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What is the normal operating temperature range for a Triumph 650/ 750 Cylinder head in the exhaust area? I assume this "exhaust area" is the hottest place on the head. I'm fitting pressed in exhaust spigots and would like to figure out how heat expansion will effect my interference fit goal. My educated estimate is approx 250 F.


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Exhaust port will likely be the hottest area, could be hotter than 250F? I have used oversize stubs to repair worn threads, sometimes with screwed pins top and bottom, depending on amount of wear. I am not sure a steel pressed in stub will work due to the different expansion rates, an alloy one may be better? I am sure there is plenty of experience on here.


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Hi Bob, Sent you photo in email. These motors run quite hot. Spark plug is 247f.
Cylinder base is similar.
Oddly some parts of head run cooler. Ambient temperature makes a big difference. The difference between 50 & 100f day is more than 50 degrees. Hotter the day the extra hotter motor & oil gets.
I’m riding tomorrow. We’ll see what we get.


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The late and great Pete R wrote this:

Pete R; exhaust spigots

I've fitted steel spigots to a few of these heads, and I wouldn't tap the head to do it. Threads are more troublesome than a plain interference fit. 
It takes some measurement and fitting, because the hole in the head is usually tapered and slightly out of round. That's not a big problem.
The new spigots match the taper, and fit about 2/3-way in by hand. Just drive them in with a soft hammer. I only ever had one come a little loose, and it does no damage.
It's easy enough to make another one 0.002" or so bigger, or copper plate the old one and drive it back in.

I wouldn't bother trying to cut threads in that head to restore it. If you bore the hole out until it's reasonably round, an interference-fit spigot won't give you much trouble.

I just hammer an unthreaded spigot into a standard, worn, unthreaded port and it stays there.
If the port is oval, make the spigot to the average diameter plus 0.001" or so, and bang it in. If the port is tapered, make the spigot tapered too.


Hope this helps,
SR

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Ah, Pete R
He could explain complex subjects in terms even I could understand. And he did not need a thousand words to do it. He is missed.


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Hi Bob, Emailed you photos of the temp gun readings.
For the readers, start of ride in garage was 56f. Ambient temp 54f on my patio.
After 16 miles of freeway at 65 mph, I forgot to say the last 1/2 mile up a moderately steep hill on freeway, again 65 mph, I exited Lincoln Ave. Off highway 13 in Oakland, CA. Very short off ramp to stop sign. Crossed the street into parking lot. Not even 15 seconds from 65mph. Left motor idle & took a reading on the smooth part of casting on upper of exhaust port. First reading was 584f. I thought maybe vibration of idle was messing with temp reading. I stopped motor. Now reading was 490f. Spark plug was 450-580f. Jumping all over. The gun couldn't settle down, so not valid.
Started motor & continued to John's house down Lincon. He was ready to ride, I didn't stop motor. We rode over the ridge down Pinehurst into the canyons. A little ice on side of road at the coldest spot. Coming into Moraga is easy 35 mph level road, slightly trending down hill, about 2 miles of 35mph. Then into parking lot of Starbucks Moraga.
Stopping motor in 10 seconds I was taking a reading at top of exhaust port 210f. Spark plug 203f.
John & shot the bull & had lunch, 1.5hrs. Outdoors in protected patio in sun we thawed out.
Bikes were in the cold north wind. I'd guess 50f. Head was cold to touch. Exhaust port read 52f. Total ride was 80 miles.
Overall I think the exhaust port was a good 400-450f. I know it's blowing flame out the exhaust port all the time. Especially going uphill at highway speeds.

I've checked John & my bike's temps a few other times. But not directly on the port. I have noticed the motor cools very quickly when it's not working hard. Going about a mile down Lincoln to John's house compression breaking all the way, the motor has over cooled, runs like it's not quite warmed up yet.

So what would the port temp be if you road east towards the valley? In 10 miles you'd be into 100-110f in the summer. I've visited the area several times so familiar with your climate. 110f at 60-65mph for 10 miles no telling how hot the port would be.

Today the oil in frame was just nice & warm to touch. 100f day after the same ride there is no way you could stick finger in oil. You can't even hold finger on curve of backbone. I've done this ride many times & felt the oil & frame many times.

In my mind, you have every right to be concerned about heat expansion of port. I tend to pull my pipes into head tight as I can & secure cross over pipe, the braces to motor mounts & push pipes into mufflers so it's trying to force pipes deeper into head. Loose pipes in head is very common problem with push in pipes, both Triumphs & BSAs. Screw in stubs has their problems, but nothing like push in.
What's going to happen when you ride east to hyw 5 in summer? These motors get smoking hot. They sound like they are going to blow up. The rattles from motor will scare you until you are used to it. Oddly if you don't let bike ping at all & mixture is not lean at all, you have a good high temp oil, the motors take it fine. Next morning it's back to normal.

Very high temp loctite is made that can take these temps. Just a thought. I've never used it. What are your spigots made of?
Don


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My 71 A65 had spigots when I bought it. PO said he used hi-temp JB Weld to mount them. I was cruising down the interstate at about 70mph when one blew out of the head. I pulled over and shoved it back in to get home.
The next day I took it to a friend who installed some small set screws to hold them in. That winter when I had the head off I took it back to him and had the spigots welded in place.
I still don't trust push-in pipes or spigots.


Keep your head up and your stick on the ice.

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I would have to agree with DavidP, my experience tells me they need more to secure them than just interference fit. The temps are too high.


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I wish I could just do what Pete R said, but, everything I do turns out to need special attention-- example ---- these steel spigots have a OD that is .009" larger than the exhaust port ID at ambient temp. there is not way I can just "knock them in"-- I have tested the expansion of the exhaust port at 250F and found it expands .007" ( this will be tested again) . I have dry ice frozen the spigot and found it shrinks .0015" .-- If all this is correct I can turn the spigot down .001" , heat the head, freeze the spigots, get a zero clearance IF and knock them in with very high temp locktite and maybe a plan to set screw them also. These spigots were "Low Brow Customs" sourced and their advice was vague. Fraz Grub said a .004 to .005 IF would be good but there wasn't advice about how temperature will effect the IF. --- thanks guys for your input and I'm still watching this to see who else has experience.


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https://www.shopevengineering.com/

Get it fixed permanently and correctly. They did my 72. Seems to me it was 50 bucks a side, but that was along time ago. Great customer service.


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Hi Bob, how much does the steel expand at 250f?
Too tight you’ll crack or distort head.

It is true, the real cure is thread port & use screw in spigots. My friend had this done. Screw ins have held perfectly for several years & many thousands of miles. He is using crossover pipe with this motor even though thread in spigots. The inner end of spigots must bottom in ports before getting thread bound. If thread bottoms at all spigot will want to unscrew.

I don’t know prices in our area. I don’t know where to have it done now that Rabers is closed.
Don


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i used one pair of tap-in alumi um spigots on my 72 for some 35 years. then one cracked about 6 years ago, and i installed steel tap-in spigots from Lowbrow in america

trouble-free for me.


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Why the obsession about 250F?
The inside of the exhaust port is way beyond that, by another 200F or more.
Imagine the temperature of the exhaust gases at maybe 1000F or more, when allowed release.

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Hi Bob, Codeman got back to me on the spigots he put in '76 Bonnie. They were stainless steel. Used very high temp silicon as a sealant & drove them in. Have held for 4500 miles now.
Don


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250F is just a starting point for this conversation and chosen because I can heat parts in my DIY Moto shop to that temp.
Don-- I will measure the spigot at 250F and thanks for thinking about that-- good idea.


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Hi Koan; but with those temperatures the heads would almost melt

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Hi reverb, Melting temperature of aluminum is about 1220F/660C.
Don


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I have always wondered about this too

If I were to set them up, I would set the spigots up so they would have about .004-.005" press assuming the spigots are steel

Yes, the bore needs to be round prior to installing

The steel spigot will expand with heat too, just not as much as the alloy

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Check with an engine rebuilder and use the same interference fits as they use for valve seats for a given size.

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Don -- spigot expanded .002" at 250F--- went from ambient temp 1.3907" to hot temp 1.3927"---- talking soon with a highly recommended head rebuilder to see what he says on interference fits of valve seats. thanks for that suggestion GeoffLLLL, good thinking


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I don't know if you can compare valve seat interference fit with exhaust stubs....Different metal, different situations......It's my opinion is there some over thinking going on here.... crazy


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