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Old 02-12-2013, 06:11 AM   #1
Tre900
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Default The tale of two T120 Heads - experienced builders wanted

I have narrowed my options to these two T120 heads. I will send either one I go with out for some clean up but I'm on the fence for which one to use:

The bottom end is 1967: DU50988 - basket case

Head 1: (on the left)
stamped 1968 Mid year
I do NOT have the longer Pushrod tubes
I do NOT have the longer the Tappets
It has one Helicoil already
It requires another Helicoil for one of the exhust rocker box bolts
I do NOT have means or experience to do a Helicoil


Head 2: (On the right)

Stamped 1966 Mid year
Does not have one Exhaust Pipe Adapter: Threads are flat in some spots
Looks to be burnt up pretty good
I DO have push rod tubes from a 65 tr6C which should fit
I DO have tappets and associated bits for this shallower push rod tube hole

Both of these are swap meet specials so history should be taken with a grain of salt.

And lastly Do I have to stick with the associated rocker box for the head I select - that is: If this was your build would you use the rocker boxes with the stud holes or not with a certain head?

Thanks guys - Lots of info here so I appreciate your input. I don't want to send one out to get Valves cut and done only to feel like it should have send the other later.

Tre900
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Old 02-12-2013, 09:27 AM   #2
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Default Re: The tale of two T120 Heads - experienced builders wanted

Dude... means and experience to do a Helicoil are both minimal. Helicoil kits come with the proper tap and the little driver. All you need is a drill and a small tap handle. They are extremely easy to install. Trust me... you can do this.

When I was young and timid, my uncle and mentor once told me "Boy, you ain't good enough to fuck somethin' up so bad that I can't come and fix it. Now have at the goddam thing!" Those words have served me well for nearly 40 years now.

Now... it has become extremely "internet cool" to say shit like "Helicoils are shit. you need a ___________-sert instead." I'm not smart enough to know about shit like that; but I've installed Helicoils for over 30 years now, in everything from lawnmower engines to big-inch all aluminum dragrace engines and have never had one fail.... ever.

I'm not qualified to say which head would be better on your Brit bike. Best of luck going forward.
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Old 02-12-2013, 09:36 AM   #3
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Default Re: The tale of two T120 Heads - experienced builders wanted

^^what he said
I know many Vincent motors fixed with JB Weld too
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Old 02-12-2013, 10:21 AM   #4
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Default Re: The tale of two T120 Heads - experienced builders wanted

tre900,those numbers you mention are not stamped, they are casting dates cast in the head. As a rule they run a year before the model year of the motor. So that "66" is a 67 year model head. If it were mine,I'd try to use that one. Mixing different year parts can create headaches that will make doing a Heli-coil seem like fun. Jack
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Old 02-12-2013, 01:48 PM   #5
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Default Re: The tale of two T120 Heads - experienced builders wanted

Thanks for the input Jack. I guess I had it in my mind that the later heads were "better".

I thought if I got a lot of feed back from this thread to that degree I would do the extra work on that head.

Right now though, it looks like I should just go ahead and use the one you suggest simply because I would have less repair work to do.

Looks like I need to search the effort for a exhaust port repair.
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Old 02-12-2013, 01:51 PM   #6
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Default Re: The tale of two T120 Heads - experienced builders wanted

Use the earlier rocker boxes, they will work with both of those heads. Then pick the head that has the least valve seat recession.
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Old 02-12-2013, 03:10 PM   #7
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Default Re: The tale of two T120 Heads - experienced builders wanted

Thank you!

Would that be the distance between where the valve and head met looking at it upside down?
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Old 02-12-2013, 05:03 PM   #8
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Default Re: The tale of two T120 Heads - experienced builders wanted

That would be the one with least amount of a ridge running around the flat surface where the valve seals. As heads heat up and valves open and close they eventually start to erode the seat it closes into. That's where the term "recession" comes from.
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Old 02-12-2013, 06:30 PM   #9
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Default Re: The tale of two T120 Heads - experienced builders wanted

No valve tool- fail. Can i use anything besides triumph valve spring compressor tool?
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Old 02-12-2013, 06:42 PM   #10
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Default Re: The tale of two T120 Heads - experienced builders wanted

Crap, I don't have any pictures to show, but I made a Triumph valave spring compressor from a 5.00 Harbor Freight big "C" clamp and a 1 1/2" section of 1"x1" square tubing with a couple of mouse holes gacked in it. Hope fully some one will show a picture of the same.
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Old 02-12-2013, 07:12 PM   #11
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Default Re: The tale of two T120 Heads - experienced builders wanted

I took what you suggested and got a video from You tube so now I"m armed and dangerous. Heading to the workshop. Thanks NL
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Old 02-12-2013, 07:33 PM   #12
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Default Re: The tale of two T120 Heads - experienced builders wanted

Keep in mind that "oversize" ex. stubs are available,They are oversize on the thread only. Jack
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Old 02-12-2013, 09:17 PM   #13
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Default Re: The tale of two T120 Heads - experienced builders wanted

Built a Valve spring compressor using a rope crimper.

Here's what the heads look like.
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Old 02-12-2013, 10:05 PM   #14
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Default Re: The tale of two T120 Heads - experienced builders wanted

You are BY FAR crafty enough to install a Helicoil.
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Old 02-12-2013, 10:26 PM   #15
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Default Re: The tale of two T120 Heads - experienced builders wanted

Quote:
Originally Posted by Tre900 View Post
Built a Valve spring compressor using a rope crimper.

Here's what the heads look like.

'Zactly what I had in mind! Way pass!

Quote:
Originally Posted by Nottso View Post
You are BY FAR crafty enough to install a Helicoil.
Absatively!!!

As far as the exhaust spiggots go, I used a pair of oversized aluminum units that pressed into the head and were welded to the head it's self. I then went back in and blended the leading edge into the port so there wasn't any sort of disturbance in flow. They worked well in my avatar bike, but I'm not quite sure how the more experianced guys on the board feel about them.
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Old 02-12-2013, 10:33 PM   #16
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Default Re: The tale of two T120 Heads - experienced builders wanted

It's kind of hard to tell what kind of shape the seats are in from a photo because it really doesn't show demension. If the shiny seat areas have a sortof ridge around them, that is seat recession. You could machine it out to flat, but then the valve is pulled deeper into the head and flow, valve adjustment, and even valve train geometery can be effected. If it's extreme, machining it flat and going to a slightly larger valve can restore some of the height lost. Might not be completely Kosher, but it worked for me.
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Old 02-13-2013, 04:46 AM   #17
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Default Re: The tale of two T120 Heads - experienced builders wanted

Quote:
Originally Posted by Tre900 View Post
Built a Valve spring compressor using a rope crimper.

Here's what the heads look like.
There you go! Hell of an idea. Yeah, you'll have no trouble with doing a helicoil.
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Old 02-13-2013, 05:08 AM   #18
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Default Re: The tale of two T120 Heads - experienced builders wanted

Would the "valve train geometry" being negativity effected cause one of the bottom cups to stick to the Valve Guide? I have one that won't break free. I didn't want to use too much force since its a tight fit in place.

I guess my next step is to continue to strip these heads down and get them clean to get a better look at what's happening.

Should I remove the exhaust pipe adapters that are in place? Heat the head and put a bar through the holed and twist I assume? I would hate to strip out the ones that are connected.
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Old 02-13-2013, 08:23 AM   #19
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Default Re: The tale of two T120 Heads - experienced builders wanted

Quote:
Originally Posted by need louvers ? View Post
Crap, I don't have any pictures to show, but I made a Triumph valave spring compressor from a 5.00 Harbor Freight big "C" clamp and a 1 1/2" section of 1"x1" square tubing with a couple of mouse holes gacked in it. Hope fully some one will show a picture of the same.
Here's my rig.

Grind the side of a 1/2" drive socket. That way the clamp part goes down in and is a little more stable and wont slip off.


Put a felt pad on the valve face side of the clamp so nothing gets dinged up.


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Old 02-13-2013, 11:41 AM   #20
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Default Re: The tale of two T120 Heads - experienced builders wanted

Quote:
Originally Posted by Tre900 View Post
Would the "valve train geometry" being negativity effected cause one of the bottom cups to stick to the Valve Guide? I have one that won't break free. I didn't want to use too much force since its a tight fit in place.

Should I remove the exhaust pipe adapters that are in place? Heat the head and put a bar through the holed and twist I assume? I would hate to strip out the ones that are connected.
The valve-to-rocker geometry is not badly effected by a small amout of seat recession,1/16" or so.At lower rpm,it's actually an improvement (more square at mid-lift).That didn't cause the spring collar to stick.The shoulder on the guide might just be too big in diameter.

All your lower spring collars should measure 0.165" thick at the inner spring seat,if you're using those '68-onward valve springs (They are good springs,the outers should measure 1-5/8" long.You'll get by with shims if they've only sunk 1/16".Use the longer springs on the exhaust.)
If you can get 65lbs INTAKE seated load,70-75 lbs EXHAUST,you should be OK.Measure the spring loads when the head is re-assembled.Use bathroom scales to measure it.

Don't even think about trying to remove tight exhaust spigots.If they've been properly fitted,you will cause big damage.Boring them out and cutting them to pieces is the only safe way.Don't think about using aluminium spigots.Triumph tried this for a short time,and quickly reverted (as far as I know,none survived).

I'd be happy to use the '69 head.You only need to get correct thickness pushrod tube seals.Crush on the seals should be 0.030"-0.040".
'66 used 3/16" lower seal,1/8" upper.Later bikes used a 3/32" section viton O-ring at the top.I've used O-rings top and bottom to get correct crush.

At least the '69 head uses 1/4" UNC threads for the rockers,instead of 1/4" x 26 tpi on the early head.1/4" UNC helicoils are cheap and easy to find.'69 intake ports are supposedly better.

If a head (pre-'72) has no seat recession,the exhaust valve collet groove will be 1-3/8" above the head surface,1-7/16" for the intake valve.1/16" recession is acceptable,even a little more if you shim the valve springs.Never cut into the aluminium hemi doing a valve job.Replace the recessed seats before it ever gets that bad.

Another deciding factor would be how flat the head surfaces are,and whether either head had ever been milled flat.Measure the overall thickness.Try to avoid using a head that's ever been milled.A slight bow (0.005") will usually pull down flat and cause no problem.A head bowed 0.010" sometimes works OK.A head can be straightened using heat,avoid milling.A milled head will mess up PRT seal crush,and too much crush will bend the head again.A milled head can give you too much compression.

If there is still a trace of exhaust spigot thread left in the head,you could cut it deeper with a 60 degree tool made from a countersunk allen screw and powered by a pistol drill.Then fit an "oversize" spigot.The inner face of the spigot must pull up hard against the head.You normally need to relieve the spigot threads at either end to achieve this,or it will come loose and flog out again.

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