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Hi All I recently got a 1950 T6 that has a 750 head on it and have a few questions I hope can get answered.
when was this modification popular? Im trying to estimate when the bike was modded into a chopper
what year 750 head would have been used?
and lastly for the moment im working on oil leaks and either have some oil coming from the head gasket or the
push rod tube. would I need the 750 or 650 gaskets?

Thanks for the new guy help George
720641
 

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Hi George,

Firstly, welcome to the Forum. :)

I've moved your thread to the main Classic, Vintage & Veteran Forum (you'd posted in the Vintage Technical Tips & Tricks sub-forum, which is for posting 'em, not asking for 'em. ;)). More people will see your thread in the main CVV Forum, so you're more likely to get answers.

Hth.

Regards,
 

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There really isn't a 750 "Head" per say. The larger displacement (750) is in the Cylinder Bore. If indeed it has 750 kit, it has different cylinders and pistons. Your picture shows a typical 650 head so that is likely unchanged. The "Head" from a 750 cc short rod motor in most cases has 10 head to cylinder bolts. That could be considered a 750 head but it has nothing to do with the actual displacement. The only way to know if it is 750cc is pull the head and measure the bore. .
 

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Doesn't T140 750 head have squish band machined in it? Compared to late 650 9 bolt head with the undrilled 10 bolt. I believe that head has 650 combustion chamber? The 750 10 bolt head would have reduced pinch area on gasket on 650 cyl. the way I see it.
Don
 

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Hi GDaddy, What a cool bike! Brings me back to my youth! Peanut tank, cobra seat, drag bars, tall sissy bar, spool front wheel. Someone was a really cool guy back when. Looks like you have a real survivor.

Detailed photos of motor top all around & cylinder base all around & any #s in cyl base flange will allow better identification of parts.
Don
 

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The rocker box bolts are not correct. These tend to strip the threads and many have been heli-coiled. I'd try a retorque followed by a valve lash adjustment. The bottoms of the PRT's could use a "wedding band" to keep the seal from squishing out. The cylinder base bolts are 1971 and I'd expect the whole top end is.
 

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Hi George,

The cylinder base bolts are 1971 and I'd expect the whole top end is.
(y) I knew something was wrong in your pictures, but I couldn't for the life of me think what ...

By "cylinder base bolts", Bob means the nuts and studs securing the cylinder barrel to the crankcase.

One of the things you come across on these old heaps is Triumph (and BSA) changed from British Standard threadforms to mainly Unified (UNF and UNC) threadforms over several years mainly in the late 1960's:-

. the 12-point nuts securing the cylinder base are UNF;

. the threadform on the other ends of those studs - into the crankcase - is UNC;

. however, when your 6T's crankcases were made, Triumph was the best part of twenty years away from using Unified threads, those in the crankcase are BSW - British Standard Whitworth;

. the only reason the ... ummm ... builder :rolleyes: ... was able to get away with screwing UNC-thread studs into BSW crankcase holes is the threadforms are similar (not the same) - be unsurprised to find lots of sealant on these studs into the crankcase ...

looks like a 71 or early 72 with push-in exhaust pipes
Hopefully @coloradobob will read this and clarify. The rocker-boxes are pre-'71 and, while it isn't impossible to fit pre-'71 rocker-boxes on a '71/'72 650 head, nor are they simple bolt-together. Also, aiui '71 and '72 650 heads still had spigots that screw into the exhaust ports, the pipes pushing over the spigots, the pipes being clamped to the spigots by the finned roses?

The bottoms of the PRT's could use a "wedding band" to keep the seal from squishing out.
Mmmm ... this is the lid of a large can of worms for a newbie, especially given the above.

Your close-up pictures show what's known colloquially as a "9-stud head". Each cylinder has two 3/8"-dia. studs through the rocker-boxes and cylinder head into the barrel and two 3/8"-dia bolts only through the cylinder head into the barrel, = 8, the ninth is a smaller 5/16"-dia. bolt through the cylinder head into the barrel between the cylinders.

Trouble is, that's basically every 650 cylinder head from '63 to '74 ... a "wedding band" would only be correct for '71-on or if you were upgrading '69/'70 to the later standard.

working on oil leaks and either have some oil coming from the head gasket or the push rod tube. would I need the 750 or 650 gaskets?
Afaict, it's unlikely the engine's 750 - showing in one of your close-up images is "E6305" cast into the cylinder base, that's the casting 'part number' of any standard '65-on 650 block.

However, during the above periods, Triumph used at least three different push-rod tubes ("PRT") and three different sealing arrangements on the 650 ... The first step towards (reasonably) leak-free PRT is matching cylinder head, PRT, seals and tappet guide blocks (in the cylinder barrel base) ... As the hardest- and most-expensive-to-obtain part in that list is a decent cylinder head, you might want to positively-identify what's on the engine now (and whether it's usable without too much more expense), then see which of the other listed parts on the engine now are really compatible (as opposed to "compatible" decided by someone who screws UNC male threads into BSW female threads ...).

Fasteners
Ime, be unsurprised to find most on the engine are British Standard threadforms - BSC (British Standard Cycle) into iron (e.g. cylinder head bolts/studs into the cylinder barrel) and steel (e.g. nuts on studs) components, BSW into crankcase aluminium alloy, BSF (British Standard Fine) into cylinder head/rocker-box aluminium alloy - reason for the different threadforms into ally is age, Triumph changed from BSW to BSF between about '57 and '62.

However, if @coloradobob's right about the finding the rocker-box fastener threads in the head having been stripped, they could well have been helicoiled to UNC.

Confusingly and regrettably, many of your countrymen label all British Standard threadforms just "Whitworth", (n) even through your bike likely has three different ones. However, the upside is all the different threadforms use the same wrench/socket hex. sizes. (y) Just be aware they're sized by shank diameter, not 'Across Flats' like Unified-thread or metric wrenches/sockets - e.g. although the cylinder head bolts and nuts look like about 9/16" AF, the wrench or socket that fits 'em will be labelled "3/8 BS" and "5/16 W".

The above pretty-much only applies to shank diameters 1/4" and bigger. Smaller is another threadform known as "BA" (British Association); each standard thread is denoted by a number prefixing the BA - 0BA is the largest and is a gnats under 1/4" diameter. The most common on these old heaps is 2BA - here a gnat's under 3/16" diameter, looks like 10-32 and M5 but it is not the same.

Hth.

Regards,
 

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Discussion Starter #12
The rocker box bolts are not correct. These tend to strip the threads and many have been heli-coiled. I'd try a retorque followed by a valve lash adjustment. The bottoms of the PRT's could use a "wedding band" to keep the seal from squishing out. The cylinder base bolts are 1971 and I'd expect the whole top end is.
Thanks for the help Coloradobob
 

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Discussion Starter #13
Hi George,


(y) I knew something was wrong in your pictures, but I couldn't for the life of me think what ...

By "cylinder base bolts", Bob means the nuts and studs securing the cylinder barrel to the crankcase.

One of the things you come across on these old heaps is Triumph (and BSA) changed from British Standard threadforms to mainly Unified (UNF and UNC) threadforms over several years mainly in the late 1960's:-

. the 12-point nuts securing the cylinder base are UNF;

. the threadform on the other ends of those studs - into the crankcase - is UNC;

. however, when your 6T's crankcases were made, Triumph was the best part of twenty years away from using Unified threads, those in the crankcase are BSW - British Standard Whitworth;

. the only reason the ... ummm ... builder :rolleyes: ... was able to get away with screwing UNC-thread studs into BSW crankcase holes is the threadforms are similar (not the same) - be unsurprised to find lots of sealant on these studs into the crankcase ...


Hopefully @coloradobob will read this and clarify. The rocker-boxes are pre-'71 and, while it isn't impossible to fit pre-'71 rocker-boxes on a '71/'72 650 head, nor are they simple bolt-together. Also, aiui '71 and '72 650 heads still had spigots that screw into the exhaust ports, the pipes pushing over the spigots, the pipes being clamped to the spigots by the finned roses?


Mmmm ... this is the lid of a large can of worms for a newbie, especially given the above.

Your close-up pictures show what's known colloquially as a "9-stud head". Each cylinder has two 3/8"-dia. studs through the rocker-boxes and cylinder head into the barrel and two 3/8"-dia bolts only through the cylinder head into the barrel, = 8, the ninth is a smaller 5/16"-dia. bolt through the cylinder head into the barrel between the cylinders.

Trouble is, that's basically every 650 cylinder head from '63 to '74 ... a "wedding band" would only be correct for '71-on or if you were upgrading '69/'70 to the later standard.


Afaict, it's unlikely the engine's 750 - showing in one of your close-up images is "E6305" cast into the cylinder base, that's the casting 'part number' of any standard '65-on 650 block.

However, during the above periods, Triumph used at least three different push-rod tubes ("PRT") and three different sealing arrangements on the 650 ... The first step towards (reasonably) leak-free PRT is matching cylinder head, PRT, seals and tappet guide blocks (in the cylinder barrel base) ... As the hardest- and most-expensive-to-obtain part in that list is a decent cylinder head, you might want to positively-identify what's on the engine now (and whether it's usable without too much more expense), then see which of the other listed parts on the engine now are really compatible (as opposed to "compatible" decided by someone who screws UNC male threads into BSW female threads ...).

Fasteners
Ime, be unsurprised to find most on the engine are British Standard threadforms - BSC (British Standard Cycle) into iron (e.g. cylinder head bolts/studs into the cylinder barrel) and steel (e.g. nuts on studs) components, BSW into crankcase aluminium alloy, BSF (British Standard Fine) into cylinder head/rocker-box aluminium alloy - reason for the different threadforms into ally is age, Triumph changed from BSW to BSF between about '57 and '62.

However, if @coloradobob's right about the finding the rocker-box fastener threads in the head having been stripped, they could well have been helicoiled to UNC.

Confusingly and regrettably, many of your countrymen label all British Standard threadforms just "Whitworth", (n) even through your bike likely has three different ones. However, the upside is all the different threadforms use the same wrench/socket hex. sizes. (y) Just be aware they're sized by shank diameter, not 'Across Flats' like Unified-thread or metric wrenches/sockets - e.g. although the cylinder head bolts and nuts look like about 9/16" AF, the wrench or socket that fits 'em will be labelled "3/8 BS" and "5/16 W".

The above pretty-much only applies to shank diameters 1/4" and bigger. Smaller is another threadform known as "BA" (British Association); each standard thread is denoted by a number prefixing the BA - 0BA is the largest and is a gnats under 1/4" diameter. The most common on these old heaps is 2BA - here a gnat's under 3/16" diameter, looks like 10-32 and M5 but it is not the same.

Hth.

Regards,
Thanks for all of the info StuartMac
Looks like im going to be spending a bit of time bugging my local Triumph shop with quite a few trips to get this fully sorted out. Also thanks for the excellent explanation on the British threads its going to be a huge help.

On the cylinder base bolts is it possible that the bolt holes were heicoiled not sure if they were even available in the early 70s..

And to recap my items to sort out

Facts my cylinders are 65 and up, heads are 650 9 hole 71-72, rocker boxs are pre 71

1 cylinder base bolts source proper BSW bolts or confirm if UNC helicoils were installed in cases.
2 source head gasket 650
what years head gasket should I use?
3 confirm if heads were helicoiled to UNC or source proper fasteners
4 sort out the PRT seals

Again Thanks for all the great info
 

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Don't all heads have a casting year inside the rocker area? With a clockface to indicate which month?
 

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Hi George,

cylinder base bolts is it possible that the bolt holes were heicoiled
items to sort out
1 cylinder base bolts source proper BSW bolts or confirm if UNC helicoils were installed in cases.
When you get as far as taking the barrel off, I can offer suggestions for a stud remover; remove one and it'll be easy to tell if it's been helicoiled.

If the holes haven't been helicoiled and you want to replace the incorrect UNC/-UNF-thread studs, the replacements will also be studs, there isn't enough room between the holes, fins and barrel casting for bolt heads. However, the nut thread on these replacement studs will be BSC, for which you'll need BSC nuts; these'll be what's known as "small hex." - instead of them having a hex. that, say, a "3/8 BS" wrench'll fit, you'll use a "5/16 BS" wrench; fwiw, you'll find this quite often on old Britbikes that have British Standard threads.

Aside: years ago, the-then girlfiend acquired a Britbike bitsa that had British Standard fasteners. Obviously since the original toolkit was long-gone, and the advertised "one careful owner" had been in amongst several uncareful ones ... :rolleyes: it took me a while to appreciate why the parts book listed different-part number nuts on each end of many studs - one was a 'small hex.' nut, the other was a 'normal hex.' nut - so they could be loosened/tightened with different-size wrenches, so two wrenches of the same size weren't necessary in the original toolkit. (y)

items to sort out
my cylinders are 65 and up, heads are 650 9 hole 71-72, rocker boxs are pre 71
2 source head gasket 650
what years head gasket should I use?
I'm not sure the head is '71/'72; they had dowels to 'stake' the rocker-boxes - to stop the various heating-cooling cycles 'shuffling' the boxes around, which led to leaks from those joints. Obviously the dowels could be removed to allow earlier rocker-boxes to be fitted but ... As I posted earlier, I'm hoping Bob (or someone else) will post more information.

The head gasket itself is much of a muchness - I like and have used solid copper for years because, having made the initial purchase of one on the bike and one off, the one removed any time for whatever reason can be annealed and kept as the "one off" the bike for the next changeover. (y)

If you like this idea:-

. on the one hand similar copper (and aluminium) gaskets are available for the crankcase-barrel and head-rocker-box joints; (y)

. otoh, each pair of joint surfaces will have to be prepared carefully certainly the first time you use these gaskets and maybe a few times depending how bad the PO were; (n) however, once the gaskets do seal properly, all you have to do is not damage them or the component sealing surfaces for them to continue sealing. :)

Otoh2, if the crankcase-barrel or head-rockerbox joints would take more time and or money to fix than you can spend, consider "CovSeal" gaskets. These are an invention by John Healy, owner of US parts wholesaler Coventry Spares; only bear in mind CS being a wholesaler, they'll only tell you which retailers they supply.

4 sort out the PRT seals
You can buy (allegedly) complete sets of gaskets and seals - usually either 'top end' or 'complete'. I'm not a fan because they rarely are "complete" - either due to cock-up or conspiracy - they always lack tab washers, they never have copper gaskets, I'll bugger something there isn't a spare of, etc., etc. :( Plus the 650 versions (attempt to) include every different PRT seal variation.

Imho, this is why it's important first to identify the head's year(s) - the PRT and sealing are different and not interchangeable, certainly if you don't want frequent leaks/fixing. Who is/are your "local Triumph shop"? If they're any good, they should be able to date the head and tell you what, if any, work it needs - no point matching PRT, tappet guide blocks and seals only to find the head needs major expense?

Btw, you might be told the head is "bowed" or similar; curiously, despite the apparent solidity of the head casting, they're relatively easy to bend, usually across the PRT. But for the same reason, don't allow the gasket surfaces to be ground flat to 'straighten' the head; if it's easy to bend one way, it's equally easy to bend it back again? :) Once the head is flat, when you reassemble, we can initiate you into the arcane rite of Measuring The Squish ... :LOL:

More prosaically, once the head is dated, you can go to one of the online parts books indexes - e.g. Vintage Bike Magazine » Parts Books - look up the one applicable to the head and see the PRT and seals your engine's top-end should have. Another handy reference for checking PRT is http://vintagebikemagazine.com/wp-content/uploads/2017/04/pushrodtubes1.jpg

Finally here, again if your local Triumph shop is any good, they should be able to tell you if the tappet guide blocks in the barrel are usable with the head, PRT and seals - risking stating the obvious, because the bottom PRT seal seals on the TGB.

Hth.

Regards,
 

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Hi GDaddy, I've found over the years, if you can get motor started & bike driving as is you will learn what it's doing & evaluate how the clutch, trans & all that work. I recommend doing that if possible.

In the mean time you'll learn about the carbs, ect. I try to spend the least as possible to get it running, but you'll need some parts to just get it started. If your gas tank has rust at all in it get some of the little plastic filters with paper elements. The do good job to keep rust out until tank is properly cleaned.

Even a 20 mile ride will tell you a whole lot. It takes at least that much to heat soak motor. The motors change a lot between cold start, 3 miles & 20 miles. The heat soaking is the real test. Been down this road enough times.

Aged tires can blow, but as/more importantly they have very poor traction, almost like rubber is hard plastic. Will throw you down faster than you can move your foot. Remember most stopping power is front brake, so be careful!

Well sorted these bikes are good runners & very reliable, they really are.
Don
 

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Hmmm,been a long time since I had a 53 6T with a unit upper end..but..I have two 56 650 engines and both have engine cases that accept 3/8-16 cylinder hold down studs .....
 

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Hi Tony,

have two 56 650 engines and both have engine cases that accept 3/8-16 cylinder hold down studs ...
3/8"-16 is both UNC and BSW, it's likely personal preference and experience that says whether a UNC-thread stud is OK in a BSW -threaded crankcase hole?

My personal preference in a similar situation would be to use BSW-thread cylinder hold down studs, if only because (almost?) all the other engine fasteners are also British Standard threads, and those studs would then have BSC-thread nuts on the other ends.

Regards,
 

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Discussion Starter #19
Hi GDaddy, I've found over the years, if you can get motor started & bike driving as is you will learn what it's doing & evaluate how the clutch, trans & all that work. I recommend doing that if possible.

In the mean time you'll learn about the carbs, ect. I try to spend the least as possible to get it running, but you'll need some parts to just get it started. If your gas tank has rust at all in it get some of the little plastic filters with paper elements. The do good job to keep rust out until tank is properly cleaned.

Even a 20 mile ride will tell you a whole lot. It takes at least that much to heat soak motor. The motors change a lot between cold start, 3 miles & 20 miles. The heat soaking is the real test. Been down this road enough times.

Aged tires can blow, but as/more importantly they have very poor traction, almost like rubber is hard plastic. Will throw you down faster than you can move your foot. Remember most stopping power is front brake, so be careful!

Well sorted these bikes are good runners & very reliable, they really are.
Don
Thanks and yes i did get the bike running but just a trip around the block.
the rims and tire are beyond dangerous and ive already removed them and dropped them off for repair and new tires.
The real only major issues I see are oil and fuel leaks but I would also like to make sure the other issues are sorted out for peace of mind while im out riding break downs suck.
 

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Discussion Starter #20
Hi George,


When you get as far as taking the barrel off, I can offer suggestions for a stud remover; remove one and it'll be easy to tell if it's been helicoiled.

If the holes haven't been helicoiled and you want to replace the incorrect UNC/-UNF-thread studs, the replacements will also be studs, there isn't enough room between the holes, fins and barrel casting for bolt heads. However, the nut thread on these replacement studs will be BSC, for which you'll need BSC nuts; these'll be what's known as "small hex." - instead of them having a hex. that, say, a "3/8 BS" wrench'll fit, you'll use a "5/16 BS" wrench; fwiw, you'll find this quite often on old Britbikes that have British Standard threads.

Aside: years ago, the-then girlfiend acquired a Britbike bitsa that had British Standard fasteners. Obviously since the original toolkit was long-gone, and the advertised "one careful owner" had been in amongst several uncareful ones ... :rolleyes: it took me a while to appreciate why the parts book listed different-part number nuts on each end of many studs - one was a 'small hex.' nut, the other was a 'normal hex.' nut - so they could be loosened/tightened with different-size wrenches, so two wrenches of the same size weren't necessary in the original toolkit. (y)


I'm not sure the head is '71/'72; they had dowels to 'stake' the rocker-boxes - to stop the various heating-cooling cycles 'shuffling' the boxes around, which led to leaks from those joints. Obviously the dowels could be removed to allow earlier rocker-boxes to be fitted but ... As I posted earlier, I'm hoping Bob (or someone else) will post more information.

The head gasket itself is much of a muchness - I like and have used solid copper for years because, having made the initial purchase of one on the bike and one off, the one removed any time for whatever reason can be annealed and kept as the "one off" the bike for the next changeover. (y)

If you like this idea:-

. on the one hand similar copper (and aluminium) gaskets are available for the crankcase-barrel and head-rocker-box joints; (y)

. otoh, each pair of joint surfaces will have to be prepared carefully certainly the first time you use these gaskets and maybe a few times depending how bad the PO were; (n) however, once the gaskets do seal properly, all you have to do is not damage them or the component sealing surfaces for them to continue sealing. :)

Otoh2, if the crankcase-barrel or head-rockerbox joints would take more time and or money to fix than you can spend, consider "CovSeal" gaskets. These are an invention by John Healy, owner of US parts wholesaler Coventry Spares; only bear in mind CS being a wholesaler, they'll only tell you which retailers they supply.


You can buy (allegedly) complete sets of gaskets and seals - usually either 'top end' or 'complete'. I'm not a fan because they rarely are "complete" - either due to cock-up or conspiracy - they always lack tab washers, they never have copper gaskets, I'll bugger something there isn't a spare of, etc., etc. :( Plus the 650 versions (attempt to) include every different PRT seal variation.

Imho, this is why it's important first to identify the head's year(s) - the PRT and sealing are different and not interchangeable, certainly if you don't want frequent leaks/fixing. Who is/are your "local Triumph shop"? If they're any good, they should be able to date the head and tell you what, if any, work it needs - no point matching PRT, tappet guide blocks and seals only to find the head needs major expense?

Btw, you might be told the head is "bowed" or similar; curiously, despite the apparent solidity of the head casting, they're relatively easy to bend, usually across the PRT. But for the same reason, don't allow the gasket surfaces to be ground flat to 'straighten' the head; if it's easy to bend one way, it's equally easy to bend it back again? :) Once the head is flat, when you reassemble, we can initiate you into the arcane rite of Measuring The Squish ... :LOL:

More prosaically, once the head is dated, you can go to one of the online parts books indexes - e.g. Vintage Bike Magazine » Parts Books - look up the one applicable to the head and see the PRT and seals your engine's top-end should have. Another handy reference for checking PRT is http://vintagebikemagazine.com/wp-content/uploads/2017/04/pushrodtubes1.jpg

Finally here, again if your local Triumph shop is any good, they should be able to tell you if the tappet guide blocks in the barrel are usable with the head, PRT and seals - risking stating the obvious, because the bottom PRT seal seals on the TGB.

Hth.

Regards,
Thanks again for the wealth of information
 
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