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Discussion Starter · #1 ·
Unit 650 - developed a pretty bad leak from the top-end recently. I've pulled the head, cleaned things up a bit, found a couple issues and now I'm looking for a little feedback before I replace what's needed and throw it back together.

I rebuilt the motor about 2 years ago (except for the head, which I shopped out) and have been beating it up as much as I can since. This leak kinda came out of nowhere, and even then it still ran well with no loss of power or compression that I could tell.

Here's what it looked like when I pulled it apart the other day:







While I was cleaning it up, I noticed a couple things, including the dimple on top of the right exhaust valve-stem. I'm guessing the adjustment was way too tight. I also noticed that the rocker spring on that side was completely collapsed, so that the rocker arm was floating freely on the shaft.





I don't see any cracks in the head and there was no sign of leaks around the push rod tube seals. It's a
66, so it's got the older style head/rocker box bolts that have to be torqued with the rocker boxes in place.
It almost looks like it was those inner bolts (that hold the back of the rocker boxes down) that may have been leaking, since I noticed some oil around those holes on the cylinder barrel and gasket, like oil leaked down from the head, through those bolt holes.

My plan was to run the head over some 800 grit on a piece of glass, replace the gasket, valve, and rocker arm spring... reassemble and see what happens.

My questions are:

#1, Am I missing anything?
#2, What would cause that spring to collapse in the first place? It looked fine when I did the initial rebuild.
#3, Do I need to think about replacing the valve guide? Didn't appear to be stuck.
#4, What can I do to prevent that same leak? Gasket-seal around the inner bolts? Replace with the newer style bolt/studs (i'm not convinced
that you can get a proper torque on the head with those older style bolts). I did use copper-coat when I built it the first time, and I followed the torque specs and pattern listed on the tri-cor rebuild sheet... I've read about annealing the copper gasket as well as some of the random home grown torquing rituals, but I feel like there is something else, specific to the older unit 650's that I'm missing.

Any tips or tricks are greatly appreciated!

Thanks
-BK
 

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No need to buy a new gasket, just anneal the old one.
You might want to check the flatness of the cylinder also, though it's usually the heads that warp.
Spring collapse? Hey, it's a fifty year old bike. You can replace the all the rocker shaft springs (a.k.a.: thackery washers) with shims and gain an extra one-eighth HP or so!

Basically, just do what the manual says, re-torque and check valves after running it the first time. Doesn't hurt to re-check the torque after the second or third ride either. Leave the top motor mounts off to make this easy.

Details: Make sure all threads are in good shape so you get the proper torque. Use the stock head bolt washers.

No magic really, just careful assembly and make sure everything is flat, and check that the pushrod tube 0-rings aren't too thick.
 

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we always do 3 re-torques on a new top end. and you need to up the torque up to about 35lbs on the 8 big bolts and 25 lbs on the center bolt.
Your pics show that it was leaking in at least 3 spots, surface the head with some 220 grit paper on a flat stone.
 

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I've found those thackery washers a bit fiddly and when checking them sometimes find the open end gets hooked up and is not left to rotate.

I like the idea of replacing themwith thrust washers.

Skim head, anneal gasket to make super soft, even torque down of the head, run up to operating temp' allow to cool right down, torque again.

This has worked for me, but would follow advice /\ /\ of those that do it day in, day out.
 

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Should check that all springs are applying same force, match your springs accordingly...check to be sure the length of the stem protruding out of head are the same length, and if not you should shim the springs accordingly....sometime the heads are reworked so much that the valves get buried deeper and deeper in the head.. ...valve with dimple is junk...triple check valve lash according to manual....when the valve is dimpled like that it is not allowed to rotate at its own will and will get worse in a hurry....also agree with advice above about flatness and torquing...
 

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I know you only rebuilt the bike a couple of years ago, but you might consider removing the jugs and check the state of the piston rings...there seems to be a lot of black on your pistons and head surfaces, also the valve guides may be worn...I can't tell if the soot is caused by oil or rich air/ fuel ratio. As far as the valve and rocker spring goes, you might want to check your oil feed and keep your adjustment within specs.
To prevent future leaks, Aneal the head gasket, retorque the head at least twice after the initial torquing; once after heating the engine fully and again after break in. Don't forget to check the valve lash afterward.
 

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Discussion Starter · #9 ·
Thanks for all the replies! All are helpful, and much appreciated.

I know you only rebuilt the bike a couple of years ago, but you might consider removing the jugs and check the state of the piston rings...there seems to be a lot of black on your pistons and head surfaces, also the valve guides may be worn...I can't tell if the soot is caused by oil or rich air/ fuel ratio. As far as the valve and rocker spring goes, you might want to check your oil feed and keep your adjustment within specs.
To prevent future leaks, Aneal the head gasket, retorque the head at least twice after the initial torquing; once after heating the engine fully and again after break in. Don't forget to check the valve lash afterward.
You know, the rings are something that have been in the back of my mind since I first noticed the problem. Also Part of the reason I wanted to get some additional feedback. I guess it's easier to do now, then have to do it again later, but in looking at the condition of the pistons and head, I didn't think there was anything too out of the ordinary in terms of carbon buildup... It's definitely possible that I was running too rich. I'm running a couple of re-sleeved monoblocs that I'm CONSTANTLY fiddling with. Anyone else have any thoughts about the rings being the culprit?

Did you ever re-torque the head bolts after the first real heating up of the engine after the rebuild and let's say after 250 or 500 miles ?
I re-torqued a couple of times after the rebuild. Can't say that it was exactly "on schedule" though. I would think that if it held for 2 years without incident, that I must have done something right. Kind of seems like it came out of nowhere. I suppose stranger things have happened though. At the end of the day, it leaked... so that means the seal wasn't tight enough.

When you say you shopped out your heads who did them I'm about to go through this on my bike 64 and face Ben looking around at shops and what springs to use. What did you go with
I sent the head to a local guy in Jersey. Fred at Bears Cycles in Neptune. I'm sure you can come up with someone a bit closer to you though. I'd throw up a post and ask some board members in MD. There are also plenty of folks on here that would be happy to have you throw it in a box, and send it over regardless of location. Wes at Four Aces... or even Tony who replied to this post.

we always do 3 re-torques on a new top end. and you need to up the torque up to about 35lbs on the 8 big bolts and 25 lbs on the center bolt.
Your pics show that it was leaking in at least 3 spots, surface the head with some 220 grit paper on a flat stone.
I always felt that the torque spec listed in the manual was too low, although I'm afraid that if I go higher, that I'd crush the rocker boxes or something! I have a tendency to go ape-shit when I tighten things... so on items like a head, where I'm still pretty new, I try to stick to the books. However, you sound pretty certain that it's worked for you. I'll try going a bit heavier, as well as anneal the gasket.

Should check that all springs are applying same force, match your springs accordingly...check to be sure the length of the stem protruding out of head are the same length, and if not you should shim the springs accordingly....sometime the heads are reworked so much that the valves get buried deeper and deeper in the head.. ...valve with dimple is junk...triple check valve lash according to manual....when the valve is dimpled like that it is not allowed to rotate at its own will and will get worse in a hurry....also agree with advice above about flatness and torquing...
My friend said the same thing about the valve spinning. makes sense. I was gonna replace that one valve and just lap it in. Never did that before... Anything I should look for when I pull it out, aside from a worn seat or guide?

-BK
 

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I always felt that the torque spec listed in the manual was too low, although I'm afraid that if I go higher, that I'd crush the rocker boxes or something! I have a tendency to go ape-shit when I tighten things... so on items like a head, where I'm still pretty new, I try to stick to the books. However, you sound pretty certain that it's worked for you. I'll try going a bit heavier, as well as anneal the gasket.


My take on head torquing,
I oversee 2 full time engine builders doing at least an engine rebuild a week and we use a higher grade of rocker box gaskets that have a metal reinforcing in them, and we do 3 full heat cycles on the engine head torques. that requires the engine to be started up (and guickly tuned in) brought up to 325 degrees head temp using a temp gun, then cooled over night and retorqued with a valve adjustment, this is done 3 times. usually on the 3rd time there is no change in anything.
when you look at the old films of the engines being assembled at the factory it shows guys using a "T" handle wrench tightening the head down. Now these guys were doing this all day long and had a real feel for it and didn't need a torque wrench, I also feel it is far more important to get the head bolts equally tight than it is to stick to a specific torque wrench reading.
Use copper coat on the gasket and just get all the 3/8" bolts as tight as you can comfortably get with a hand wrench, the important thing all the same tightness, be careful about overtightening the center bolt the can strip out rather easily.
once a head gasket leaks it normally cannot be sealed by re-tightening.
 

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Ensure all surfaces are flat.
Never mind the torque business, Triumph never did this - Tighten the bolts has tight as possible using a 6-7 inch wrench
Been doing this for the last 45+ without any problems.
The head gasket should be good quality .048" thickness, good idea to add a good quality non hardening head gasket sealant during assembly.
Fit new tracery washers every time.
Terry
 

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^^^^ ALL good solid advice...I know I will be re reading this thread when I pull my head (insert bad joke here)....
 

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Good advice by all here...I have fixed the dimples in the valves before by chucking them up in a lathe and correcting it. Then reusing them if they are in spec on the stem and the edge of the tulip is still fat. It is from having the adjustment a little tight. If you do replace the valve however, you should check the fit in the guide. A proper valve job includes reaming the guide to a specific size to "mate" with the stem. If it is too tight or too loose you can have problems. Also a brand new valve tulip is not going to fit in the seat like the old one did. Be careful as you lap and don't be afraid to send it out if you feel like yiou are over your head or cannot get a perfect seal.
 

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Discussion Starter · #17 ·
Good advice by all here...I have fixed the dimples in the valves before by chucking them up in a lathe and correcting it. Then reusing them if they are in spec on the stem and the edge of the tulip is still fat. It is from having the adjustment a little tight. If you do replace the valve however, you should check the fit in the guide. A proper valve job includes reaming the guide to a specific size to "mate" with the stem. If it is too tight or too loose you can have problems. Also a brand new valve tulip is not going to fit in the seat like the old one did. Be careful as you lap and don't be afraid to send it out if you feel like yiou are over your head or cannot get a perfect seal.
Thanks Wes, this is the kind of thing that I was nervous about. I kinda figured it'd wouldn't be as straight forward as just "popping in a new valve". I wish funds weren't so tight, or else I WOULD send it out. Figured it was as good a time as any to learn a new skill! Sounds like there's a slim chance that it'll fit correctly, and I'm just asking for trouble if I don't deal with the guide as well, no?

I'm not giving up just yet. I'm gonna go watch the "head chapter" of Hughies' video again, before I decide to start selling some of my stash. His vid and ALL of yours have been a HUGE help so far!

-BK
 

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we use hardened lash caps on many of the big cam race motors, they are just 5/16" hardened lash caps and are available at most every Ford dealership parts department. they are about $10 each.
 
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