Just speccing some engine bearings for my new motor and need confirmation of something.. I'm choosing between these-


Conrod Bearing Set 6B1490
Oversize STD, .25, .50, .75, 1.00
Brand ACL Duraglide
Manufacturer ACL
Conrod Bearing © 1490
Half Type Identical Halves
Manufacturer ACL
Min Std Shaft Size 1.7707in / 44.975mm
Max Std Shaft Size 1.7713in / 44.991mm
Min Std Tunnel Size 1.8898in / 48mm
Max Std Tunnel Size 1.8904in / 48.016mm
Max Wall At Crown 0.0588in / 1.493mm
Max Overall Length 0.7087in / 18mm
Min Vertical Oil Clearance 0.0009in / 0.023mm
Max Vertical Oil Clearance 0.0032in / 0.081mm
Material F780


and these-


Conrod Bearing Set 6B1490H
Oversize Std, .025, .25, .50
Brand ACL Race Series
Manufacturer ACL
Conrod Bearing © 1490H
Half Type Identical halves
Manufacturer ACL
Min Std Shaft Size 1.7707in / 44.975mm
Max Std Shaft Size 1.7713in / 44.991mm
Min Std Tunnel Size 1.8898in / 48mm
Max Std Tunnel Size 1.8904in / 48.016mm
Max Wall At Crown 0.0587in / 1.49mm
Max Overall Length 0.7087in / 18mm
Min Vertical Oil Clearance 0.0011in / 0.029mm
Max Vertical Oil Clearance 0.003in / 0.077mm
Material F781


There for a steel crank with 45mm big ends, hence they are BMW bearings, not Peugeot. The bit I need confirmation of is the 'Max Wall at Crown', is that the bearing thickness? And also the Min and Max 'Vertical oil clearance' I take it this is the clearance between the bearing inner face and the crank journal? And you'd measure that with Plastiguage?

The bearings that came out of it are the top 1490's, but I'm tempted to use the race one's, purely because there called race bearings and will cost me more.

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Oulton Park in a BTCC 306 vid 1
Oulton Park in a BTCC 306 vid 2
Lap of the 'ring

Cheers for that! All the engines I have put together in the past have been standard engines, and I have relied on machinists doing their job right! This time I'm putting it together myself, at least that way if it does blow up I won't have paid someone £1500 to put it together for me!

So yeah, I know it's a long arduos task measuring and re-measuring everything but I'm not taking any chances!

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Oulton Park in a BTCC 306 vid 1
Oulton Park in a BTCC 306 vid 2
Lap of the 'ring

I've got the T-Bar inside mikes, was just gonna measure that with a digital vernier to get the inside measurements, and was gonna measure the outside measurements with the digital vernier also! I've got a 0-25mm mike also. Reckon a 25-50mm mike is required, a vernier does the same job doesn't it?!

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Oulton Park in a BTCC 306 vid 1
Oulton Park in a BTCC 306 vid 2
Lap of the 'ring

Boooo, more money! Ah well, 'spose it's not much in the scheme of things! Whats the point of a vernier measuring to thousandths if there not that accurate?!

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Oulton Park in a BTCC 306 vid 1
Oulton Park in a BTCC 306 vid 2
Lap of the 'ring

Vernier calipers are fairly accurate, it's all down to the person using them. Mic's can also be less accurate than people think. There can be .002" + difference between 2 people's measurements depending on how 'heavy' there feel is. Also once you start using mic's over 0-25/0-1' mic's can be out of calibration and can't be easily checked without an accurate calibrated test bar.
And then there's temperature to contend with........

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www.bridgecraftmotorsport.co.uk

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And there lies the problem! So far I've spent ~£15000 on 3 engines that have been built and/or otherwise f**ked up by "professionals". So this time, if anyone's going to f**k it up, it's me. I have built plenty of standard engines before, but never checked tolerances to such accuracy, assuming the engineers work is correct, and as far as I am aware none of them have gone bang yet! Obviously I'm not going to be so naive as to chuck a race engine together and expect it to work but the only work that will be not be done by myself is stuff I cannot do, such as a crank regrind, grinding the lifter shims etc but I will be checking that work myself.

I would be interested to have a chat with you Midlife, to see what you suggest! I do believe that been the foreman at R-R qualifies you to give me advice

I would love to know if Longmans used to work out clearances with regard to temp etc, must have been quite a task as there 'workshop' was hardly a temperature controlled environment!

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Oulton Park in a BTCC 306 vid 1
Oulton Park in a BTCC 306 vid 2
Lap of the 'ring

I would'nt get too OTT on an engine, if you store and clean your micrometers correctly they stay accurate pretty much indefinitely (Never store them with the anvil closed, and dont ever drop it, a wipe with some light oil once in a while will do fine for keeping corrosion at bay) I'm not trying to say that at RR they don't know what they are doing, quite the opposite. What I am saying is that on a modified production engine (Its not a hyper exotic F1 grenade) there is no tolerance so critical that a +- of 2 thou is anything to worry about. Talk of temperature variation is rather uneccessary when discussing something of this nature (Maybe not when measuring tolerances for the bearings on a gas turbine engine but lets be realistic here)

As for 'feel' yeah, if you gorrilla grip up the barrel on the mike then the anvil will flex giving you an erroneous reading, thats why they give you a ratchet/clutch adjuster bezel to make this less of an issue , however I'd take a few readings to check they come out the same every time when using the ratchet. The ratchet is a good alternative until you develop a feel for the right amount of pressure. (Usually slightly more than the ratchet gives)

The chances are that most if not all of the things you ask your machinist to do will come back close enough to be right for the job, but unless you check everything you will never find out if it really is right until you turn the key, this is a very expensive way to go engine building.

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R H Davey Welding Supplies. I sell new and used welding equipment in the Hampshire area. I take on welding jobs in the evenings, ally casting repairs are one of my specialities but I can weld pretty much anything. PM me with your requirements.

Some of my services: (See my for sale threads)
Engine mount/chassis repair
Solid Beam Mounts BACK IN PRODUCTION
Harness bars

Those bearings above are also available with an additional thou clearance, why would you want that!? Also, the difference between minimum and Max vertical oil clearance is greater than 2 thou, so assuming you're between those 2 figures you'd be ok?

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Oulton Park in a BTCC 306 vid 1
Oulton Park in a BTCC 306 vid 2
Lap of the 'ring

You're gonna have to explain that to me Rikky! Haven't got a clue what you mean!

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Oulton Park in a BTCC 306 vid 1
Oulton Park in a BTCC 306 vid 2
Lap of the 'ring

Sorry, you are quite right Allen,what I meant to say was +- 1-2 ten-thousandths of an inch, this level of accuracy should be achievable with a decant micrometer. I muddle my terminology sometimes when it comes to imperial measurements,please forgive my previous misleading post.

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R H Davey Welding Supplies. I sell new and used welding equipment in the Hampshire area. I take on welding jobs in the evenings, ally casting repairs are one of my specialities but I can weld pretty much anything. PM me with your requirements.

Some of my services: (See my for sale threads)
Engine mount/chassis repair
Solid Beam Mounts BACK IN PRODUCTION
Harness bars

Ah well, just bought one of these- tape measure

apparently it will not only measure everything for me, but then build my engine and make cups of tea, for the price I expected dinner too but can't have it all...

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Oulton Park in a BTCC 306 vid 1
Oulton Park in a BTCC 306 vid 2
Lap of the 'ring

I didn't want to say anything in case it made me look stupid, but now someone else has- Rikky, WTF are you on about?!

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Oulton Park in a BTCC 306 vid 1
Oulton Park in a BTCC 306 vid 2
Lap of the 'ring

Purely guessing but an engine builder may want an oversize bearing if the brand new crank he is using has been ground to top limit to maintain clearances but remain within regulations
Another reason may be down to the oil system, perhaps a high flow pump may perform better with more clearance
I'm just guessing.....

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