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Pre-unit crankcases compability #82516
08/24/05 5:12 pm
08/24/05 5:12 pm
Joined: Aug 2005
Posts: 31
Sweden
D
Dan B Offline OP
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Dan B  Offline OP
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Joined: Aug 2005
Posts: 31
Sweden
Rebuilding a 1951 6T 650 cc pre-unit engine.
One lip for the two screws in the crankcase throut is broken. I've got a good 1954 crankcase.

I'd like to use the 1954 crankcase. Am I right presuming that the crankcases are equal? Or is there something I must look out for?

Thunderbird Dan.

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Re: Pre-unit crankcases compability #82517
08/24/05 5:24 pm
08/24/05 5:24 pm
Joined: Apr 2005
Posts: 441
Huntington Beach, CA
scootermcrad Offline
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scootermcrad  Offline
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Joined: Apr 2005
Posts: 441
Huntington Beach, CA
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.


ScooterMcRad
Re: Pre-unit crankcases compability #82518
08/24/05 5:27 pm
08/24/05 5:27 pm
Joined: Apr 2005
Posts: 441
Huntington Beach, CA
scootermcrad Offline
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scootermcrad  Offline
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Posts: 441
Huntington Beach, CA
HAAA! That was you that started that thread. Oops! Sorry for the wasted babbling...


ScooterMcRad
Re: Pre-unit crankcases compability #82519
08/24/05 7:42 pm
08/24/05 7:42 pm
Joined: Aug 2005
Posts: 31
Sweden
D
Dan B Offline OP
BritBike Forum
Dan B  Offline OP
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Joined: Aug 2005
Posts: 31
Sweden
Thanks!

laugh

Re: Pre-unit crankcases compability #82520
08/25/05 5:10 pm
08/25/05 5:10 pm
Joined: Aug 2005
Posts: 31
Sweden
D
Dan B Offline OP
BritBike Forum
Dan B  Offline OP
BritBike Forum
D
Joined: Aug 2005
Posts: 31
Sweden
Hmm, there are different spare part numbers for the crankcases listed in Roy Bacons "Triumph Twin restoration".

1951 crankcase = E2892 and E2893
1954 crankcase = E3314 and E3281

Big main bearing was used from 1954.

This is the only difference I've found so fare between the cases.


Left -51 case. Right -54 case with a shell.

Ok, But what does this means? Can I use -51 crankshaft with -54 main bearings? Or do I put a shell in the -54 crankhouse and use a -51 (small) bearing? Or should I look for a -54 crankshaft?

confused

/Dan Thunderbird

Re: Pre-unit crankcases compability #82521
08/25/05 8:04 pm
08/25/05 8:04 pm
Joined: Aug 2001
Posts: 96
Northern Virginia / USA
B
Brent Pinkstaff Offline
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Brent Pinkstaff  Offline
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Joined: Aug 2001
Posts: 96
Northern Virginia / USA
Dan,

I am confused here. Are you trying to use the left half of a 1951 case and the right half of a 1954 case, or are you just trying to use a set of 1954 cases?

Here is a breakdown of pre-unit 650 cases:

Left side:
E2892 1950-1962 all (E1591 bearing)

Right side:
E2893: 1950-53 6T (dynamo) (E2877 bearing)
E3282: 1954-59 T110/TR6/T120 (dynamo) (E1591 bearing)
E3314: 1954-59 6T, 1960-62 all (alternator) (E1591 bearing)

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.

Hope this helps,


Brent Pinkstaff - Falls Church, VA
'38 5T
'46 T100
'48 5T
'50 TR5
'50 6T
'58 TR6/A
'59 T120
Re: Pre-unit crankcases compability #82522
08/26/05 6:29 am
08/26/05 6:29 am
Joined: May 2003
Posts: 48
coventry
M
mike750triton Offline
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mike750triton  Offline
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M
Joined: May 2003
Posts: 48
coventry
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
08/26/05 7:07 am
08/26/05 7:07 am
Joined: Jun 2005
Posts: 16
Finland
J
JanneK Offline
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JanneK  Offline
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Joined: Jun 2005
Posts: 16
Finland
A little bit related - about the cracnshafts.

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...

-Janne

Re: Pre-unit crankcases compability #82524
08/26/05 11:38 am
08/26/05 11:38 am
Joined: Aug 2001
Posts: 96
Northern Virginia / USA
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Brent Pinkstaff Offline
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Brent Pinkstaff  Offline
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Joined: Aug 2001
Posts: 96
Northern Virginia / USA
JanneK,

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.


Brent Pinkstaff - Falls Church, VA
'38 5T
'46 T100
'48 5T
'50 TR5
'50 6T
'58 TR6/A
'59 T120
Re: Pre-unit crankcases compability #82525
08/31/05 6:01 am
08/31/05 6:01 am
Joined: Jun 2005
Posts: 16
Finland
J
JanneK Offline
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JanneK  Offline
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J
Joined: Jun 2005
Posts: 16
Finland
Brent Pinkstaff,

Thanks for the detailled info - have to write it all down and try to figure out what I actually have there inside.

Yes - those cases are re-stamped. It is clearly visible that somebody have grinded and smoothed the numbering area - it's looking so different of the other surrounding surfaces on the blocks.

-JanneK

Re: Pre-unit crankcases compability #82526
11/13/05 4:27 am
11/13/05 4:27 am
Joined: Oct 2005
Posts: 157
capecod ma.
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pre-unit Offline
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Joined: Oct 2005
Posts: 157
capecod ma.
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

http://www.imagestation.com/album/pictures.html?id=2118754277&idx=15

by some insane odds, it broke while splitting the cases! had it ran for 1 second longer there would be one less set of 50 cases in this world! crazy!


who ever doesn't take a chance never has a chance.

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