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Old 12-18-2011, 12:30 PM   #1
marksbonneville OP
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Triumph 750 engine tear down question.

I'm doing a tear down of my '73 750 Bonneville to replace the crankshaft (alternator rotor disaster), my question is do I need to remove the transmission from the block to split the case? I thought with the later blocks the gears could stay in place but I honestly can't remember.
The rest of the engine is in great shape so I only want to take apart what is absolutely necessary.

Thanks.
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Old 12-18-2011, 03:39 PM   #2
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No - but you'll have to remove the clutch and gearbox outer cover.
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Old 12-18-2011, 07:29 PM   #3
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No - but you'll have to remove the clutch and gearbox outer cover.
Thanks Motu
Yes I have the clutch assembly off already, and was aware of removing the outer (shifter kick-start cover), I did not want to remove the transmission if I don't have to.
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Old 12-18-2011, 07:44 PM   #4
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On my '71 T100 I didn't have much problem pulling the guts out of my transmission after I had removed the clutch/drive gear. I don't exactly know how the later T140's went together but I don't imagine that there was much difference. It might be a good time to look at your transmission components. Sorry to hear about the problem with your crank. Did your rotor come apart from the body? I caught mine just before it let go on my old Trophy - bought a new one and never had a problem again.
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Old 12-18-2011, 08:00 PM   #5
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On my '71 T100 I didn't have much problem pulling the guts out of my transmission after I had removed the clutch/drive gear. I don't exactly know how the later T140's went together but I don't imagine that there was much difference. It might be a good time to look at your transmission components. Sorry to hear about the problem with your crank. Did your rotor come apart from the body? I caught mine just before it let go on my old Trophy - bought a new one and never had a problem again.
I really don't want to mess around with indexing the gear box so if I can leave it alone I will, it only has 8500 miles since a major overhaul. The rotor literally exploded into the alternator while I was going down the road at 65mph, sudden stop of the engine is an understatement. The rotor key on the crank sheered preventing any other damage and I clutched quickly.
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Old 12-18-2011, 08:16 PM   #6
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You'll have to pull the inner gearbox cover anyway, and it's a lot easier to rebuild the motor with the gears and shafts out. Indexing these things is easier than you might have been led to believe.
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Old 12-18-2011, 08:22 PM   #7
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You'll have to pull the inner gearbox cover anyway, and it's a lot easier to rebuild the motor with the gears and shafts out. Indexing these things is easier than you might have been led to believe.
I was under the impression the case bolts were under the outer cover? I honestly don't remember the last time I had a Triumph transmission apart.
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Old 12-19-2011, 01:33 AM   #8
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It's a long,long time since I've had one apart too, but I'm sure it's just that one bolt behind the inner cover - some used to cut the cover extension off so the cases could be split without disturbing the outer cover at all.
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Old 12-22-2011, 11:53 AM   #9
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I think it will be easier to get it all apart without the gearbox internals in it, they might all fall out anyway when you try splitting the cases.
Don't forget the hollow dowel where the front engine mounting bolt goes through.
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Old 12-22-2011, 02:57 PM   #10
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I did one last winter, (1973 T140 Bonneville) and took the transmission apart to inspect, replace seals when I split the case for the crank removal. The phasing of the shifter isn't bad, followed the book for a while, but the Clymer only gave procedure for the 4-speed. I just figured it out for the five speed. Pretty sure there is a bolt in behind the "inner" transmission cover, IIRC
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Old 12-22-2011, 07:54 PM   #11
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marksb'ville's memory is right, and mine was wrong. One summer in the late '70s, it seemed like all I did was rebuild unit 650/750 motors-or more accurately, replace crank bearings. Not only did we leave the gearbox internals in place, we also lefft the cam gears on.

If it hasn't been mentioned already, pull and clean the sludge trap. and repalce the rod bolts.

Wherever you are Dad, thank you.
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Old 12-23-2011, 04:45 AM   #12
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Originally Posted by bmwrench View Post
marksb'ville's memory is right, and mine was wrong. One summer in the late '70s, it seemed like all I did was rebuild unit 650/750 motors-or more accurately, replace crank bearings. Not only did we leave the gearbox internals in place, we also lefft the cam gears on.

If it hasn't been mentioned already, pull and clean the sludge trap. and repalce the rod bolts.

Wherever you are Dad, thank you.

...and be careful the rod bolts you get aren't Chinese rubbish. +1 on the sludge trap... this one was 50% blocked, but only had 100,000 miles on it, yes, that's right. My buddie and I rebuilt it last in 1980, he rode it cross country 3 times and everywhere else. Top end was wheezing, so we pulled it back down, sludge trap was the whole reason we opened the bottom.

















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concours screwed with this post 12-23-2011 at 06:15 AM
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Old 12-23-2011, 06:26 AM   #13
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Sludge trap half full was it? I used to read on the Brit Bike forum about how guys were finding their sludge traps squeaky clean in the modern era of lubricating oils, when they were going in for a look - the assumption was that the modern oils kept the crap in suspension until the next oil change. 100K miles is very impressive service life - you two must know what you're doing.
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Old 12-23-2011, 03:45 PM   #14
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[QUOTE=jackd;17577112]Sludge trap half full was it? I used to read on the Brit Bike forum about how guys were finding their sludge traps squeaky clean in the modern era of lubricating oils, when they were going in for a look - the assumption was that the modern oils kept the crap in suspension until the next oil change. 100K miles is very impressive service life - you two must know what you're doing.[/QUOTE}


That was run on Castrol 20-50 dino oil the whole way. It IS fitted with a Lockhart oil cooler. Did you notice the logo stamped on the crankshaft? That is a big reason why it lasted so long. That, and my buddy rides it gently, rather than a hammer.
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Old 12-23-2011, 04:45 PM   #15
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I really appreciate all the pics and info and will look it all over in a week or so, a family emergency came up and I'll be out of town, just did not want anyone to think I was ignoring them. Be safe for the holidays and I'll post some pics when I get back in town. Thanks Again.
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