Big End Bearing Modification - Risk?

[1nsane!]

Hi guys,

Now I know we have quite a few knowledgeable car experts on this forum, so I thought I will post this here.

The engine in discussion: 1600 Ford RoCam

I recently had a mod done to the nose of my crank to allow for a thicker (read stronger) input shaft on my gearbox. When I removed the crank there were marks on 2 of the big end bearings and the guy at the engineering shop told me that it had to be cut to .010" oversize.

So I went out and bought the oversized bearings, fitted the main bearings... All fine, but when I tried to fit the big end bearings, I saw that the bearing has a little notch to position it in the cap and in the conrod, but neither the conrod or the cap has the notches. I phoned up Alert engine spares and Ford SA, neither of them stock this type of bearing in 0.010" oversize.

Ford suggested that I buy a new crank and fit standard bearings... Which is a costly exercise, because I will have to send it back to the engineering shop to machine the nose of the crank for the input shaft.

Now, my question is, I currently have .010" oversized bearings WITH the notches. How big is the risk if I carefully grind away the notches on the bearings outer surface and fit them in the engine?

I have mailed the bearing supplier and asked if they have an alternative for me.

 

[ponder]

You got pictures of all this?

 

[brianj74]

Yes pictures. Thought a notch was an indent and you can only grind away protrusions ?

 

[1nsane!]

I don't have any pics on me, will take some tomorrow night. But, I can easily illustrate what I want to do using pics I got off the net:


The blocks in red are the location lugs with the notches... The big end caps and the conrods are smooth on the inside and does not cater for a location lug/notch.

 

[ponder]

You're not talking about the oil lube holes that line up with the holes in the conrod/cap assembly?

 

[MickZA]

You're not talking about the oil lube holes that line up with the holes in the conrod/cap assembly?

Same thought crossed my mind but it's been years since I last did big ends.

 

[1nsane!]

You're not talking about the oil lube holes that line up with the holes in the conrod/cap assembly?

No, its not the oil lube holes, I got the following reply from the bearing manufacturer:

Our data reflects the Rocam engine here is identical to the one manufactured in Brazil and India with one exception – the conrod bearings in SA were always with lug.
The other countries switched to using bearings without lugs after 2006.

Insofar as the bearings are concerned, please do NOT file the bearings themselves.
Removing the lug from the steel back will leave a weakened area, or perhaps no steel back support at all.

This will in all probability lead to a weakening in the surrounding bearing material, which is totally supported by the steel back.
Bearing material can withstand considerable loads but only whilst it is evenly loaded and the full heat distribution is available.

Some heat is dissipated through the oil and a lot goes out via the contact of the steel back with the bearing housing.
The bearing surface will weaken at the point where the lug would have been, and this will result in a disturbance to the oil film, which is critical at the parting faces of bearings because they are marginally thinner there and the oil ‘pocket’ is larger – remember that bearings are not round and in fact have a complicated variance in wall thickness

The problem is very simple and I suggest you merely file a notch in the conrod in the appropriate place.
Please remember the lug is a LOCATING lug – it has nothing to do with anything other than centering the bearing on the conrod so it is quite safe to take a small square file and make a notch on the conrod.

So I guess that I have a motor from Brazil...

 

[brianj74]

Would not advise notching the conrod big ends across the bearing face. Will create a stress riser.
Can you not split the rod end and drill a hole to accommodate the bearing lug?

 

[1nsane!]

Yup, I am going to file a notch into the conrod and the shell, will do it over the weekend. Will take a few pics.

 

[ponder]

Would not advise notching the conrod big ends across the bearing face. Will create a stress riser.

Thinking the same thing.

 

[brianj74]

Checked with the experts. Notch away, not big stresses on the big end.

 

[Koketso208]

mains oversized bearing

Hello all,

I imagine quite a few in here are experts. I need some assistance and hope you guys can help. I am looking for oversized engine bearing around the Gauteng area. My crank had some damage and the guy the engineering shop proposed machining it and me getting .010" bearings which was supposed to be an easier and more cost effective exercise than buying a crank. I have searched everywhere in the pretoria west area. Nothing. Does anyone know where I can get these for a Audi A3 8P 1.8Tfsi?

Thanx in advance,

 

[Junior1201]

Hello Everyone

My 2016 mazda 2 had a rod knock, my mechanic took the crankshaft to engineering and all and now he says we need 20"big ends and mains but he is struggling to find them, Mazda only has standard one's. Anyone know where I can find the oversized big ends and mains for a Mazda?