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Discussion Starter #1 (Edited)
Dear Triumph Elders and Sages-

I need a head replacement for my TR6. I have located a possible candidate but the threads on at least one of the the exhaust spigots can't be saved. By all appearances, everything else on the head looks servicable: good mating surface (that hasn't been milled down), the valve seats profile looks OK, there are no apparent cracks or fin breakage and waiting on confirmation for the remainder of the threads.

My question is should I stay away from this head, or can the exhaust spigot threads be easily restored at a reasonable cost?

Also looking at another one with what appears to be a poor spark plug thread repair job.

Thanks in advance.

Jeff
 

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The spark plug repair would be the cheaper option but exhaust threads are a common repair also. Either head would be OK to repair.
 

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Discussion Starter #3
The spark plug repair would be the cheaper option but exhaust threads are a common repair also. Either head would be OK to repair.
Thanks Rambo. What would I expect to pay for something like that?
 

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If the spigots are solid on the other head and the only repair will be to the spark plug thread then I'd go for that one. Before you decide try contacting Seager Engineering in the UK for a price for the exhaust spigot thread repair. You may not want to send it here but it shows what can be done (see gallery) and it'll give you an idea of the cost. They also manufacture oversize spigots and sell via e-bay, if there's enough thread left these can work. I'm using two +0.005" spigots at the moment screwed in with high temperature silicon sealant and though they did loosen again when I had to twist off the exhaust pipes in service they seem secure.


Chris
 

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Discussion Starter #5
If the spigots are solid on the other head and the only repair will be to the spark plug thread then I'd go for that one. Before you decide try contacting Seager Engineering in the UK for a price for the exhaust spigot thread repair. You may not want to send it here but it shows what can be done (see gallery) and it'll give you an idea of the cost. They also manufacture oversize spigots and sell via e-bay, if there's enough thread left these can work. I'm using two +0.005" spigots at the moment screwed in with high temperature silicon sealant and though they did loosen again when I had to twist off the exhaust pipes in service they seem secure.


Chris
Great info, thanks Chris, and thanks for the link!
 

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What year is your TR6? there were changes at model year '69 (deeper pushrod tube sockets) and '71 (dowelled and cutaway rocker boxes). The casting date in the valve spring pocket area (typically 68 for a '69 model give a clue for the first change, ut Triumph stopped using the casting date later, so you need to look for the dowel holes.
HTH
 

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Both threads are not expensive to have repaired. I just had an exhaust port thread repair done to a Triumph Tiger Cub head. I can't tell you exactly how much it cost, because I also had the valves, springs and guides replaced, along with the valve seats being cut, and fixed some broken fins, etc. The whole job was only $270. The guy that did the repair for me does this kind of repair all the time. He is a well respected machinist. He is here in Pennsylvania. Long's Custom Mechanical Services. 610-286-5870

Hope that helps.

Rob
 

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Discussion Starter #8
What year is your TR6? there were changes at model year '69 (deeper pushrod tube sockets) and '71 (dowelled and cutaway rocker boxes). The casting date in the valve spring pocket area (typically 68 for a '69 model give a clue for the first change, ut Triumph stopped using the casting date later, so you need to look for the dowel holes.
HTH
Hey Mick, it's a '68.

My understanding is that any head with a casting stamp of 66-68 would be suitable for a '68 model year (and PRT depth). The problem is the nuanced reading the tick marks, because potentially a head with a '66 stamp could be used for a '66 or '67 model year.
 

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You could go new for almost 1000 and still need valves and springs.

Or used like Mitch here has.

Mind you Mitch superseded the 1968 number to 69-70. I think it would work but I couldn't be sure without installing it.
If used on pre 68 engine the tappet guide blocks and pushrod tubes have to be changed as well.
 

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Hey ****, it's a '68.

My understanding is that any head with a casting stamp of 66-68 would be suitable for a '68 model year (and PRT depth). The problem is the nuanced reading the tick marks, because potentially a head with a '66 stamp could be used for a '66 or '67 model year.
I would be careful of a 68 casting, the model year for '69 changed in Autumn '68. It is obvious enough that the "socket" for the PRT is much deeper on the later head, just be sure to check rather than believe what you're told!
Good luck in the hunt.
 

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Hi Jeff,
Or used like Mitch here has.
http://www.klempfsbritishparts.com/HEAD--CYL--TR6--69-70-0
Mind you Mitch superseded the 1968 number to 69-70. I think it would work but I couldn't be sure without installing it.
If used on pre 68 engine the tappet guide blocks and pushrod tubes have to be changed as well.
I would be careful of a 68 casting, the model year for '69 changed in Autumn '68. It is obvious enough that the "socket" for the PRT is much deeper on the later head, just be sure to check rather than believe what you're told!
Uh-uh, the change is '68-to-'69, and the '69 model year began in July 1968.

'69-on heads have smaller-ID PRT holes than pre-'69 - 1.140" vs. 1.250" according to John Healy.

It isn't impossible to use a '69-on head on a pre-'69 engine but not only must you to change tappet guide blocks, PRT and seals (as @Stacy Slay posted), then you potentially become embroiled in the part-way-through-'70 'fix' :ROFLMAO: of adding one of the pre-'69 white seals back in between TGB and PRT, plus the 'wedding bands' to stop those seals being squeezed out ... :eek: the pre-'69 PRT sealing is by no means perfect but '69-on is a can of worms afaict.

Hth.

Regards,
 

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Hi Jeff,


Uh-uh, the change is '68-to-'69, and the '69 model year began in July 1968.

'69-on heads have smaller-diameter PRT holes than pre-'69 - 1.140" vs. 1.250" according to John Healy.

It isn't impossible to use a '69-on head on a pre-'69 engine but not only must you to change tappet guide blocks, PRT and seals (as @Stacy Slay posted), then you potentially become embroiled in the part-way-through-'70 'fix' :ROFLMAO: of adding one of the pre-'69 white seals back in between TGB and PRT, plus the 'wedding bands' to stop those seals being squeezed out ... :eek: the pre-'69 PRT sealing is by no means perfect but '69-on is a can of worms afaict.

Hth.

Regards,
The important bit I was trying to get across is that a 68 casting mark is highly likely to be a '69 model head, it is much easier to "see" the difference in depth of the PRT holes between the two heads, especially if you have an original, knackered, 68 model head for comparison, as does Jeff
 

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Discussion Starter #13 (Edited)
Just to be clear, the head that came with my '68 TR6P has a date stamp of 62+, so it clearly is not the original head.

I just measured the PRT that came off of my girl and the measurements match up with part number 70-6000 (as shown in the Healy article), for model years 65-67, which presumably would be incompatible with my '62 head or any other future replacement head outside of model year '66?

I was a little disappointed to see that John Healy article does not go into any great depth or make a one-to-one correlation between PRT year and alloy head year by date stamp (or model year), which has always been a bone of contention for me a source of extreme vexation.
 

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Take a look at the JRC guide, with the John Healy stuff, it just about covers it. Some of the PRT part number changes were to do with construction and piercings at the top, and don't affect function, so don't get TOO hung up on the numbers.
HTH
 

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Hi Jeff,
measured the PRT that came off of my girl and the measurements match up with part number 70-6000 (as shown in the Healy article), for model years 65-67, which presumably would be incompatible with my '62 head or any other future replacement head outside of model year '66?

the head that came with my '68 TR6P has a date stamp of 62+, so it clearly is not the original head.
(n) 'Fraid you aren't extrapolating correctly.

Your bike's cylinder head "date stamp of 62+" simply indicates it was cast some time during the 1962 calendar year.

Significantly, 650's changed from pre-unit to unit from the '63 model year, so during the 1962 calendar year. Aiui, one of the pre-unit-to-unit changes was the ninth bolt through the cylinder head into the block, between the bores? If so, and your bike's head/block has the ninth bolt, your bike does not have a "'62 [model year] head", it must be a '63 model year or later unit head.

On a complex part like a cylinder head, the difference between a casting and a part ready to be built into an engine is the machining of the casting - pre-unit and unit 650 heads might be the same casting (with "a date stamp of 62+") but the casting would be machined differently depending whether the finished part was intended for pre-unit or unit engines.

Then why would "part number 70-6000 (as shown in the Healy article), for model years 65-67 ... be incompatible with [your '63-on(?)] head or any other future replacement head outside of model year '66?" :confused:

Firstly, digressing slightly but importantly, in the Healy article, afaict "1967" under 70-6000 and "1968" under 70-9349 are misprints. The PRT changes coincide with the change from pre-'69 70-3547 white oblong-section seal to the '69-on O-rings (70-7310 superseded by 71-1283) and, as the texts under the article's two cylinder head images say, the seals change happened '68-'69 and what M'ick called 'the "socket" for the PRT' changes ID significantly.

So afaict, "part number 70-6000 (as shown in the Healy article)" should read, "650cc 'B' Range 1965 to 1968".

So, unless your bike has an 8-bolt head, you're looking at a '63-'68 unit 650 head and '65-'68 PRT.

Then the difference between alleged PRT lengths - pre-'65 70-3646 and '65-'68 70-6000 - is only 0.070". For '65, Meriden went from pre-'65 different 'white seals' top and bottom to '65-'68 the same 70-3547 'white seal' top and bottom - 70-3547 is ~1/10" (+-0.1000) thick, the superseded 70-1476 is ~3/16" (+-0.1875") thick, the 0.0875" difference being remarkably similar to the the difference in alleged PRT lengths? ;)

So, if your bike has 70-6000 PRT and the same-thickness (and -ID and -OD) white seals, the total height of PRT and seals isn't any different from 70-3646 PRT and different white seals; either combination works with any pre-'69 unit 650 head.

And, in the unlikely event your bike somehow does have a '62-model-year pre-unit head, exactly the same 70-3646 PRT-and-different-white-seals were fitted to them too. :)

a little disappointed to see that John Healy article does not go into any great depth or make a one-to-one correlation between PRT year and alloy head year by date stamp (or model year), which has always been a bone of contention for me a source of extreme vexation.
John Healy is at least Coventry Spares, Podtronics and Tympanium; supplying retailers is what pays his bills; at past eighty years old, I suspect he probably likes some 'me' time too ...

Hth.

Regards,
 

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Discussion Starter #16
Take a look at the JRC guide, with the John Healy stuff, it just about covers it. Some of the PRT part number changes were to do with construction and piercings at the top, and don't affect function, so don't get TOO hung up on the numbers.
HTH
By chance I discovered the JRC guide and that cleared up a lot of the ambiguity for me. It seems the PRT I have is correct for years 66-68, and that if I did not want to be a stickler, I could continue using my late '62 head, but ...
 

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Discussion Starter #17 (Edited)
Hi Jeff,

(n) 'Fraid you aren't extrapolating correctly.

Your bike's cylinder head "date stamp of 62+" simply indicates it was cast some time during the 1962 calendar year.

Significantly, 650's changed from pre-unit to unit from the '63 model year, so during the 1962 calendar year. Aiui, one of the pre-unit-to-unit changes was the ninth bolt through the cylinder head into the block, between the bores? If so, and your bike's head/block has the ninth bolt, your bike does not have a "'62 [model year] head", it must be a '63 model year or later unit head.

On a complex part like a cylinder head, the difference between a casting and a part ready to be built into an engine is the machining of the casting - pre-unit and unit 650 heads might be the same casting (with "a date stamp of 62+") but the casting would be machined differently depending whether the finished part was intended for pre-unit or unit engines.

Then why would "part number 70-6000 (as shown in the Healy article), for model years 65-67 ... be incompatible with [your '63-on(?)] head or any other future replacement head outside of model year '66?" :confused:

Firstly, digressing slightly but importantly, in the Healy article, afaict "1967" under 70-6000 and "1968" under 70-9349 are misprints. The PRT changes coincide with the change from pre-'69 70-3547 white oblong-section seal to the '69-on O-rings (70-7310 superseded by 71-1283) and, as the texts under the article's two cylinder head images say, the seals change happened '68-'69 and what M'ick called 'the "socket" for the PRT' changes ID significantly.

So afaict, "part number 70-6000 (as shown in the Healy article)" should read, "650cc 'B' Range 1965 to 1968".

So, unless your bike has an 8-bolt head, you're looking at a '63-'68 unit 650 head and '65-'68 PRT.

Then the difference between alleged PRT lengths - pre-'65 70-3646 and '65-'68 70-6000 - is only 0.070". For '65, Meriden went from pre-'65 different 'white seals' top and bottom to '65-'68 the same 70-3547 'white seal' top and bottom - 70-3547 is ~1/10" (+-0.1000) thick, the superseded 70-1476 is ~3/16" (+-0.1875") thick, the 0.0875" difference being remarkably similar to the the difference in alleged PRT lengths? ;)

So, if your bike has 70-6000 PRT and the same-thickness (and -ID and -OD) white seals, the total height of PRT and seals isn't any different from 70-3646 PRT and different white seals; either combination works with any pre-'69 unit 650 head.

And, in the unlikely event your bike somehow does have a '62-model-year pre-unit head, exactly the same 70-3646 PRT-and-different-white-seals were fitted to them too. :)


John Healy is at least Coventry Spares, Podtronics and Tympanium; supplying retailers is what pays his bills; at past eighty years old, I suspect he probably likes some 'me' time too ...

Hth.

Regards,
Hi Stu, as I mentioned above, the JRC guide set me on the right footing after walking away from the Healy article feeling a bit punch drunk. I should have been more specific and instead of calling out 62+, emphasized 'late '62' head, with 9 bolts.

From what I have surmised, the PRT recess (1/32 in) in the head is identical for all late '62 through mid '68 heads, so I can use any of these date stamped years with the PRT (70-6000) that just came out of service, and ideally stay with the tappets, guide block and o-rings correct for my model year, just so there is no second guessing during regular service intervals when it comes time to replace consumable parts, but I hear what you are saying about "either combination works with any pre-'69 unit 650 head."

Can you explain what is meant by 'B' Range? I am not quite getting that since all referenced PRT fall under that category.

Also, I see that aftermarket alloy (vs chromed) alternatives are available, and though while lacking the rich finish of the chrome, would be corrosion resistant. I am wondering if people have had good luck with those?

Thanks.
 

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Hi Stu, as I mentioned above, the JRC guide set me on the right footing after walking away from the Healy article feeling a bit punch drunk. I should have been more specific and instead of calling out 62+, emphasized 'late '62' head, with 9 bolts.

From what I have surmised, the PRT recess (1/32 in) in the head is identical for all late '62 through mid '68 heads, so I can use any of these date stamped years with the PRT (70-6000) that just came out of service, and ideally stay with the tappets, guide block and o-rings correct for my model year, just so there is no second guessing during regular service intervals when it comes time to replace consumable parts, but I hear what you are saying about "either combination works with any pre-'69 unit 650 head."

Can you explain what is meant by 'B' Range? I am not quite getting that since all referenced PRT fall under that category.

Also, I see that aftermarket alloy (vs chromed) alternatives are available, and though while lacking the rich finish of the chrome, would be corrosion resistant. I am wondering if people have had good luck with those?

Thanks.
"B" range = 650 and 750 twins, "C" range are the 350 and 500 unit twins. I don't know if there was ever an "A" range!
I do use the alloy PRT's on specials, but they still corrode, just differently. On of the great things about leaks is that it stops corrosion! I have found that I have had to skim the OD of the lower part of the PRT a couple of times to clear the late "wedding bands", but it is useful to be able to modify the length of the tubes when building mongrel engines, something I do quite a lot.
 

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Hi Jeff,
what is meant by 'B' Range?
"B" range = 650 and 750 twins, "C" range are the 350 and 500 unit twins. I don't know if there was ever an "A" range!
"A range" were the singles, although I don't know whether that referred just to the pre-WW2 singles or included the post-war Terrier and Tiger Cub. :unsure: Didn't include the '68-on BSA-based singles afaict.

As M'ick posted, "B range" were/are 650 and 750 twins, but that only applies to the units, also includes all the pre-units, certainly including the 500's, I think also 350's like the 3T and 3H.

Also as M'ick posted, "C range" are just 350 and 500 unit twins. One of the illustrated PRT in the John Healy guide is C-range, plus - certainly in the late 1960's and early 1970's - B- and C-ranges used the same PRT seals (allowing for 70-4752/3547), changed to the O-rings at the same time and needed the Service Bulletin 324 'fix' :ROFLMAO: at the same time.

"D range" was the triples.

the JRC guide set me on the right footing
(y) Regret I'm more-circumspect about the JRC guide (their alternators guide is riddled with detail errors :(). The TGB/PRT/seals guide contains at least one error/unexplained inconsistency - JRC reckons the 70-3547 seal is 3/16" thick, which would be thicker than 70-4752; I've never seen such an 70-3547, I've only ever seen 1/10" thick, those thinner 70-3547 having been a common fix for skimmed triple heads for decades.

Connected with seals, the JRC guide disagrees with the parts books in several years about seal part numbers, without JRC explaining why they disagree; absent easy access to original Triumph parts books update sheets, I don't know whether the parts books are wrong or JRC is mistaken about seal part numbers. :( It is significant and important when you're trying to assemble an engine with the white seals and get the correct "crush" ...

From what I have surmised, the PRT recess (1/32 in) in the head is identical for all late '62 through mid '68 heads, so I can use any of these date stamped years with the PRT (70-6000) that just came out of service, and ideally stay with the tappets, guide block and o-rings correct for my model year,
Essentially yes but be a little circumspect about any head with a cast "68" - as posted already, the '69 model year began in July 1968 ... if nothing else, measure the ID of what M'ick called 'the "socket" for the PRT'?

aftermarket alloy (vs chromed) alternatives are available, and though while lacking the rich finish of the chrome, would be corrosion resistant. I am wondering if people have had good luck with those?
If you wanted non-corroding PRT, keep an eye out on Fleabay for the stainless ones made many years ago by the guy who started Devon Rims? However, apart from you'd need a pre-'69 pair, I don't know how well they worked in practice (different expansion rate to cast iron or ally?).

I can see the point of ally ones on a triple, if the ally's the same as the cylinder block, so block and PRT expand at the same rate as the engine warms up, maintaining pressure on the seals. Otoh, and especially as ally PRT still corrode, I can't see the point of ally PRT on a twin, with a cast iron block? @DMadigan Dave makes adjustable ally PRT for triples, with a much better sealing system, I know he was thinking about making 'em for twins but I'm not sure if he went ahead? Hopefully he'll see the "Alert" and update us.

Hth.

Regards,
 
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