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Discussion Starter #1
Hello everybody :Wave

Right finger healed now from surgery, new copper head gasket and new set of PRT O rings and sealing ring delivered.

Now it's time to complete top engine re-assembly.

Everything went fine until I torqued cylinder head down and sealing rings protruded / bulged out and wedding band slid up.

I used P/N 70-4752 sealing ring 0.125 thou (3.2 mm) thick.
I noticed there is also a thinner ring P/N 70-4752T 0.099 thou (2.5 mm) thick available from LPW or P/N 70-3547 2.3 mm thick available from a French supplier.

Shall I use thinner sealing ring instead ?

Using a feeler gauge, I found a squish/gap of 0.07 thou (1.8 mm) between cylinder head joint surface and copper gasket installed on barrel with PRT standing on 0.125 thou sealing rubber.
Using thinner P/N 70-4752T 0.099 thou (2.5 mm) thick sealing ring, squish should be reduced to 0.044 thou (1.1 mm) which is more acceptable.

What do you think ?

Regarding cylinder head 3/8 and 5/16 studs, I noticed the thread at both ends of stud has a different length.
I fitted the longer threaded end downards on barrel and the shorter threaded end upwards to receive the cyl. head bolts.
I guess I'm right?

Thanks for your good advices.:wink2:
 

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Use the thinnest seal that will just squeeze down a tiny amount.Often,the gasket sets come with three thicknesses to pick from.In my case,it is always the thinnest one that fits.
I have also fitted a thick seal and had the ring ride up and it will not go back down again however much you try.
 

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Hi lilic24000, Hmm... Didn't we discus loose wedding bands??

Personally every band I've seen loose has come up sooner or later.

I was just setting PRT seal crush on the '69 Bonnie tonight. The wedding bands are loose on it. Got 2 new bands mail order, they were worse.

What I did was take a sharp center punch & made about 16 punch marks around the bottom of tube were band goes. This made band a tight fit. Cleaned very well. Roughened chrome just below center punches with some sand paper & roughened inside of bands. The put Loctite sleeve & bearing mount on PRT & band. Gently tapped band over PRT bottom with a small hammer. Left about 1/8" of band below surface of PRT bottom. Will let Loctite cure a good 24hrs. But The bands feel snug over the center punch marks.

On my desk is Triumph service bulletin #324. Regarding fitting of PRT & wedding bands. The spec for crush is .030-.040".

There is an error on the part #s for the white seals. They have it reversed. The correct #s are 70-3547 .100" thick. 70-4752 .125" thick. I have both #s in my hand & that's what they actually measure. From Raber's San Jose CA.

The info also states the "cadmium plated sleeve" (wedding band) should be a tight fit, but if not you need to secure with a proprietary bonding agent. They don't say what that agent is. I'm using the Loctite I mentioned above. Others have mentioned epoxy, that would work too. Tribond would work too, but let it dry at least 1 week before installing PRT or it can migrate.

I'd still do the "knurling" with a center punch. Do it lightly as not to out of round the tube.

Don't set band on cly. like shop manual says. That doesn't put band straight as block is canted in cly. Put band on PRT tapping in on gently with a small hammer. Work it down straight. Will not be hard to do since band is just being held by the center punch marks.

I tried to lay a bead of solder on the inside of band one time. Didn't work too well, it was too thick. I'd wipe it off, then too thin.

On my Tiger 750 I machined special stepped aluminum bands. Took all day. That was a real cure though.

Back to the crush of white seal. With the .125 I was about .045 gap. The .100 gives me a little over .030.

However as you may have found the front & rear tubes may crush different. Checking different heads, Triumph wasn't perfect boring them. On this head the exhaust side of head is about .010" deeper. So I decided to do an experiment.

I put on the thick seals with no bands & tightened head using center 4) 3/8 bolts. Just until they tightened just snug. I watched both white seals bulge out. They bulged way out. So far out if the band was in place they'd have hydrauliced & could have bent head.

Next I installed the .100 thick seals. Tightened head again. This time squish out looked good. Some bulge, but not much. Installing band & feeling it I could tell seal was just contacting band lightly & no danger of rubber hydralicing on band. Since head bores are not even, one is bulging more than the other, but that's ok since there is no binding. So the .100" is the seals for this head.

Looking at my notes from my Tiger 750 I had to surface head due to erosion from blown head gasket across front center bolts. In this case I used a .080" thick head gasket instead of normal .050" thick. That gave me only .015" crush. That was 7/7/14 & I've covered over 10k miles & it's still bone dry.

In some cases you may have to make a special thick white seal. Not easy, but if you have lathe you can put ring over a large socket. Spin it up & slice it with a razor blade. Takes a little practice, but you can do it.

You might take a bunch of flat washers, bolt & nut. Make a mandrel & put seal around flat washers & spin up in electric drill, then slice them.

Anyway get the wedding band secured tightly. What ever white seal you use make the bottom of band just slightly longer than height of the seal so band just covers seal.

On a side note, the white seal pushes up the PRT so the upper PRT seal makes contact with upper surface of head bore. I don't know how much that really helps the sealing, but it doesn't hurt it.

The service info also stresses the importance of deburring & smoothing bore of head & sides of tappet block so seal has a smoother surface to seal on. The stress importance of lube to help seals slide in smoothly. Triumph says oil or grease. John likes P-80 emulsion lube.

I've used oil & grease to good results too even though it may lead to leaks. So far it hasn't for me.

I've also used silicon sealant to good results. A very thin smear on top oring. Install immediately.

On tappet block that's risky or you can get silicon in oil drain holes. I only put on white seal. Then allow a tiny smear to be on side of tappet block just above the white seal. I put a very tiny bit of lube on lower round o-ring.

Lilic, What is your crush using an old flattened head gasket?

I'll post photos of the knurling I did with center punch tomorrow.

You got the studs correct. The long thread goes down into cyl.
Don
 

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Discussion Starter #5
Hi Don,

Thank you for your comprehensive response to my PRT sealing issue.

Hi lilic24000, Hmm... Didn't we discus loose wedding bands??
You're right but I just don't understand why PRT sealing was OK after first top end assembly and why it all of a sudden started to go wrong after succesive dismantling and re-assemblies.

Personally every band I've seen loose has come up sooner or later.
Original wedding bands were loose, like the replacement parts I've just ordered.

What I did was take a sharp center punch & made about 16 punch marks around the bottom of tube were band goes...... I'll post photos of the knurling I did with center punch tomorrow.
That would be helpful

The spec for crush is .030-.040".
OK Don, copied (that's also what Mr Pete recommended).


....the "cadmium plated sleeve" (wedding band) should be a tight fit, but if not you need to secure with a proprietary bonding agent. They don't say what that agent is. I'm using the Loctite I mentioned above...
Can you say Loctite reference number you use ?


Don't set band on cly. like shop manual says. .....Put band on PRT tapping in on gently with a small hammer. Work it down straight. Will not be hard to do since band is just being held by the center punch marks.
OK

...... So the .100" is the seals for this head
Will try this one.

...Anyway get the wedding band secured tightly. What ever white seal you use make the bottom of band just slightly longer than height of the seal so band just covers seal
Wilco


Lilic, What is your crush using an old flattened head gasket?
1.8 mm (0.07 thou) on inlet side and 1.6 mm (0.063 thou) on exhaust side

You got the studs correct. The long thread goes down into cyl.
Thanks Don
 

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Discussion Starter #7
Hi Don,

Don't bother with photo posting, take care of your Dad.
Hope he can feel better soon.

Fred
 

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Hi lilac, Thanks. Dad had bad stroke nothing we can do now but wait. Don't expect much recovery, has many other problems. Hope God calls him home soon.

The stuff I used for band glue is Loctite 640. Can fill up to .1mm gap. Good to 400f deg.

Remember when changing thickness of lower white seal the change in crush is not exact due to the tension lower seal applies to top o-ring. The top o-ring compresses more or less depending on the white seal thickness & the crush you have.

Look at photos & you can see light sanding on lower edge of tube to help glue hold & the small center punch marks.

Notice bad bulge with .125 seal. Then compare with good slight bulge with .100 seal. With some practice you can set head on PRT & fell the wobble of head & you can pretty much tell how it will crush. Takes some practice, but I bet you'll see what I mean with thin seals arrive.

See the white seal setting in the PRT wedding band? Notice how the band is out past the white. You want that, yet don't let band set on cyl. I needs some clearance.

Looking at band on fitted PRT you notice this '69 tube has a different profile than T140 but the concept is the same. Notice how far up it is on PRT. Trial fit before gluing. Get the band position where you want it. Remember it, then center punch & glue. If band won't hold for test, just start with 4 center punches.

Prior on your motor, my hunch is you had a lot of crush. I expect the upper o-ring was flattened a lot. I expect lower white was flattened at lot too. In the old days we just stuck them together. The risk is bending the head & head gasket leaks as the tube crush is so great it doesn't allow head gasket to pinch tight enough in center.

After getting band positon correct. Center punch. Wipe a smear of 604 onto tube & inside band. Set PRT on wood bench & gently tap band onto tube with a small hammer. Keep looking at band as you go to keep it straight. Not hard to do at all. Wipe off excess 604. Takes 604 24 hrs. to fully cure.

Here's the photos I hope they help you understand all this.
Don
 

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lilac, To be clear I leave the lower PRT round o-ring out during all this trial fitments. I will install lower round o-ring at final assembly.

If the lower ring is in during test fitting I find it just makes it harder to test crush as friction of that ring interferes with the test.

I find this method is very successful in having no leaks.

There is no doubt in my mind the band will stay put perfectly with the center punching & 604 retainer.

The bands in photos are the old ones. I just polished them. They will soon turn normal gray cadmium color once bike is on road. They were still in good shape with no rust whatsoever.
Don
 

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Discussion Starter #10 (Edited)
Thanks Don for the photos and further explanations.

I will try sealing PRT with thinner ring and Loctite 640.

Centre punches around PRT bottom to prevent wedding band from sliding up, right ?

Wish your Dad will be better in a while.
 

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Bonjour Fred, hi Don,

Everything went fine until I torqued cylinder head down and sealing rings protruded / bulged out
Can you say how much the "sealing rings protruded / bulged out" compared to Don's pictures, or post pictures of yours.

For what it is worth, on Don's pictures that he's marked, "Too much", I am saying, "Really? If that is causing the wedding band to slide up, the whole arrangement is far too much trouble compared to the way exactly the same sealing ring is used before 1969". :Darn

I noticed there is also a thinner ring P/N 70-4752T 0.099 thou (2.5 mm) thick available from LPW or P/N 70-3547 2.3 mm thick available from a French supplier.
These are the same ring; two pieces of rubber just 0.2 mm. different are not different parts. LPW sells mainly triple spares so the new owners have renumbered 70-3547 to "70-4752T" because, originally, all triples used 70-4752. It probably saves them having to explain to every new triple owner about different part numbers (70-4752 and 70-3547) for different thicknesses.

Shall I use thinner sealing ring instead ?
It depends. I explained in a previous thread how to measure and calculate what your engine actually needs. A small range cannot be specified for a seal that simply relies on a little pressure.

The seventy thou. - 0.070" or 1.8 mm. - would be too much but, as Don advised, you need to check without the lower O-ring inside the prt if that can affect the measurement. The 0.040" referred in the Service Bulletin is probably a good maximum but the 0.030" is a silly minimum; I have known half that to seal perfectly well.

loose wedding bands?
every band I've seen loose has come up sooner or later.
Could be because what you have marked as, "Too much bulge", is actually fine and would hold a wedding band in place?

What is your crush using an old flattened head gasket?
Uh-uh, Fred posted "new copper head gasket" in his first post.

cylinder head 3/8 and 5/16 studs, I noticed the thread at both ends of stud has a different length.
I fitted the longer threaded end downards on barrel and the shorter threaded end upwards to receive the cyl. head bolts.
More importantly, there should be a small raised 'pip' on one end of each stud; John Healy has posted before that the 'pip' stops the stud bottoming and sticking in the blind hole in the barrel, so it is those ends that should be in the barrel.

Hope this helps.

Amicalement, Regards,
 

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On my last outing,my prt seal seemed to have failed and a fair bit of oil leaked.Anyway,i cleaned the oil off and squirted some silicone rubber all around the join.Today out for a 40 mile ride and no leak yet.Just putting off the job until after Christmas.
Some years ago,i also bought new bands that were very loose and no use.
Looking at the bulge in Dons picture,i had one looking like that and it did push the wedding band up.I also glue that band to the prt but i have been using JB weld.
My last seal replacement was 3 years ago and it is annoying to fail this soon but will allow me to do a decoke.I might change the followers this time as they do have a little dip in the centre of the pad last time they were out.This dip does not cause any problems and has been like this for years but i just happen to have a few spare followers in the garage.
 

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Hi Guys, I don't know that an over squished seal is what raises band. I've seen them migrate up with perfect squish. Maybe its vibration??

The key factor is the band must be secured tightly to the PRT to keep it from moving. Whether by press fit or adhesives the band must be secured.

I find surface finish of head bore & tappet block seal surface is very critical in long term sealing as well as viton round rings. This cannot be over stated.

Regarding this arrangement, from what I observe on club rides, the wedding band type system does a better job of sealing long term that the earlier system. I might say way better.

One thing I'll give to BSA & Norton owners. They don't have to think about push rod tubes...
Don
 

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Discussion Starter #15
I leave the lower PRT round o-ring out during all this trial fitments. I will install lower round o-ring at final assembly.
If the lower ring is in during test fitting I find it just makes it harder to test crush as friction of that ring interferes with the test.
Don, are you refering to PRT bottom red O ring ?
 

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Discussion Starter #16
Hello Stuart :smile2:

It took me some time to read thoroughly and understand the lot of information gathered through all the posts.

Can you say how much the "sealing rings protruded / bulged out" compared to Don's pictures, or post pictures of yours.
Actually, my sealing ring protruding was worse than Don's picture.
Sorry, I didn't take photo of this "freak assembly":eek: and stripped everything down so as to avoid bending my poor cyl.head.

It depends. I explained in a previous thread how to measure and calculate what your engine actually needs.
Stuart, I kept good notice and record of your previous thread and method to calculate the crush.

you mentioned:

"There are two ways you could check the 'crush' on the white sealing rings:
. Fit the pushrod tubes and seals but without the pushrods.......
. Fit the pushrod tubes without the white sealing rings and without the pushrods...."

What do you mean exactly ?

1st method : I fit the PRT with the white sealing ring and no PRT top (black) and bottom (red) O rings ?

2nd method: I fit the PRT with no rings at all (no white, no red and no black O rings) ?


The seventy thou. - 0.070" or 1.8 mm. - would be too much but, as Don advised, you need to check without the lower O-ring inside the prt if that can affect the measurement....
You and Don are refering to PRT bottom red O ring, aren't you ?
 

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Discussion Starter #17
The key factor is the band must be secured tightly to the PRT to keep it from moving.
Whether by press fit or adhesives the band must be secured.
On the other hand, the fact that band slides up is a safe means to advise a poor mechanic that his squish is too much, hence preventing further damage to cyl. head.

I don't know how to reduce the squish apart from choosing thinner white sealing ring, or thicker copper head gasket (but this will decrease compression ratio), or like Code Man said , by just eliminating the white sealing ring and replacing it by a coat of silicone sealant.

Slicing up white sealing ring "custom made" using an electric drill (as per Don's previous post) is not in my skills:unsure
 

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Hi lilac, If you think leaving the wedding band loose is something you might do, you are mistaken. Don't do that.

The red round lower ring sounds like the one I like to leave off during measurements (the factory leaves it in, but I don't like to). The round profile rings can be supplied in different colors, but color doesn't assure what material ring is made of. The size of upper & lower round rings are the same. So just make sure they are viton whatever the color. If you only got 2 viton make sure they go on top of tube. Again I always use only viton round rings. I strongly recommend that. Hard to visually identify viton so you must trust what the seller says they are.

Again, don't forget to install lower round seal for final assembly.

To be perfectly clear the top tube o-ring & the square o-ring MUST be in place during measurements. The head gasket must be in place for measurements. I think you know that. You can install head nuts and/or bolts finger tight to hold head steady & level during measuring.

The Triumph spec .030-.040" is clearance between head & head gasket. This clearance gives the crush, meaning crush of the push rod tube seals once head bolts are tightened. However, we know from experience that .015-.040" will give good results. Having more that .040" gap can pose a risk of head damage. It depends on how much over .040" you go. After my head resurface I ended up with approximately .045" gap. Head did not bend, but at the time I didn't have the info to know better. I got lucky. One wedding band fit tight & stayed put. One band was loose & migrated up allowing white seal to bulge out & finally split. It caused minor leakage. As a stop gap measure, I stuffed a small black rag behind prt to absorb leakage.

You want to do better than I did back in the 70s.

When you get the thin square seals in you hands trial fit the push rod tubes & see what your clearance (gap) is.

The current part #s of the viton round O-rings is 71-1283V. To be used inside bottom of tube, & on top of tube. The square ring part #s you have. The .099 is same as .100 in real life.

This is not hard procedure to do. Stack feeler gauges together to make your measurements as needed. Stick some tooth picks or the like between head gasket & head to keep gasket down while using feeler gauges. I know the gasket can be wavy & can be hard to measure sometimes. Take your time & measure best you can. Adjust head bolts/nuts as needed to keep head level.

You are correct in thinking you need a thinner square seal or a thicker head gasket if you have more than .040" .

Leave push rods themselves out while making measurements. They don't have anything to do with the measurements. Leave rocker boxes off also.

When you get the new square seals trial fit the tubes & head. Then photo how you are doing gap measurements. If measurement is between .015 & .040" then tighten head nuts, bolts to snug & photo gap. I recommend leaving wedding band off for these trial fitments.

When all is good, then install/secure bands & do final assembly.

CodeMan's wedding band migrated up so he cut off white ring & siliconed wedding band in place. That is not recommended practice. He got lucky. You want to do it correctly.

Here's a link to Bulletin #324. It's the 4th post down. Open PDF link & print it.

http://www.triumphrat.net/classic-v...tips-for-getting-that-oil-tight-engine-2.html

You'll need to convert the part #s to the 1973 & newer number system.

So digest all this & get back to us after you trial fit thin white rings.

If you really need thinner rings, I'll make some & mail them to you.

You have all the info you need to get this right. You might spend all day trial fitting & measuring. That's ok. It's the final product that counts.
Don
 

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Discussion Starter #19
Thanks Don for taking time to give me detailed explanations and advices.

Will revert to you when I am through with gap measurement using thinner square white seals.
 

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Hi Fred, :)

previous thread and method to calculate the crush.

"There are two ways you could check the 'crush' on the white sealing rings:
. Fit the pushrod tubes and seals but without the pushrods.......
. Fit the pushrod tubes without the white sealing rings and without the pushrods...."

1st method : I fit the PRT with the white sealing ring and no PRT top (black) and bottom (red) O rings ?
Fit the PRT with the white sealing ring and upper O-rings, without the lower O-rings (because Don has posted these lower O-rings can interfere with a reliable measurement) or the head gasket. Hold the cylinder head in place above the block with, say, the four outer bolts tightened just finger-tight but squeezing the white sealing rings as little as possible. Measure the gap between cylinder head and block, subtract the thickness of the head gasket and you have how much the white sealing rings will be 'crushed' when the cylinder head is tightened against the head gasket and block.

2nd method: I fit the PRT with no rings at all (no white, no red and no black O rings) ?
Fit the PRT with only the upper O-rings. Fit the cylinder head on the block but this time with the head gasket between. Again, hold the head in place on the block with perhaps the four outer bolts but this time ensure tightening them does not leave any gaps anywhere between the cylinder head, gasket and block.

You should be able to raise each PRT a small amount, pressing the upper O-ring against the cylinder head; when you do this, measure the gap between the bottom of the PRT and the tappet guide block beneath it. This measurement would be the white sealing ring without any 'crush', subtract this measurement from the thickness of the white sealing rings you have (0.125" and 0.100"?) and you will know how much they will be 'crushed' when the cylinder head and PRT are refitted with the white sealing rings (and lower O-rings).

You and Don are refering to PRT bottom red O ring,
Yes, the one inside the bottom of the PRT.

By the way, as Don advised also, be careful referring to the upper and lower O-rings by colour. In '69 and early '70, one of the problems was both upper and lower O-rings were E7310 (70-7310); the material was red Buna-N, John Healy has posted this was not capable of enduring the cylinder head temperature at the tops of the PRT, particularly between the exhaust ports, it disintegrated and oil leaked out. :(

As is in Service Bulletin 324, Triumph respecified only upper O-rings to be black Viton - E11283 (71-1283).

However, both O-rings are the same diameter and thickness, so the better Meriden parts dealers supply the same Viton O-ring for both E7310 (70-7310) and E11283 (71-1283).

However, modern Viton O-rings are not always black ... :Not again

So colour is not something I would rely on, particularly from a 'full' or 'top end' gasket set that is advertised to cover several different years and there are many unused O-rings and other gaskets when you hope you have finished. For what it is worth, for something this important, I would always buy several Viton O-rings specifically and separately from a reliable Meriden Triumph specialist, always keep them separate from other O-rings in their own marked container and use them both top and bottom of the PRT.

I don't know how to reduce the squish apart from ...
:) There are two ways I can think of:-

1. Get rid of the wedding bands completely, use the method Triumph used on the twins before '69 and always used on all triples.

The wedding bands are supposed to stop the white sealing ring being squeezed from between the tappet guide block and the bottom of the PRT when the cylinder head is torqued down. On the triples and pre-'69 twins, Meriden put the white sealing ring in a "Bottom cup" (70-4746):-



... fitted over the tappet guide block before fitting the sealing ring. Also helping the sealing ring 'crush' if necessary, T160's had a thin fibre washer (71-1190) between the tappet guide block and the Bottom Cup.

If you use this method, you might need to replace 70-4752 (~0.125") white sealing rings with 70-3547/70-4752T (~0.100").

2. Use adjustable PRT. These are made in two parts, threaded together and with seals by standard off-the-shelf O-rings. They are made by an American - Dave Madigan - email [email protected]; Dave is well-known in the triple world for very high-quality parts.

Hope this helps.

Amicalement.
 
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