Forum

[tribonnie]

A question ..... why are crankcase halves numbered as a pair


I always thought this was because they were machines as a pair to ensure the critical areas, crankshaft, camshaft and dowels, etc. were aligned.


But ...... (as a member of a well known Norton forum pointed out)


Crankcase bearings are fitted, and hence machined, from the inside. A lot of single cylinder engine have the cams in one half of the crankcase only. Dowels are fitted into the machined face so again cannot be machined with the halves together.


Also both the Norton and Redditch Enfields quoted one side of the crankcase as a spare part


So ..... seems to me we are down to getting the stud holes aligned and the crankcase “deck” height for the barrels. As the stud holes are not a close fit and the deck height is easily machined to match. Also, I have seem perfectly good running engines with mismatched numbers


Does it really matter if the numbers don’t match ?


Richard

[apparently lucky eddie]

In a word - no. I've had a number of bikes with "mis-matched" cases than were perfectly ok. The only proviso of course is that the cases are identical to the damaged or replaced one. Most recently I had to replace the bottom engine case (horizontal not vertical join = fewer oil leaks)of a 750 Honda F1 after a loose chain jumped the front sprocket and trashed the case. Replaced it with an engine case from the same year and model and had no probs at all.
And the top and bottom type cases make it soooo much easier.

[Alan R]

Hello AL EDDIE !! --------------- Tut, Tut,... naughty young Mr Eddie, slack chain ?? BUT, as expected, HONDA quality (Built-in all those years ago remember) comes up trumps !!.... In the local South Staffs Branch of the VJMC club one of the lads has an F1 that is 25,000 miles into its' SECOND time around the clock and STILL runs A-OK !!!------------"They'll never make big bikes"--eh ??

[Mark M]

I think you've answered your own question! If an engine runs ok with mis matched halves someone has probably assembled it to take account of irregularities in deck height etc. But in a factory they can't be messing about matching loose pairs so a unique identity makes sense. And it's not as simple as it appears, RE twins have both drive main bearings and cam housings that are machined from outside the case. Just a quick thought!
REgards, Mark

[Norm]

From what I have heard the early Indian built Enfields were not line bored and they chewed out main bearings quickly