Con Rods

[4wDaz]

Would an engine come from the factory with all the same size conrods ? for example 4 no 2s ? or is it acceptable to mix them if the weights are the same ?

[McCabe-Thiele (Ted)]

Mine were the same weight code but had different code numbers  on the two that were still legible. Likewise two different codes on the crank webs.
Pretty certain they are original conrods.

[4wDaz]

Ive read your posts with interest as Im just measuring up to order new bearings, unfortunately no markings are legible on the crank only on the rods, 3 number 2 and a 3. I do have a spare number 2 from another engine so I was thinking I could make a matching set if required

[McCabe-Thiele (Ted)]

Ive read your posts with interest as Im just measuring up to order new bearings, unfortunately no markings are legible on the crank only on the rods, 3 number 2 and a 3. I do have a spare number 2 from another engine so I was thinking I could make a matching set if required

I didn't find the crank web marks either the first time or the second time when I looked.
It needed me to clean the crank webs with some fresh petrol then concentrated  looking in right place I found two of [ Guests cannot view attachments ] them.
Not easy to photograph with a phone - even now it takes me a while to find the marks again but they are there on my crank.
I have recored my crank mains, conrod details on a spreadsheet for future reference.

.

[Bryanj]

More the point you need matching weights not sizes

[royhall]

You cant always find the crank markings, on my 350F (or it could have been the 750K4 memories eh) they simply had disappeared. I tried the petrol trick and used a very bright LED magnifying lamp but never did find them. If that's the case you will need to measure them very accurately with a calibrated micrometre (this is to tenths of thou's), if you cant do it go to a machine shop and get them to measure them for you. It's very important that you get the correct size shells.

[4wDaz]

More the point you need matching weights not sizes

Ok Thanks, the current Con rods are all the same weight C, plus the spare Con rod I have is also a C. Would it have left the factory with different size rods but the same weights ?

[4wDaz]

You cant always find the crank markings, on my 350F (or it could have been the 750K4 memories eh) they simply had disappeared. I tried the petrol trick and used a very bright LED magnifying lamp but never did find them. If that's the case you will need to measure them very accurately with a calibrated micrometre (this is to tenths of thou's), if you cant do it go to a machine shop and get them to measure them for you. It's very important that you get the correct size shells.

I’ve tried but can’t read anything. I have treated myself to a new Mitutoyo digital micrometer and successfully measured the crankshaft journals but I have nothing  to measure the crankcase with yet 

[McCabe-Thiele (Ted)]

You cant always find the crank markings, on my 350F (or it could have been the 750K4 memories eh) they simply had disappeared. I tried the petrol trick and used a very bright LED magnifying lamp but never did find them. If that's the case you will need to measure them very accurately with a calibrated micrometre (this is to tenths of thou's), if you cant do it go to a machine shop and get them to measure them for you. It's very important that you get the correct size shells.

I’ve tried but can’t read anything. I have treated myself to a new Mitutoyo digital micrometer and successfully measured the crankshaft journals but I have nothing  to measure the crankcase with yet

Did you find any markings on the shell edges ?
I had to do a bit of educated guesswork from the ones that were colour coded then try them in an unmarked conrod using Plastigauge to check the clearance.
My understanding is that you do not have to measure the crankcase as they are stamped with the codes.

[Bryanj]

Yes the rods could be different sizes but same weight from new and the cases will be stamped and wont changesize uless the shells sieze to crank and spin which would destroy the cases anyway

[4wDaz]

Did you find any markings on the shell edges ?
I had to do a bit of educated guesswork from the ones that were colour coded then try them in an unmarked conrod using Plastigauge to check the clearance.
My understanding is that you do not have to measure the crankcase as they are stamped with the codes.

No unfortunately, the crank had been removed from the engine by a previous owner years ago and the shells had been lost. Luckily the con rods were still attached but pistons had gone

[4wDaz]

So is it possible to get the bearing size without measuring the crankcase ? The cases are marked BBBAA
 
The main crank journals measurements are
No 1 – 31.986
No 2 -  31.986
No 3 – 31.987
No 4 – 31.988
N0 5 – 31.985

[Bryanj]

In the manual and the parts book is a cross reference table and in that you can convert the pin sizes to codes then use the table to get colour codes

[McCabe-Thiele (Ted)]

If you look at the tables in the parts manual you will see that they used different markers in the tables. Letter codes on one axis for mains shells, the same axis in big ends uses number codes.
I too found it confusing - over time it makes sense - also the table layout themselves are obvious I guess to an engineer it was difficult for me to see the symmetry in the columns if you get my meaning.

[4wDaz]

Thanks i'll have a look when i get home from work and see if i can work it out. Im no engineer and moneys tight so I cant afford to order the wrong bearings, I'm sure i'll get the hang of it in the end