess? I should mention that when torqued down to full value the cranshaft actually rotates OK I believe. I mean it doesn't continue spinning on it's own momentum if turned....but seems to turns easily enough. What is the general consensus on this?
 

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Discussion Starter #1,530
I resolved my problem of excess pinch on the main caps after studying the informative bearing guide by Mahle..

https://www.mahle-aftermarket.com/media/local-media-north-america/product-files/ceb-2-1114-engine-bearing-failures-brochure.pdf

I came to the conclusion (obvious now) that the bearing shells come slightly over length from the manufacturer and the ends need to be ground down (in my case about .004" each). So I carefully wet ground them down 0.001" at a time using a fine flat grinding stone, then reassembled and checked again....repeating these steps until achieving the required .003"-.0039" of crush. Once satisfied with that, I verified using Clevite plastigage that the clearance was within 0.0006"-0.0022" factory spec.

20190609_152746.jpg

My final gaps are all at 0.0015" which is above the mid point range....but I think I prefer to be a little looser than too tight. Next I will need to repeat the same process for the connecting rod ends.
 

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Checking out the bottom end details and I have a feeling that the lower timing chain might be stretched. However I do not see anything in the factory manual that tells us what the length should be. What should be the method of checking this exactly? I know reproduction chains are available...but how good are they really?
 

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Checking out the bottom end details and I have a feeling that the lower timing chain might be stretched. However I do not see anything in the factory manual that tells us what the length should be. What should be the method of checking this exactly? I know reproduction chains are available...but how good are they really?
Go with IWIS chains, then you're on the safe side,

KR

Thomas
 

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There’s a mod that allows for a silent bloc/tensioner to be mounted in the casting to the bottom left (7-8 o’clock). I can’t remember the thread. From memory it’s a standard piece available for many, many engines.

Other vendors available, etc...

https://www.alfaholics.com/parts/105-series/engine/timing-chain-tensioner-lower-chain/
Can't remember if I've seen it here but there's a mod using mini parts (as far as I remember) to recreate the Alfaholics part.
 

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I wonder how long a new chain lasts? I think not long, as its a bad design as the shafts are too close together meaning the chain spends most of its time going from straight to turning ... promoting wear. Adding a tensioner probably makes the chain stretch quicker as more link turning ...

Luckily this flaw does not produce a timing chain rattle like for example the original Mini (replace timing chain and by weeks end they rattle again).

I know the Chysler v8 of the 70s uses a different chain design which MIGHT be superior in this sort on installation ... but one heck of a reengineering job
Pete
 

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I have put new repro chains on 3 Alfa engines I rebuilt.
Do you recall the brand name of those? Was there a noticeable difference in droop between the old and new chains though?

That thing is overkill for a street engine. A new chain is the way to go.
I was going to agree totally with you on this. But note that the Montreal engines utilize such a tensioner on the lower chain as well....there must be some benefit on the use.

I wonder how long a new chain lasts?
We might not ever find out...at least not until those engines get rebuilt.

I'm not planning on doing any performance mods whatsoever to this engine. My aim is to keep it all original and I hope that emissions will be close to what the engine achieved at the time as well. Ideally I was hoping that there was a way of checking the length....or amount of droop on the original chain.
 

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I was going to agree totally with you on this. But note that the Montreal engines utilize such a tensioner on the lower chain as well....there must be some benefit on the use.
It's a different engine. If you want to know the benefits of that gizmo, talk to an engine builder who specializes in race engines. IMHO, it's overkill for a street engine. Yours is going to be stock, so it's even less necessary.
 
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