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Hi Daryl,
lost as to how to improve this situation.
seems that there is only the top ring spacing the head from the PRT and then it's the PRT that's clearly holding the middle high.
'Fraid imho, at present, not at all "clear" the PRT are "holding the middle [of the head] high" - you haven't posted you've checked the flatness of the rocker-box gasket mating surfaces on the head? If the head has been "bent", they should show a similar discrepancy to the head gasket mating surface?

As you've found less than 2 thou. between the head's existing gasket surface and a straight-edge, imho the bigger gaps you're finding when the head's placed on the block point to some poor machining of the block's gasket surface? (n)

So before deciding whether "bending" or machining is the correct course, more clarification of what is "bent" or poorly-machined already?

PRT
no bottom cushion that I was expecting. What I have is exactly like the image in the repair manual at BB13.
feel like everything I've read implied a cushion at the bottom.
'69-on PRT O-ring seals are a vexatious subject,
look particularly on your bike at what's at the bottom of the PRT:-

. If you see a steel ring separate from each PRT, if they can be pushed up the PRT, you should see they hide an off-white or translucent seal between the bottom of the PRT and the tappet guide block.
... i.e. if your bike doesn't have "a steel ring separate from each PRT" nor "an off-white or translucent seal between the bottom of the PRT and the tappet guide block", imho don't fit them.

The problem with them is they can only be squeezed about 20~30 thou, but 70-3547 is ~100 thou. (1/10") thick, 70-4752 is ~125 thou. (1/8") thick :eek: and there never was that much of a gap on any twin without them - afaict, their fitting was some sort of bodge using seals dealers would have on the shelf already? (n)

bottom oring inside the PRT (that looks in good nick) and a top oring (between the head and the PRT top (that looks like it's completely had it. The exhaust one that I looked at is caked in oil and black bits).
Replace all four with new 71-1283 as mentioned earlier. Ime, don't faff around reusing something as cheap as an old O-ring, no matter how "in good nick" it "looks".

torque value for the head bolts?
(y) 18 lb.ft. The 25 lb.ft. in the workshop manual is a misprint. (n)

Hth.

Regards.
 

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Hi Daryl,

'Fraid imho, at present, not at all "clear" the PRT are "holding the middle [of the head] high" - you haven't posted you've checked the flatness of the rocker-box gasket mating surfaces on the head? If the head has been "bent", they should show a similar discrepancy to the head gasket mating surface?

As you've found less than 2 thou. between the head's existing gasket surface and a straight-edge, imho the bigger gaps you're finding when the head's placed on the block point to some poor machining of the block's gasket surface? (n)

So before deciding whether "bending" or machining is the correct course, more clarification of what is "bent" or poorly-machined already?



... i.e. if your bike doesn't have "a steel ring separate from each PRT" nor "an off-white or translucent seal between the bottom of the PRT and the tappet guide block", imho don't fit them.

The problem with them is they can only be squeezed about 20~30 thou, but 70-3547 is ~100 thou. (1/10") thick, 70-4752 is ~125 thou. (1/8") thick :eek: and there never was that much of a gap on any twin without them - afaict, their fitting was some sort of bodge using seals dealers would have on the shelf already? (n)


Replace all four with new 71-1283 as mentioned earlier. Ime, don't faff around reusing something as cheap as an old O-ring, no matter how "in good nick" it "looks".


(y) 18 lb.ft. The 25 lb.ft. in the workshop manual is a misprint. (n)

Hth.

Regards.
Hello Stuart, are you sure about no square-ish ring at the bottom of the pushrod tube? AFAIK if the bottom O ring is the internal type, there is nothing to push the top ring into contact with recess in the head. Once all of the burrs and such are cleaned up allowing the PRT to fit smoothly into the head, it's simple enough to measure the gap between the bottom of the PRT and the tappet block with the head lightly tightened down with the head gasket in place. Obviously, any head distortion and the like needs to be attended to.
Cheers (and a Happy New Year), Mick.
 

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Hi Mick,

Happy New Year to you too. :)

sure about no square-ish ring at the bottom of the pushrod tube? AFAIK if the bottom O ring is the internal type, there is nothing to push the top ring into contact with recess in the head.
Mmmm ... afaict (from the various reports of "It worked for me", "It didn't work for me"), the original O-rings-only design relied on precise machining of head, block, PRT and tappet guide blocks to compress the O-rings? If so, it was in practice that couldn't be achieved repeatedly, so one assembly of the same components was oil-tight, :) another seeped a bit (oh well, it's a Triumph), another leaked a lot ... :oops: Afaict from Darryl's posts, once he's replaced all the O-rings with the later Viton, he could find his bike's assembly of head, block, PRT and tappet guide blocks is oil-tight (insofar as as any Triumph PRT remains "oil tight" ...).

burrs and such are cleaned up allowing the PRT to fit smoothly into the head, it's simple enough to measure the gap between the bottom of the PRT and the tappet block
+1.

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Discussion Starter · #244 ·
I'm working out my head straightening plan. In the meantime, my tool arrived (thanks Dave) and the tappet blocks are out. Easy peasy. Point of interest, neither was installed perfectly square to the cylinders. Whatever I do, it will be an improvement.

I have also been pondering what to do about the seals and lack of cushions. I have found Service Bulletin 324. I read over on Britbikes a thread where a person was in a similar position and was puzzled how a cushion was added under the PRT, but no mention of how that affected the overall squish. He ended up using two head gaskets. Please check me on this, but I think if I add the cushion, I can use a thicker head gasket to balance it all out and end up, hopefully, with about .030 or less squish. Does that sound right? I'll have to measure the cushions to see what thickness they are and I believe the gasket possibilities are .025, .040, or .080. Also, do I NEED the wedding band or can I just put in the cushion?
 

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like you said - start by removing the right side outer cover - this will get you to the kick start mechanism and is a good place to start to find the problem - at this stage i would not remove the inner gearbox cover - taking the primary /left side cover off could be more informative
as a matter of interest -does the engine turn over ? -- remove the spark plugs engage a gear and wheel the bike forward if the engine is free and the clutch assy is OK it should turn the engine (squirt some oil into the bores first)
from the pics its looks to me that a lot of the chrome could be polished up to a reasonable condition
With all the parts there & a good parts book ,as long as the engine didn't throw a rod, you can get it running very good. Time & patience.
 

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Discussion Starter · #246 ·
I somehow missed Stuarts last input before my last post. :oops: Does SB 324 not apply? or it does and it's still not the best idea? Am i overthinking it? nothing new there.
 

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Hi Daryl,
pondering what to do about the seals and lack of cushions. I have found Service Bulletin 324. I read over on Britbikes a thread where a person was in a similar position and was puzzled how a cushion was added under the PRT, but no mention of how that affected the overall squish. He ended up using two head gaskets. Please check me on this, but I think if I add the cushion, I can use a thicker head gasket to balance it all out and end up, hopefully, with about .030 or less squish. Does that sound right?
No.

First thing you should understand about SB324 is it's the most horrendous pile of :poop: it's absolutely riddled with errors ... 😖 I strongly advise against taking anything in SB324 at face-value on its own.

Second thing you should understand about SB324 is it's well over fifty years old; in that time, many Triumph twin owners have found better ways of keeping their bikes oil-tight.

Third thing you should understand about SB324 is not all of its 'advice' has to be applied to every engine.

Fourth thing about SB324 is, despite it being so crap, note nowhere does it advise adding a second head gasket ... if nothing else, that screws up the rocker geometry ... Aside, it might be 'interesting' to read that BritBike thread, link?

Aiui your thread so far, the only evidence of PRT oil leaks is from the failed O-rings at the tops of the PRT? If so, why not just fit new updated 71-1283 O-rings:-

. One of the errors in SB324 is 71-1283 is shown fitted to the bottom of the PRT; :oops: some '70 twin parts books already show it correctly at the top of the PRT; what's missing from online parts books are the typed update sheets Meriden sometimes sent with new parts books but did send out periodically throughout any year.

. Previously-posted advice to fit 71-1283 O-rings both top and bottom of the PRT comes under, "Second thing you should understand about SB324 ...".

Absent any evidence of leaks from the bottoms of your bike's PRT, you might want to know/remember KISS ... :cool:

. Imho, don't fixate on adding "cushions" there - and then faffing about adding extra head gaskets - before you even know if there'll be any problem with the new 71-1283 O-rings top and bottom of the PRT?

gasket possibilities are .025, .040, or .080
I'll have to measure the cushions to see what thickness they are
. Why not just use one of the fitted head gasket thicknesses to ensure the 71-1283 O-rings are pressed correctly so they seal ... but the head isn't bent when torqueing ...? :cool:

. If you fit "cushions", they need the 71-1707 "wedding band" or the pressure on the "cushions" from torqueing the head squeezes them out from under the PRT ... and then there's a leak ... :oops:

. Then each "wedding band" must be a close-but-sliding fit over the corresponding PRT ... or it cannot retain the "cushion", and the "cushion" expanding outwards when the head is torqued cannot retain the "wedding band" in position ...

In case you were wondering, I too have a strong suspicion Heath Robinson and Rube Goldberg helped design this 'fix fix' ...

Hth.

Regards,
 

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Discussion Starter · #249 ·
Thanks Stuart. I needed to take a breath. You are correct, if there wasn't an oil leak (a new one), I wouldn't have taken it apart and I only took it apart to replace the 3 orings, 2 on the prts and the 1 on the tappet block. The thing that got me wound up was the evidence of exhaust escaping past the head gasket.

Apologies for the incorrect Britbike reference, I couldn't find it there either. ;) The thread was on this site. Need Help with Tappet Block and PRT I did read a few on Britbike and got confused.

Thanks for providing a more direct assessment of the service bulletin in question. I feel like I keep giving too much credit to the factory despite quite a lot of evidence that they didn't get everything right. :unsure:

I'm going to have a conservative go at flattening the bowed head. Then a slow march to reassembly, keeping an eye on the clearances.
'
 

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Hi Daryl,
Apologies for the incorrect Britbike reference,
No worries, I know there are a few similar threads there ... I can remember one where the OP ended up cutting 70-3547 or 70-4752 seals in half to fill the gap that was at the bottom of his engine's PRT but not leave a huge gap between block and head ... :eek:

Mmmm ... bear in mind too that's about a later 750 twin - Meriden shortened the 750 engine height by shortening the cylinder block (by one fin), I think they don't have the potential option of not fitting a 70-3547 or 70-4752 seal and 71-1707 "wedding band" at all?

To be clear, unfortunately I can't be absolutely 100% certain your engine's PRT won't leak without "cushions" and "wedding bands"; :( what I'm going on are: some '69-on twin owners have posted in the past that their bikes didn't leak from the PRT; (y) you posting you didn't find any evidence of leaks from the bottom of the PRT; (y) @Mick Barratt posting checks you can make when you assemble the engine. Otoh, as you've discovered from reading, adding the "cushions" opens a can of worms; if it isn't necessary ... (y)

Hth.

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Discussion Starter · #251 ·
I have a question about the tappet block seals. The ones I took out were hard and brittle, as expected. What I wasn't expecting was that they were both not only in the groove but also smashed between the block and the cylinder piece. Is that the norm? I don't think it would have affected the sealing ability, but it would have raised the install height slightly.
 

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That's certainly not right, but probably not unusual, I "ease" the sharp edge of the barrel hole to help the O ring go in, I don't use sealant, just a bit of grease. Of course, getting the correct O rings is essential.
 

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I somehow missed Stuarts last input before my last post. :oops: Does SB 324 not apply? or it does and it's still not the best idea? Am i overthinking it? nothing new there.
For what its worth, here is my experience with sealing the push-rod tubes.

Soon after I got my '72 T100R, I started to get quite a bad oil leak from both push-rod tubes. I found that both wedding bands had slipped upwards and the square section o-ring located under the push-rod tubes had partially slipped out and allowed the PRT's to drop down enough to cause leaks at the top o-rings. I tried very hard to push the square section rings back into place to allow me slide the wedding bands back down again, but to no avail. I lived with the problem for many months with a cable-tie around each square section ring trying to keep them in place, but it only partially worked until I removed the cylinder head to do some other work.

I found the push-rod tubes (70-9512*) were both serviceable and to avoid a re-occurrence of the "wedding-bands" slipping up and allowing the bottom o-rings to be displaced out, I decided to carry out the remedy and procedure laid out by Service Bulletin 324. The bands were secured with Loctite 640 to the bottom sleeves of the push rod tubes as an option recommended in the bulletin. They are now permanently fixed in place. This worked extremely well and no further leakage has occurred over 10000 miles since.

* These are the earlier '69-'71 type rather than the '72-'73 (71-2576) push rod tubes, that according to the parts manual, would possibly have been originally fitted to my bike at the factory. The earlier ones are preferable if using the permanent mounting solution, as they have a wider sleeve at the bottom, giving a greater area to secure the "wedding bands".

There are some errors in the bulletin, with regard to the o-ring part numbers being reversed, but I found the procedure worked very well for me
 

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There are some errors in the bulletin, with regard to the o-ring part numbers being reversed, but I found the procedure worked very well for me
As with MANY recommendations, tips, and bulletins, "your mileage may vary".

Some report success, some report failure, some report partial success/failure.

Such is this crazy world...
 

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Discussion Starter · #255 ·
I thought I replied, but I guess I typed it and never posted it. :rolleyes:

The gist of the message was that I'm going to have a conservative go at leveling out the head/cylinder so there's less of a gap. And then a slow conscious reassembly keeping an eye on the clearances.
 

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Discussion Starter · #256 ·
Minor update. I have improved the head/cylinder clearance. I was well down the road of copying the press technique and then altered course. I read a post by John Healy and that then got me to several videos of warped OHC heads being repaired. It is critical on an OHC head to get it level because the cam is involved. They can't skim the head only as they would end up having a camshaft path that was a bump instead of a line. The way they do it is by shimming the outer end of the head, installing only the center head bolts (to either a flat block or a flat steel plate), and then putting the assembly into the oven. So that's what I did, shim the end and then clamp it using only the 4 center bolts. I torqued it to 18 ftlbs. I ended up doing it twice. The first time I went to 275F and the second to 300F. I wasn't comfortable beyond that. The net result was a gap of .0025" on the ex side and .002" on the intake side measured through the middle at the PRT gap. Previously it was .0055" and .0035".

The second item is that I VERY dry fit the PRTs. At the bottom, the PRTs on my bike sit on the tappet blocks. I put them on and they do, indeed, sit on the blocks. The tops are castellated. The tops on mine get an outer o-ring that is the squish for this setup. Interestingly, without that o-ring, the castellated part hits the head. The top end of the machined bore for the PRT ends before the PRT completely hits at the o-ring ring. I hope that makes sense. You can't put the PRT up in there and spin it as it's cocked from interference at the top. I'm not sure if you can make it out in the picture. Light Motor vehicle Automotive tire Bicycle part Gas

I'm going to grind a bit more clearance in there. That's the exhaust side (leaky side) btw. I don't know for sure if the oring would keep that away from the metal, but better safe than sorry. The other side seems to just have less meat on it and so does not interfere.
 

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Hi Daryl,
At the bottom, the PRTs on my bike sit on the tappet blocks
Does the PRT hold/trap the bottom O-ring? The PRT doesn't just squeeze the O-ring between it and the tappet guide block?

I'm going to grind a bit more clearance in there
better safe than sorry.
Mmmm ... bear in mind it's easier and cheaper to remove metal, it's harder, expensive and time-consuming to add it back ...

If you haven't already, would reading Vintage Bike Magazine » Push Rod Tubes clarify or confuse? It's hard going because it's aimed at 650 and 750 twin owners, it isn't always clear which bits also apply to 500's. :( In this case:-

Yellow Sports gear Personal protective equipment Service Machine


Late 650-750 twin head used 1969-1982
The recess in the head for the “O” ring is 1.140″. There is a small step with a small radius to align the “O” ring. The o.d. of the “O” ring when mounted on the tube is 1.200″.
Cylinder Nickel Auto part Engineering Household hardware


650-750 twin tappet guide blocks

Above:
Left block (70-1477) the shoulder is: 0.125″ 1/4″
Middle block the shoulder is: 0.1875″ 3/16″
Right block the shoulder is: 0.1875″ 3/16″
The outer diameter is: 0.9995″ to 1.000″
The hole in the cylinder should be: 0.999″
The angle of the hole is: 3.3°
... also applies to the 500 head and tappet guide blocks; "Right block" is E9352/70-9352 your bike should have.

The sketch of the various PRT is also biased towards 650 twins:-

. How does the length of "71-2576" compare to your bike's PRT?

. Aside, aiui the second line of the "70-9349" caption also applies to 500 PRT except it'd read, "70-9512 was fabricated 71-2576 was one piece". Afaik, only the "one piece" PRT are available new today (for both 500 and 650) but, helpfully, many modern retailers sell them under the "fabricated" part numbers ... :rolleyes:

Because of the above and:-

At the bottom, the PRTs on my bike sit on the tappet blocks
... I wonder whether new PRT might be an option? Reason I wonder is:-



... and the image in Klempf's British Parts. TUBE, PUSHROD, 500, 1969-74 appear to show the updated PRT fit over the tappet guide blocks to trap the standard O-ring? Is it worth having a chat to a long-time dealer like Mitch?

I'm sooo glad, nearly forty years ago when my T100 was being assembled, I asked Mate O'Mine to fit '67/'68 cylinder head, PRT, TGB and seals ... :rolleyes:

Hth.

Regards,
 

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Discussion Starter · #258 ·
Thanks Stuart. I have read that vintage bike article. Translating from 650/750 to 500 was beyond my present ability. Thanks for interpreting the relevant bits. It initially seemed helpful until I tried to understand how it related to my specific case. Then I thought it was just confusing me. I'll measure the PRT length and compare.

Also, I plan to clean up the old orings to see what's really going on with the ring taking up it's space. I'm not sure if I understand your question re holding/trapping the lower o-ring. The o-ring goes in a groove in the PRT and then is sandwiched horizontally between the PRT and the block when assembled. I think fitting the old o-rings will tell me whether the PRT still bottoms out or not. Is that what you were asking?

The CBS PRT looks identical at the bottom to mine. The only difference, at first glance, is the castellated part at the top on mine is enclosed on the new one.
 

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Hi Daryl,
question re holding/trapping the lower o-ring. The o-ring goes in a groove in the PRT and then is sandwiched horizontally between the PRT and the block when assembled.
(y) Thanks for clarifyng, I wasn't clear after reading:-
At the bottom, the PRTs on my bike sit on the tappet blocks
The CBS PRT looks identical at the bottom to mine. The only difference, at first glance, is the castellated part at the top on mine is enclosed on the new one.
There are at least 3 different types - smooth top, drilled top, and castellated.
Aiui, "smooth top" is pre-'69, "castellated" is '69-on what the Vintage Bike article calls "fabricated" (500 70-9512, 650 70-9349, "drilled top" are what the Vintage Bike article calls "one piece" (500 71-2576, 650 71-2575) that can be retro-fitted to '69-on?

"smooth top" pre-'69 doesn't protrude through the head, they're sandwiched between 70-3547 and/or 70-4752 top-'n'-bottom in the head and on the tappet guide block.

'69-on protrude through the cylinder head into the rocker-box:-
... shows the "castellations" locate the top of the PRT in the head, the low points between the "castellations" allow oil draining from the rocker-box down the PRT? The superseding "drilled top" similarly locates the top of the PRT in the head, the holes similarly allow the oil draining?

Hth.

Regards,
 
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