Advice needed on bearing clearances please.

[fingersnfumbs]

Hi Guys,
Im a long time lurker and proud owner of a mk2 Mexico.
I need a bit of help from the collective.

Im currently building up my Pinto and have had the crank re ground.

I have carefully measured the bearing clearances with Plastigauge and have the following which seem a bit loose to me.

Mains:
No1 0.050mm
No2 0.050mm
No3 0.063mm
No4 0.063mm
No5 0.063mm

Big Ends:
No1 0.076mm
No2 0.076mm
No3 0.076mm
No4 0.063mm

I know a lot of people dont like or trust Plastigauge but I used a reputable machine shop and they said I dont need to check clearences anyway as long a I buy good quality shells of correct size. (Mains +0.25) Ends (+0.50)
I have bought the shells as recommended from Burtons Mahle VC.
Any help or advice greatly appreciated, its my first engine build and I really dont want to put it all back together only to have either no oil pressure or a tight engine that knock the bearings out in no time.

Many thanks in anticipation.

[Graham]

clearances are on the loose side, but theres no issue with that

[fingersnfumbs]

Phew, thats a relief.
Cant thank you enough Graham.

Do you think it will effect oil pressure?
Oil pump will be brand new but standard.

[Graham]

no, you would need to double or triple those clearances to any any effect on oil pressure.

the old school rule of thumb is you need 1 thou clearance for every inch journal diameter, you have a little over that, but on a performance engine you would grind it to be bottom or slightly below bottom clearance anyway

[fingersnfumbs]

A great relief,
I was getting confused with thousands of an inch and mm.

Sort of tied myself in knots and it didnt help that bearings are sold as + something, Engine shop work in thou and rod manufacturers etc seem to do both.

Even more confusing Plastigauge range on the metric side is 0.025 - 0.175mm.

I think I have gripped it now.

[HonkyWhiteTrash]

Phew, thats a relief.
Cant thank you enough Graham.

Do you think it will effect oil pressure?
Oil pump will be brand new but standard.

Be careful whose pumps you use. An original Ford used one in good condition is likely to be far better than most repro. There are enough scare stories around to make you avoid new if possible.

[Graham]

Even more confusing Plastigauge range on the metric side is 0.025 - 0.175mm.

thats because its really old and actually sized in half thou increments (0.0005) it cant be an even number in both scales.

i work in an odd mix of both, bore and stroke sizes i do in metric, but bearing and tappet clearances i do in imperial. valve lift i understand in metric but usually convert to imperial as it means something without having to think about it.

[Forest_rallying]

clearances are on the loose side, but theres no issue with that

When I left School I went to work in a Garage, there was an old Boy there and he said there was nowt like a worn engine for performing well. I suppose what he was meant to say that a worn engine has less friction and that results in more power.

[fingersnfumbs]

Yep,
I Think we are similar ages, I learnt both at school and didnt master any of them.
Im a Heating Engineer by trade and boilers are rated these days in KW. Just cant get my head around it. Tell me you have a 55,000 BTU boiler and I know exactly what you mean, I can picture it in my head.
Pressures are even worse, Bar, kPa, Inches of water and PSI thats where Im most at home.

Im going to do the ring gaps next.

[Miniliteman]

Im going to do the ring gaps next.

In mm or inches??

[fingersnfumbs]

Both.

[Graham]

Im going to do the ring gaps next.

dont worry too much about ring gaps as long as they are not too tight all will be fine, old school rule of thumb is 0.003" which in metric means you want about 0.25mm but as i said bigger isnt an issue unless its about a 1/4 inch!

[katana]

i work in an odd mix of both, bore and stroke sizes i do in metric, but bearing and tappet clearances i do in imperial. valve lift i understand in metric but usually convert to imperial as it means something without having to think about it.

Nowt wrong with ordering 3m of 2x4" lumber or 8x4' sheet of 13mm ply or plasterboard LOL!
Everyone understands miles / gallon - who knows how far you'll get with a gallon of fuel at 5L/Km LOL!
I will work in whatever range the measuring device I pick up is marked in - as long as I don't have to convert on 'the fly' i'm fine!

[rallyrob]

Yea I'm the same, I do some things in imperial and some things in metric.

[wildo105e]

My kids are 16 and 19 and play football. They have never been taught imperial. But can judge 25 yard free kicks.

I am the same as you lads 1/2 and 0.5


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[onecamohv]

i do everything in mm except for engine building. i do all my engine builds and measuring in thou's. i think its just easier to 'picture' and all the books ive read, all the refernces i have and older guys ive learned from are imperial, so i just stuck with it.
For the bearing clearances - they're a bit on the loose side but ok with the right oil grade. you wouldnt want to be going much more. excessive bearing clearance will put more load on the mid point of the top and bottom shells.

Tighter bearing clearances reduce vibration in an engine, spreads the load more over the complete bearing, but also requires more precise and accurate machining. If you haven't accurately line bored the mains with a tight main bore geometry (less than .002˝), you shouldn’t run tight clearances.

A rule of thumb for the top ring is .0045" of end gap per inch of bore diameter for an n/a engine. Alot of top motorsport ring suppliers recommend opening up the second ring .005" to .008" more than the top ring gap in naturally aspirated engines to prevent gas build up between the top and second rings and cause the top ring to flutter.

Graham is right in saying having ring gaps slightly too big is better than them butting, you really dont want that. but you may aswell get it right while you're in there, excessive gap wont be good either. anything over .025" more than the upper end of the spec will be noticeable on a leak down test usually

[Graham]

Graham is right in saying having ring gaps slightly too big is better than them butting, you really dont want that. but you may aswell get it right while you're in there, excessive gap wont be good either. anything over .025" more than the upper end of the spec will be noticeable on a leak down test usually

i once rebuilt a mk2 cavalier engine for my boss 1600ohc 8v j series engine, he wouldn't pay for a rebore or new pistons, i honed the bores like hell to get them looking half decent, when i checked ring gaps we had about 45 thou! it went together like it, it never smoked or burnt oil. my boss said it went like hell, fastest 1.6 cav or astra he had ever driven by a long way, and back then every other car seemed to be a mk2 cav or astra

[onecamohv]

i once rebuilt a mk2 cavalier engine for my boss 1600ohc 8v j series engine, he wouldn't pay for a rebore or new pistons, i honed the bores like hell to get them looking half decent, when i checked ring gaps we had about 45 thou! it went together like it, it never smoked or burnt oil. my boss said it went like hell, fastest 1.6 cav or astra he had ever driven by a long way, and back then every other car seemed to be a mk2 cav or astra

yep theres always things that go against everything we've been thought!

i had a toyota 4K one time that burned no oil, ran like hell. when i pulled the head to do a bit of a valve job on it, i found a cracked piston and a broken top ring. ran perfect. ive no idea how long it was like that