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> Crankshaft Big End Journals, Advice Please!
zanetti
post 11th March 2018 16:49
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I've just stripped my CF1 16v 2.0 twin spark engine, was running well but I had removed the sump and although being covered, the bottom end got quite dirty so a strip and clean was necessary.

The question I have is 1,2 and 3 big end crank journals are all mic'ed at 49.57mm I unfortunately don't have a vernier mic so thats as close as I can get.

However number 4 is 49.44mm all were fitted with 30 thou bearings. All bearing are in pretty good nick nothing really wrong with them and the mains are like new!

None of the journals are damaged, no scoring or marks and no oil pressure issues.

What I need to know is should I just replace with new 30 thou bearings and see how it goes, mostly because I'm on a really tight budget, or put a different size bearing on number 4 to keep oil clearance within limits or crank work?

Anyone with any experience here?

PS. The journal to bearing measurements don't seem to add up if I go by the workshop manual, the rods are stock.

This post has been edited by zanetti: 11th March 2018 17:19
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Ganz
post 11th March 2018 22:38
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If you got no oil pressure probs I wouldn't worry. When I had my cylinder head cleaned and skimmed with new valve seals it was discovered that I had three bent valves eek.gif Now here's the thing. Before I took the 145 off the road for the rebuild there was no indication of anything wrong. So how is it possible that I had three bent valve stems when the engine was running great. It used oil for sure but that's Alfas no? When I say bent valve stems I'm talking about microns that you are talking about on your crank journal. The head recon chap showed me the valves and for sure you can see when he recut the valves these valves were catching on one side only.

I mentioned this to my garage next door neighbour and he said he was not surprised in the slightest! What..!! I thought. My garage next neighbour worked in the aviation industry for Lockheed in the US and said this. Car engines can have quite large tolerances and they will still work fine. The tolerances of mass produced vehicles can have differences as wide as yours and still work fine. Unlike the aviation industry where a difference like yours would not be allowed to happen because of the extreme stresses uncurred by aircraft.

I wouldn't worry about it unless you are going to rev it to 7k all the time. it's not something that will consume oil unlike bent valves. I have noticed since I had my cylinder head recon it doesn't consume oil at all.

This post has been edited by Ganz: 11th March 2018 22:38


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dante giacosa
post 11th March 2018 23:40
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that is genuinely a fascinating anecdote, Ganz-

Thanks for sharing that..

I suppose they are; all 'just' cars..!

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zanetti
post 12th March 2018 05:17
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QUOTE(Ganz @ 12th March 2018 00:38) *
If you got no oil pressure probs I wouldn't worry. When I had my cylinder head cleaned and skimmed with new valve seals it was discovered that I had three bent valves eek.gif Now here's the thing. Before I took the 145 off the road for the rebuild there was no indication of anything wrong. So how is it possible that I had three bent valve stems when the engine was running great. It used oil for sure but that's Alfas no? When I say bent valve stems I'm talking about microns that you are talking about on your crank journal. The head recon chap showed me the valves and for sure you can see when he recut the valves these valves were catching on one side only.

I mentioned this to my garage next door neighbour and he said he was not surprised in the slightest! What..!! I thought. My garage next neighbour worked in the aviation industry for Lockheed in the US and said this. Car engines can have quite large tolerances and they will still work fine. The tolerances of mass produced vehicles can have differences as wide as yours and still work fine. Unlike the aviation industry where a difference like yours would not be allowed to happen because of the extreme stresses uncurred by aircraft.

I wouldn't worry about it unless you are going to rev it to 7k all the time. it's not something that will consume oil unlike bent valves. I have noticed since I had my cylinder head recon it doesn't consume oil at all.



Thanks Ganz very interesting and you make a very valid argument!

Many people will disagree but back in the day it was quite common to have different size bearings on the same crank, new from the factory where the car was built and that worked perfectly.

My experience also with these engines also is that they drive seemingly grerat even when there is something "wrong" with them! People have looked at me like I'm crazy for not boring my block after 200K kms but the truth is all it needed was a deglaze and new rings!
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Antonio
post 13th March 2018 22:40
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If you canīt get decent measuring tools, look at buying plastigauge wich will help you to know tolerances between each journal/shell, so you can choose the right shell for you..you can also look at paint marks at the crank and the sticker fitted at the phonic wheel to look at factory journals classification.


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zanetti
post 14th March 2018 05:30
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So I went and recalibrated my mics (just to be sure) and did a complete set of measurements. With the 030 big end bearings I'll have 0.02mm of oil clearance which is quite tight but within spec according to the workshop manual. So all good!
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langers
post 14th March 2018 17:16
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Pay particular attention to number 3. That is the one that normally spins in the event of an engine failure due to it being closer to the sump housing and exhaust temperatures.


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Antonio
post 14th March 2018 21:31
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QUOTE(zanetti @ 14th March 2018 08:30) *
So I went and recalibrated my mics (just to be sure) and did a complete set of measurements. With the 030 big end bearings I'll have 0.02mm of oil clearance which is quite tight but within spec according to the workshop manual. So all good!

Sounds quite right, they always round somewhere between 0.25mm, it will help on reducing oil flow loss wich TS 16v suffers a bit, so all great!
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dante giacosa
post 15th March 2018 08:13
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Hey Langers-

can you expand on that?

My local specialist told me to take off the exhaust-sump-heatsink-guard thing, as it would catch the ground.

(it didn't) but they took it off anyway and said not to worry as they had 'never seen any evidence' of shells' deterioration due to heat...

I really had no idea what they meant...
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langers
post 15th March 2018 20:02
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I know of at least 4 engines suffering from exactly the same thing, number 3 shell spinning... 2 of my own cars and 1 other that we ended up putting a 20VT in.
Your local specialist is quite right in what they said, its a pointless item and will pull the sump off if hit.


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zanetti
post 16th March 2018 05:39
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QUOTE(Antonio @ 14th March 2018 23:31) *
Sounds quite right, they always round somewhere between 0.25mm, it will help on reducing oil flow loss wich TS 16v suffers a bit, so all great!


Great!

QUOTE(langers @ 14th March 2018 19:16) *
Pay particular attention to number 3. That is the one that normally spins in the event of an engine failure due to it being closer to the sump housing and exhaust temperatures.


No 3 looks good, just polished them with 1000 grit paper and marine metal polish paste up to a mirror finish, all still within spec on the mics coolio.gif

This post has been edited by zanetti: 16th March 2018 05:39
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Ganz
post 17th March 2018 20:39
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QUOTE(zanetti @ 12th March 2018 05:17) *
Thanks Ganz very interesting and you make a very valid argument!

Many people will disagree but back in the day it was quite common to have different size bearings on the same crank, new from the factory where the car was built and that worked perfectly.

My experience also with these engines also is that they drive seemingly grerat even when there is something "wrong" with them! People have looked at me like I'm crazy for not boring my block after 200K kms but the truth is all it needed was a deglaze and new rings!


Agree. I'm on 145000 miles and engine feels great. When I had the head off I looked at the bores and they were in good fettle. No lip or score marks. Always top the oil and keep an eye on temps.


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