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Discussion Starter #1
I just want to double check about where to measure the correct crush distance for the pushrod tubes and to know if .025 to .030 spacing sounds right to you guys. I watched a guy on YouTube (https://www.youtube.com/watch?v=gVPXdNc-tls) measure the space there but would like to know what you think about his technique?

What I did was temporarily install the head with the head gasket on the cylinder and the pushrod tubes "without" the o-rings but with the white base ring under the tubes and measured the free play of the tube between the base ring and the cylinder head. Please see my photo below and let me know if this is the right way to do it? Just to let you know, I did not tighten the head down. It's just resting on the head gasket. As it sits now it reads just a little over .025 (.025 is as high as my feeler gage goes but think it's not more than .030).
 

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Hi Gary, Looks like you are making some good progress. I looked over my journal & here's what ended up with. 1st though, remember I had .010" skimmed from the head. You head is skimmed also, but by how much overall?
I'm going to repeat my self, but be sure to use the .080" head gasket. You must keep the compression as low as possible. Also take some fine emery & polish the bore in head & exterior of tappet block so O-rings will have a nice smooth surface to seat against. The head often has a sharp burr on the bore & I will scar the seal so make sure it's smooth so the seal will compress into head smoothly.
Also make sure you use Viton O-rings where the 4 back ones are & I'd use the thick stock white one down low.
Also the wedding bands should be light press fit on the tubes. Some T140 motors have undersized tubes at the bottom & the band can slip up & not contain the white seal. One of mine was like that & would migrate up cockeyed. I made a home made band, or would have had to get a new proper sized tube. Some lay the band on the bottom, some tap the band slightly onto the tube. I used to always lay the band in 1st, but this time tapped it onto the tube. Just a few thou on so it holds on tube. I liked tapping on tube better I think.
There are various ways to check seal crush. I don't know if the way the video shows is best are not. I don't subscribe to it because it doesn't take into account the o-ring cross section. I may be wrong, but that's my feeling.
I got a bunch of square rings from Raber's to experiment with so I'd have a selection.
I put all 3 O-rings on both tubes but no wedding band. Set head gasket on & used a few head bolts finger tightened lightly to hold head level, but not compress seals.
Then used feeler gauge between head gasket & head. My tubes were different lengths & for whatever reason the head sits leveler with what was inlet tube on exhaust side, so check both ways for best fit.
I got 015". I was wanting about .030. The next thicker square seal was way too thick. So I settled for .015" after much fiddling with cutting the thick seals on the lathe with a razor blade. I gave up on .030 & went with .015.
I put a thin smear of silicon on all 3 seals. I don't let it dry, installed head right away. I also smeared a light coat of Mercedes Benz # 002989472010 sealant on both sides of head gasket. I used black Mercedes Silicon, but other silicon works well also. As would Honda or Yamaha bond silicon.
Torqued head to specs from manual. I've had no leaks at all, I mean bone dry.
Be sure to knock the burr off head gasket as I will have a sharp side. We want nothing to create a hot spot that might cause ping.
Long ago... my head gasket blew to center bolt & eroded head so I had to skim it. I didn't think about seal crush back then. Just installed with all new seals & .050" gasket.
When I had apart last summer to do tappet block seals I check head for flatness & it's still quite good. I can't get a .0005 blade under straight edge. I covered a good 6k miles with that set up & no head bending.
Don
 

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The top O-ring will be 0.100" cross section. If you try to squeeze that into a 0.030" gap, you'll have 0.070" crush.
Crush is the total amount that the O-ring and lower seal need to compress, when the head is torqued.
 

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Discussion Starter #4
TR7RVMan

Hi Don,
I'm not sure how much has been skimmed off the head. I bought the head on ebay and not sure if it had been skimmed by previous owner/owners. After I obtained the head and took it to a local machine shop for them to do a valve job they told me that they took not more than .005 off of it. I took your earlier advice and bought a thick .080 copper head gasket and that's what I had on the engine when I measured the spacing of the tube and the white base ring.

I'm confused about how many seals you're talking about:

Also make sure you use Viton O-rings where the 4 back ones are & I'd use the thick stock white one down low.
Only three o-rings came in the rebuild gasket set: One thick white seal that the PRT rests on, one black o-ring designated specifically for the top of the PRT and one other black o-ring that fits inside the bottom of the PRT. Also, when talking about the "wedding band" are you talking about the metal band located at the bottom around the white seal?

Both intake and exhaust PRT's look the same and I only measured the front exhaust PRT spacing and didn't think that there would be a difference in spacing between the intake and exhaust tubes. I'll have be sure and check both.

Gary
 

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Firstly, I`m not impressed with that video.
What I saw of it.
You need the top O-ring on the tube.
Make sure the tubes are pushed into the head with the rings.
With the head + tubes resting on the lower white rings, level the head.
Then measure the gap between the head and gasket.
I go for about 0.040"
25 + 15 thou feelers.
 

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Like Caulky says is the best way (the only sensible way). Like Pete says, what you're interested in is the amount by which the O rings will get crushed when the head is tightened down. You can measure that using feeler gauges between the head & barrel (with the gasket you're using in place). That figure is the amount the head will move down when tightened. It mustn't be too much or the head will try to bend itself as the PRTs resist movement. And it mustn't be too little or the O rings won't do their job.
 

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Discussion Starter #7
Firstly, I`m not impressed with that video.
What I saw of it.
You need the top O-ring on the tube.
Make sure the tubes are pushed into the head with the rings.
With the head + tubes resting on the lower white rings, level the head.
Then measure the gap between the head and gasket.
I go for about 0.040"
25 + 15 thou feelers.
Hello Caulky,
Thanks for your input. When doing what you said above, should the bottom o-ring be inside the PRT or just the top o-ring be installed?

Gary
 

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Hi Gary, Sorry for the confusion. I should have stated that differently. Back should have been black. Meaning 2 black o-rings on each tube. You are correct on your ring positions. As you think the wedding band is the tin ring that goes at the bottom.
Even though the black rings are the same size originally only the top was Viton, now both should be Viton as it resists heat better to reduce leakage.
What is your gap between head gasket & head?
Don
 

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Discussion Starter #9
What is your gap between head gasket & head?
Hi Don,
I haven't had a chance to work on the bike in the last couple of days but will put some time in tomorrow. I'll let you know how much space I have at the head gasket then.
 

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Discussion Starter #10
Hi Gary, Sorry for the confusion. I should have stated that differently. Back should have been black. Meaning 2 black o-rings on each tube. You are correct on your ring positions. As you think the wedding band is the tin ring that goes at the bottom.
Even though the black rings are the same size originally only the top was Viton, now both should be Viton as it resists heat better to reduce leakage.
What is your gap between head gasket & head?
Don
Don, Caulky, Mr Pete, John A,
I did what Caulky suggested and with the top o-ring installed on the PRT's and the PRT's installed in the head and well seated into the head, I installed the head without the lower o-ring inside the PRT's but with the white band under the tubes and measured the distance between head and head gasket. It measured about .069 and the only thing holding the head off the head gasket was that the PRT's were resting on the white square o-ring. So, what I'm worried about is the white o-ring(about .125 thick) under the PRT's will not crush .069 inches without warping the head again. So, what thickness do you think the white square o-ring should be?--.060, .065, .070??:confused:

Thanks for your input,
Gary
 

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Hi Gary, Hmmm that's a tough one. Since the thinner the white is the less it will crush I'd go about .060-.070 thick of white seal. Rabers sells these seals in .125 & .100 thick. You'll have to cut one in 1/2. I have 2) .040" thick sections left over from some I cut when I was doing experiments on my motor. Those are probably too thin.
Now I'm wondering how much was really taken off your head. That could really raise compression.
Hear's a question, what happens when you use no lower ring at all, does the push rod tube still have up/down play? At all costs we don't want it to bottom on the tappet block.
You could try cutting a white ring by putting in on a 1 1/8" metal rod in lathe & slice it using a new razor blade. I've done that a few times & it's easy to cut but the thickness can be a little of a crap shoot as the rubber wants to migrate so to cut one dead center is not easy.
If you can't find someone with a lathe, mail the rings to me & I'll give it a shot at cutting them thinner. If you sent several I could cut some different & you'd end up with an assortment.
In a pinch you could always put a round o-ring from hardware store on the very bottom. If silicone sealant is used it would not leak. A 1" id x 1 1/8od 1/16wall is a size that hardware stores usually carry.
Again, in any case, try the tube without the white oring, but top ring in & see what play you have just to be sure you have some play.
Regarding head thickness from new, that I had a hard time figuring...
I don't know how thick a new head is, or what the production variance is on new head thickness. I measured my head. Set head on drill press table & used a depth gage down head bolt holes. My head is slightly tapered left to right. but both top & bottom gasket surfaces are very flat. One side was 2.775" the other was 2.785". I suppose the machine shop that surfaced my head made it a little crooked, but with push rods it doesn't matter, if it was chain drive overhead cam, would be a problem.
If you want me to cut some white rings for you let me know. Call me. I have your phone # in case you didn't get mine.
Don
 

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Regarding head thickness from new, that I had a hard time figuring...
I don't know how thick a new head is, or what the production variance is on new head thickness. I measured my head. Set head on drill press table & used a depth gage down head bolt holes. My head is slightly tapered left to right. but both top & bottom gasket surfaces are very flat. One side was 2.775" the other was 2.785". I suppose the machine shop that surfaced my head made it a little crooked, but with push rods it doesn't matter, if it was chain drive overhead cam, would be a problem.
If you want me to cut some white rings for you let me know. Call me. I have your phone # in case you didn't get mine.
Don

The head won't be measured in "thickness. That will vary from head to head. Even brand spanking new.

It will be measured in the min. / max CC's of the combustion chambers.

This is measured with liquid, and a burette. Hopefully someone here knows the numbers because I am curious myself.

Here is the method...

https://www.youtube.com/watch?v=V7V40ZWNgCo
 

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Discussion Starter #14
Caulky

Buy a thick head gasket.
These are .080" thick, the normal ones are about 40-50 thou thick.

70.4547/80 HEAD GASKET 9 STUD 650cc SOLID COPPER (.080") THICK £12.50

http://www.tms-motorcycles.co.uk/store/products/list.asp?cat_id=115

You may be able to buy these locally?
Hi Caulky, thanks for your reply, I measured it with a new .080 thick copper head gasket. Maybe I'll need to put a thick gasket under the barrels? Also, FYI this is a 76 T140V engine going in my 70 T120R frame.

Gary
 

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TR7RVMan

Hi Don,
Thanks for your offer on cutting my o-rings and I'll probably take you up on it and mail you the o-rings but first I'm going to call Rabers tomorrow when they're open and see what kind of o-ring thicknesses they have. I'm going to need those Viton O-rings you were talking about for the inside of the bottom of the PRT's so might as well see what they have regarding the white o-rings. I just went down and measured the space at the bottom of the PRT's without the white o-ring and it measures about .070 and the head is sitting flat on the head gasket. I snapped a picture attached below.
So when we talk about the "crush", we're talking about the "White square o-ring" that the tubes rest on and it should crush about 30 thousands - right? Or, is that top o-ring suppose to be part of that .030 crush?

Gary
 

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John, thanks for the info. Gary, maybe pick up about 6) more 70-4752 white rings like you have .125". Just in case one or two gets spoiled (it happens), get 4) 70-3547 thin
.100" rings. The .100 rings from Raber's will be clearish, not white. That's what I got from them anyway. They are closed Sun. & Mon.
Mail me the white rings & I'll cut them various thickness'. Then you can put them on & put feeler gauge at head gasket again. That way you can't loose.
The Viton PRT seals from Rabers are #71-1283. Again get extras.
The base gasket I used is 70-6903 the normal very thin one. They sell a thick one. I looked at it & it's made like the alum. reinforced rocker box gaskets. Need to be very careful to tighten evenly as not to cock cly. with the thick one. It scared me. I don't know if it's made, but I'd feel better with 2 thin gaskets & a steel shim, or even just a steel shim & no gasket. Use the Mercedes sealant on it.
Raber's rocker box gaskets #712599E (the E is important) work very good!!
Their rocker cover & primary cover gaskets work quite well also. I recommend get several so you have spares. 6 hole V/c gskt #71-3673. Primary 71-7009. You'll have to trim the inner rear of primary gasket or it'll rub chain. But I've had no leaks with this gasket.
Don
 

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Those are our CovSeal gaskets.
They are a very thin sheet of stainless steel with rubberized gasket material bonded to both sides. We have them for the base, rocker box back through the non-unit models and 500, 6 hole T140 rocker cover and TR6 inlet manifolds. They work very well on the rocker boxes, but would only advise using them on the base where there is no step between crankcase halves (usually seen on 1971 and up models).

We also supply a double thick primary for he 650-750 twins.
John
 

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Discussion Starter #20
Order all the extra o-rings and the special rocker box gaskets from Raber's. To make the shipment worthwhile I also ordered new exhaust pipe to head clips and they had to special order those clips because I wanted UNF threads in them so it'll probably be the end of next week before I can continue with any updates to this forum thread.

TR7RVMan,
I'll send you the o-rings as soon as they arrive. Good talking to you on the phone and thanks for all your help.
 
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