Triumphrat

josh

Well a couple months ago I had an issue with my newly rebuilt top end: http://www.triumphrat.net/classic-vi...ml#post1277076

That issue turned out to be caused by a loose fitting exhaust valve guide on the left side, which the valve eventually got stuck in and then made some light contact with the piston. I had the head rebuilt by an experienced Triumph mechanic and got the engine back in the bike, lots of time and $ (and checked the clearance btwn valves and pistons - it was fine).

Anyway, she started up and I was running it lightly around the neighborhood to get the timing and carb settings right. I initially had the timing too advanced because it was backfiring at idle and kicking back, but really ran great at mid rpms. I probably rode for 5 miles this way, real light running under 30 mph. It was having an issue where it would sputter and die after about 15 minutes, I thought it was a battery/charging issue, but it may have been a heating up issue...Then yesterday I finally had the timing right where it was starting/idling really nice and all of a sudden, it starts popping out of the right exhaust pipe and running like crap, then running OK, then making a lot of valve noise so I shut it down. I decided to take the valve inspection caps off and noticed a ridiculous amount of tappet clearance on the right cyl exhaust. Not good. I took off the exhaust and saw a gap between the valve and the head. Not good. So off it all came and this is what I found:

Note the light coming thru the valve on the lower right. The exhaust valves are clean - must have been getting hot. There is also a TON of soot in the head after the exhaust valves and into the pipes.


All of this oil wiped right off with a clean rag - piston tops and cyl bores look great, no evidence of contact with valves.


brass gooed up on my valve stem

So I guess my question is - can running the ignition overly advanced lead to overheating that would cause a stuck valve? What about running rich...normally you'd expect cooler operation running rich...? Or do I have an oiling problem? I know oil is at least going to the rockers because the feedpipes leaked when I started it the first time, and the head had plenty of oil drip out when I was disassembling. The first go round I had the Left exh valve seize - this time it's on the right? I'm at a loss for words. The oil pressure indicator was sticking way out of the timing cover when running, and I had return oil pumping to the tank. The other three valves operate smoothly in the guides and have minimal wear. I believe the tappet clearances were correct as I had checked them each day before I ran the bike (.010" for '55 Thunderbird).

Anyone have any thoughts? I'm frustrated with this machine!

Josh

pookybear

Josh,

Only two thing do come to mind. An overheated engine could end up
galling up a valve stem. That is the first, second is where the guide
sized when they were installed. They may have been too tight to
start with. My later manual (1979) states a .002" of clearance. But
your manual may state something

Pookybear

josh

One other thing - the exhaust pipes turned blue near the head shortly after I started it up the first time, before I changed any carb settings. I think that's a sign of overheating too.

I'm not sure what the clearance was or what it is supposed to be between the valve and guide. Manual states nothing and the head came back fully assembled...

pookybear

Josh,

Ah you have to read between the lines sometimes to get the
answer. Look in your manual. It will give you the bore diameter
of the valve guide. It will also give you the valve stem diameter.
You take the maxium stem diameter and subtrace that from the
minium bore diameter to get the minium clearance for the guides.

Blue pipes is a lean condition that causes a slightly hotter running
engine. A little blueing can be normal, but only for a few inches
of pipe length. However, timing can also affect this as well, being
to retarded at higher rpms will have the fuel still being burned when
the exhaust valve opens.

Pookybear

RetroRod

Josh,

There will no doubt be better informed opinions than mine, but for what its worth, this is my view.

1. Advanced timing will certainly contribute to an overheated engine, however the heat will be concentrated on the chamber and the exhaust valve will be closed.

2. Retarded spark will also cause overheating of the headers as the combustion gases are still active when the exhaust valve opens, thus heat is concentrated around the exhaust valve port and the tops of the header and bluing occurs.

3. Lean, not rich, mixture contributes to overheating. Therefore, if lean and retarded, the exhaust port is going to get v. hot. If lean and advanced, the chamber will get very hot, and could lead to holed pistons.

Notwithstanding the tuning issues, I'm inclined to follow Pooky's reasoning of the exhaust valve not operating properly. There are many things that could cause this. Too tight in the guide, bent from a past experience, not lubricated, heat induced seizure. Others may have other experiences to relate.

Seems you'll need to ream that guide at the very least, check the valve stem and pushrod for straightness, and reassemble. Just make sure the ignition timing is just right, and the carbies are set as per the manual.

Hope this helps you a bit. RR

josh

Retro and Pooky, I appreciate both your comments!

I have double checked the manual, all she states regarding the valve guides is literally "tap them out with a drift, then tap new ones in", doesn't even mention heating the head first. This is a Floyd Clymer manual reprint, although I may be missing the info as I have experienced finding very vital information on the same subject in completely different sections before... The haynes manual is also delightfully incomplete.

For what it's worth, I measured all 4 guides at .313-.314, and all four stems at .309-.310 (caliper is the best I have at the moment so measurements aren't that precise). The three good valves all feel pretty good with minimal slop.

I had asked the machinist to replace the bad valve from last time, but he said he polished it up and it was fine. I wonder if he switched the valves to the opposite cylinders since he did a full valve job anyway? I can't imagine he would put a bent valve back in after what I told him had happened before. All the valves were brand new prior to the first rebuild. It doesn't appear bent when I roll it on a granite block but it doesn't roll straight due to the brass deposit - I'll have to polish that off to check.

If everything checks out I will recondition the parts, reassemble and attempt another go at it.

Final thought on the tuning - my carb has been without a choke since at least the previous owner. He sealed off the cable hole with what looks like JB weld. Never seemed to be a problem though.

RetroRod

Josh,

Depite the reputation of bike repair shops, assume nothing, and expect the worst.

I am assuming you will check valves for seal, a very basic test is to pour kerosene into the head chambers, then check for any signs of weeping.

When you get this beastie going, run an upper cylinder lubricant. Lead would previously have assisted lubrication, and in its absence a little lubricant in the fuel can only do good. RR

pookybear

Josh,

It sounds like you have plenty of clearance with the numbers you
give. But remember that if there is metal on the valve stem it did
come from that guide so it too will need work or replacement.
A slight bend in a valve would cause that for sure. You can without
polishing the stem just roll the valve off of the tulip and the top
of the stem. Then you can watch the stem to see if it wobbles.

Retro has some the right points with lean and rich mixtures and
what the addition of time will do to combustion temperatures. I
try to run my bike with a little bit of a rich mixture. But I do run
the timing a little less advanced. So I do get some blueing of the
pipes and sooting of the plugs. But neither is to any point of
extreme, and runs rather well. It is the far extremes that cause
damage such as holed pistons, and burnt valves.

Pookybear

rousseau

This usually goes without saying but just in case--- Be sure to use some kind of assembly lube. If your guy put it together "dry" It can gall on initial startup.

josh

For sure, I have lubriplate to use for that.

I cleaned up the valve last night, it looks pretty good but there are 3 "dents" about halfway up the stem. They are small, about 1/32-1/16 in diameter, not very deep. They are where the brass had deposited itself on the valve. There are a couple of corresponding grooves in the guide, which I reamed out and otherwise looks very good except for the small grooves about 1/2" long halfway up. They don't look to be very deep. The valve rolls true but the pushrod is bent so I have ordered a new set of tubular pushrods.

Any sense reusing this or is it time for a new guide/valve? I wouldn't even ask but the defects are so small and the rest of the surfaces look very good.

I was thinking more about the tuning, the retarded timing must be what caused this. If the valve is open with still burning gases rushing by, of course they are going to make their way up between the valve and guide. The damage appears to have occurred right where the guide is about 1/8" deep in the iron head, looking from the combustion side. This area is the thickest mass of metal on the head and where I'd expect all the heat to build up, torching the oil and allowing friction heat to build and start melting the brass. Just my two cents I guess.

Oiling might have been a contributing factor. Does anyone know of a good way to figure out if I have good enough oil pressure coming thru the supply lines in the rocker boxes?