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Notes from my engine builder

3K views 20 replies 9 participants last post by  Rob Axel 
#1 ·
Always knew that my bike, 500 pre unit Triumph, was made up from many different bikes but always thought the engine was a 5T bottom end with alloy barrels and head. As far as I know it was put together in the 80s and the engine hasn't been touched since then.

No real questions, I'm going with what he recommends, thought it might make interesting reading.

''Getting there with your engine.
It's a bit of a bitsa!
Turns out the crank is actually a 650 crank which explains why I had so much problem getting a sludge tube to fit.
These casings are not really ideal for a 650 crank as the timing side main bearing crank journal is 1.1/8" diameter but the casing is only designed for 1" cranks. The roller bearing, as was fitted, is not the correct size as it is not as deep as it should be but has been spaced out and made to fit.
There are no bearings available (or probably ever have been) that should be fitted here but as it worked in the past it will have to stay that way.

Another area of interest is that the 650 cranks have a stroke 2mm longer than the 500. This explains why the pistons poke above the barrel higher than they should. Again, it seems to work okay but you could never fit high compression pistons I would have thought. By the way these ones are standard comp at 7:1.

It's looking good now that the barrels and head have been repaired and bead blasted.
I will get it finished probably tomorrow.''
 
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#6 ·
Those don't sound like the words of any engine builders I've ever known.

"Seems to be OK" is an odd one. Those that taught me always said "Don't think, know!" as they pulled a dial caliper or micrometer out of their shirt pocket.

I'd expect real numbers for piston pin height and rod length, and some explanation about how the pistons have managed to not crash the valves or the head with 2mm (huge!) of extra protrusion.

Could just be lost in translation and your builder knows his business, but it sounds suspicious here with the limited facts we have.

Old Triumph cranks are plentiful and relatively cheap. No need to go to great pains to make your current parts work when you could do it correctly for a few hundred more. It's worth discussing with your builder, assuming it's not already buttoned up.

Does the build come with a spec sheet? Work guaranteed?

Jason
 
#7 ·
I don't know anyone that would even concider garentee a motor with parts that were never intentionally designed to be used together...
Im sure he will garentee his work, but as for the reliability ... unless he has been building these motors for years and KNOWS what combination of parts "work"... I betting your gonna get the "I'll garentee it as long as it runs"...
There is a reason stuff like this is called "experimental"..
I will give it to your builder.... most wouldn't even touch that motor, let alone rebuild it
 
#9 ·
Not saying it hasn't been done..hell, I'm still holding out for another shop to do a "long rod kit" for small block fords... Speed-o-motive, did it and well.. but unfortunitly they no longer exist... (Rod to stroke ratio 2to 1 parasitic drag minimized).
I don't believe I could find a shop to put together this "set up" and then ask .."will you GARENTEE this motor??.....
Last time I checked "the internet" .., there was a guy who "disappeared" after building a motor that ran on water...
You have to be careful of what you read.. YES, a lot is true, good stuff.. AND VERY informative ..but then there is the rest of it...
 
#11 · (Edited)
Thanks everyone for replies.

The engine builder I trust 100%, been there before and know a lot of others that have been there. Services go from engine rebuilds to full restorations. Very highly regarded up here, never heard even one bad comment about them.

Also he isn't building it up from odd bits I've given him. This was an engine that was running in my bike and has been for about 30 years without any problems. It was starting to get a bit tired so I took it up for a stripdown, checkover and rebuild.

Will let you know how things go.
 
#12 ·
...your mechanic sounds pretty good for me; like a real guy not a techie guru; seems he knows how translate the techie stuff into normal words for the general public.

Hi Jason Mcelroy, the old pre unit 500 cranks in usable condition ARE in fact scarce and as mentioned the bearing just do not fit so possibly the cases do not accept now those other bearings.
Then if you use these other cranks you cannot use the 650 con rods or you need to do "oversized" shell bearings.

May be you are confused with old but not so old Triumphs.
 
#13 ·
Hi Reverb,
That's exactly as I see him. He always gives me options of what in his opinion is reusable along with a price if I do want to go for new parts. Always says what bits must be replaced. Never pushes me into going for expensive new parts if it's not needed.
 
#15 ·
From the responses to my post, I must have sounded like I was shitting on your engine builder.

That was not my intent. I thought I had made that clear, but perhaps not.

Please understand that it's difficult for us here to take the information we're given and offer anything resembling reasonable advice. But we try anyway.

My intention was just to point out some things from your original post that caught my attention. Of course, I can only base these observations on my own experiences, which may differ significantly from yours or anyone else's.

One of the ways I was fortunate as a 19 year old boy building my first bike (1971 sportster) was that I came across some good teachers and mentors. One of the lasting lessons I learned (thanks, Dick) was to get out of the business of guessing and making judgement calls and into the business of science. Measuring, comparing against published specs, considering in relation to machine and engineering practices. In short, a firm basis for decision rather than an estimation. Of course this is not possible in the absolute, but it's a good way to lean. Surely many of you have met the Harley voodoo practitioner with all kind of sage advice on how to do things that sound more like old wives tales than sound logic. I know I did . . . and it left me pushing my bike along barren upstate NY country roads. I chose to value the engineering approach in response. This does not make me, or the mentors that taught me "techie gurus", it's just the lens we've chosen to guide our craft.

On the few occasions where I paid someone else to do bike work for me, I was maddened by the lack of clear explanation for what the problems were and how they intended to address them. I didn't wan't comforting language, I wanted details that I could consider and agree or disagree with. Being told that something "should work" or "don't worry about it, I'm an expert" never did it for me. If that makes me a cynic or a hard case, so be it. Had enough of being fucked over or played by so called experts and "the greats" who did shoddy work leaving me hanging.

To make a long story longer, as a good friend always says, I just wanted to clarify.

I wasn't claiming your builder doesn't know what's up. I would never be so arrogant. I was only trying deconstruct the facts you gave in hopes of giving you some direction on which questions to ask going forward.

BTW, I'm as fluent in "making due" as i am in "by the book". One thing I do in every case is make sure whatever I'm trying is well-considered and sound in principle.

Sounds like your guy may also be.

Sorry for any offense offered.

Jason
 
#17 ·
Hi Jason, I can see where you're coming from, it isn't in 'engineer' language. It wasn't a dig at you, sorry if it sounded that way.

Thunderbird, all is ok, just waiting to hear back that the engine is finished.

I'm going with the view that if it ran for 30 years with that crank/bearing whoever put it together in the first place knew what they were doing.

There's an article in a 2008 (Back Street Heroes) magazine about the bike, it's a bit vague and doesn't mention a 650 crank, presumably they didn't know. But seems it was Ray Chase (sadly no longer with us), a Triumph dealer in Ripon Yorkshire who put the bike together in it's present combination in the 1980's. That's it's date of registration on V5 docs.
 
#18 ·
The odd sized timing side bearing may be the result of matching small bearing cases with an early unit crank. The bearing used to do this is narrower and a spacer is required to take up crank end float, spacer is 1/8 inch thick I think. The crank conversion then gives you replaceable bigend bearings on the conrods.
If you search the site for Triumph crankshafts you will find a better description.
Torry
 
#21 ·
One thing I have learned with these old Britt motors..they are not the most "highly Machined" motor... so there is a lot of tolerance...very forgiving. And one could argue a good platform to "exparament" on....
.. hence, the current discussion...
I don't claim to know a lot about engine building, I know just enough to get myself in trouble and get my lawnmower running in the spring....
... and 99% of what I have learned about 650s was from this site and others..
Let's keep the information alive...
 
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