Dan B, I'm not sure about the component compatibility, but I think I read somewhere once that you may have to have the top of the cases, around the throat/mouth where the jugs drop in, decked so they match and create a good seal. Don't know if that's true, but I'm sure someone on here would know. Someone just started a thread on rather or not you need the inner screws in the mouth there. You may want to check that out too.
Basically, if you are going to use anything but the E2893 right side case then you have to use a 1954 and later (big bearing crank). The biggest trick in mating two non matched Triumph cases is your cam bushings. You HAVE to press new ones and ream them with the special tool with the cases assembled. You are better off having the two center screws in when you do this as well. The top mating surface for the cylinder block can be a concern, but you can true this with a good bastard file by hand.
The big bearing crank is actually a nice upgrade for the 650s. Especially if you are going to beat on it at all.
pre 1954 small bearing cases have other differences to the later ones. you can fit 650 barrels to 500 cases on big bearing cases but not prior to that. the stud spacing for the barrels on earlier 500 cases is 2 inch, 650 are 2 1/8 inches. later cases are all the same at 2 1/8"
my 2 bobs worth
Re: Pre-unit crankcases compability#82523 08/26/057:07 am08/26/057:07 am
How is this change from from older "three-piece" crackshaft to newer "one-piece" crankshaft related - or is it? What I mean is that did this crankshaft change happen at the same time (i.e. for year '54) as the timing side bearing change.
And how about then that connecting rod big end bearing change from "small" (white-metal coated) to "big" (separate bearing shells)?
About cases - is there inside cases somewhere those year labels (last two digits of year surrounded by "beams") like in some other alloy parts (e.g. my rocker boxes and cylinder head have those)?
I just try to figure out what I have since somebody have "modified" the serial number stampings on my cases - it says "T120 45189" which is totally inconsistent ('54 T120 - hah!)? They are a matching pair of alternator type big bearing cases...
Re: Pre-unit crankcases compability#82524 08/26/0511:38 am08/26/0511:38 am
The change to the big bearing crank was non related to the change to the one piece.
Triumph used 2 one-piece 650 crankshafts in the pre-unit engines (and one for the pre-unit 500 in 1959, but we are talking about 650s). The first was used from 1959-early 1962. The second was used for the remainder of the 1962 model year.
The change to the separate shell bearings for the 650 connecting rod big end was done in 1956.
As far as part numbers on cases: The left side case has a part number inside of it, the right side case has a part number on the outside, in the timing area. I am not 100 percent sure that the part number on the cases always cooresponds directly with the part number in the book (I know that it sometimes does). A lot of times, the part number in the book is the number assigned to a finished item, not the actual casting number.
Sounds like your cases are restamped! There should be a date code on the right side case in the timing area, which will give you an idea of what year the engine originally was.
ok. since this thread is already alive i'd like to ask some more on the topic. i have the small bearing (50) cases and want to change to a later crank. i understand i'd need a bearing conversin for the later large bearing w/connecting rods that use shells as well BUT what about a 1 pc? is the one peice simular to the 54 and later crank? what mods would i need to do to fit a later one pc. crank into a small bearing case? could i get away with this with having the crank snout turned down? is there any other mods needed to fit a 1pc crank? one more thought? by using the 1pc crank would i have to run an stator? from what i've gathered the snout of a crank from a generator motor is threaded and the later smooth. HELLP! i'd really like to start obtaining some pieces to this ol' girl and don't want to do it twice. if the 1pc is fairly reasonable to do i'd like to do it now while i'm at this stage. btw. here's my 2 pc one