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Discussion Starter · #1 ·
So I took my head to the high end machine shop in town here and paid a weeks salary to get it done and now I am not too sure if I got what I paid for. I am putting this head on a big bore kit so I decided it would benefit from some extra work so I got the oversize intake valves and a five angle job on the exhaust. Now the valves seem very deeply set (my hot rod buddy calls it shrouded) and there are sharp corners for the gas to flow around. Should I dress out the ridges or have a porting guy do it? What about the loss in compression if I do that? Skim the head to get it back?

Here are some pictures:







Thoughts?
 

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Discussion Starter · #4 ·
Thanks guys, it is a street application but everything I had read saying it was not worth the 750 kit without doing the head as well and now I doubt all that work on the head will be of any benefit, and I know the TR6 is not as good for power as the bonnie head but I am using a two carb HHP manifold. So what`s the conclusion run it the way it is or blend out the pockets...
 

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I simply don't understand where this idea came from that 100 more cubic centimeters, properly tuned is not going to help your motor go faster. It boggles my mind how this information has gotten loose and people are believing it. So I am hearing you say that somebody told you with a straight face that a 750 kit on your Triumph is of no value without porting your head? I have also heard that big bore kits "don't work" without bigger cams. I am on record as saying this is just total misinformation. I think Sonny Routt is still alive, lets ask him if his drop on big bore kits were just a cleverly conceived scam to get people to buy them without any horsepower gain.

ALSO: Never, never never take your Triumph head to a car machine shop unless the owner owns, rides and rebuilds his own Triumphs. I don't know if this is the case with your head, but everyone should bear it in mind.
 

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I simply don't understand where this idea came from that 100 more cubic centimeters, properly tuned is not going to help your motor go faster. It boggles my mind how this information has gotten loose and people are believing it. So I am hearing you say that somebody told you with a straight face that a 750 kit on your Triumph is of no value without porting your head? I have also heard that big bore kits "don't work" without bigger cams. I am on record as saying this is just total misinformation. I think Sonny Routt is still alive, lets ask him if his drop on big bore kits were just a cleverly conceived scam to get people to buy them without any horsepower gain.
hence the phrase, "there's no replacement for displacement"
 

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I simply don't understand where this idea came from that 100 more cubic centimeters, properly tuned is not going to help your motor go faster. It boggles my mind how this information has gotten loose and people are believing it. So I am hearing you say that somebody told you with a straight face that a 750 kit on your Triumph is of no value without porting your head? I have also heard that big bore kits "don't work" without bigger cams. I am on record as saying this is just total misinformation. I think Sonny Routt is still alive, lets ask him if his drop on big bore kits were just a cleverly conceived scam to get people to buy them without any horsepower gain.

ALSO: Never, never never take your Triumph head to a car machine shop unless the owner owns, rides and rebuilds his own Triumphs. I don't know if this is the case with your head, but everyone should bear it in mind.
The key phrase here is proper tuning! My friend has a stock 650 and a big bore 750. 650 eats the big bore all day long. I have also riddin big bore bikes were the big bore kit threw the balance off so far that you couldnt use the extra power due to the vibration. Obviously properly set up a big bore will add more power, but it seems to me if u want to see a significant power increase a few more mods wont hurt.
 

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Discussion Starter · #10 ·
Thanks for weighing in Wes, I appreciate the wisdom of everyone on the board. I realize I will get some gains just from the larger displacement but the head needed doing so I was trying to get the best bang for my buck...

I took the head back to the machine shop (who only does bike and ATVs) and the owner proposed installing new seats but he wants to know the installed stem height but all I can find in the books is the fitted spring length. Is the stem height just a function of this or is there another number floating around out there that I haven't found yet?

Thanks for everyone's advice.
 

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think about it before you have the new seats put in....the old ones are cast into the head and therefore requires surgery to remove....aka, hogging the hell out of the head....i will provide pics of what a mess it will look like.....now it sits on my shelf collecting dust and is a reminder for next time to just send it to someone who knows Triumphs.....
 

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Ive seen several replacement seats come loose, the procedure for putting new seats in is to cut the new seat hole right into the existing cast in hat shaped Triumph seat.
You are asking for possible problems with replacement seats. Just leave it, it does not appear those valves are not sunk in there that baddly.
 

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Yeah, dont take a britt bike to a jap shop!! Or Euro shop!!! Fouraces is the man!!

I would run it but check the stem hight, Low end to mid rage to lower upper end will be fine.

One of my 500 triumphs ran great with one Mikuni carb, but crappy with the one amal, Had good gas mileage with the amal though.....

....Roach.
 

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i believe i would just dress the sharp edges off...not so much about flow, more about eliminating a "hotspot".. any radius will dissipate the heat better than a sharp edge!
and doublecheck stem height [ala;wes]
 

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Its hard to tell from the pics... Just how shrouded are the valves? Would it take some "lift" to just get them un-shrouded? before you start installing anything you may want to rig up something that can open the valve while you measure with a dial indicator or just a mike on the stem how long it takes to get to the point where you get flow... You may be loosing a considerable amount of "lift" from your cams. may run like you have flat lobes.... But again its hard to see from the pics clearly.
 

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Discussion Starter · #17 ·
It was hard to photograph (and measure) but I would say the bottom of the valve is at least .040 from the surface of the combustion chamber. So I see what you mean about losing lift.

I am still looking for an installed stem height if anyone knows?
 

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The way you are gonna find out where it needs to be is to measure for the installed spring height. Assemble the valve, shims if any, spring hat and keepers without the spring and measure from spring seat to seat.

The T-120 workshop manual says (A little confusing)
free length Outer 1 1/2".. Inner 1 17/32"..
Fitted Length, Inner ( I am assuming by the way the book reads they mean intake) outer spring 1 3/16... inner spring 1 1/8... Outer ( again assuming exhaust) inner spring 1 7/32"... outer spring 1 5/32"..
Total fitted load, valve open inlet 143lbs.. exh 155lbs...
valve closed inlet 75lbs.. exh 87 lbs

Hope any of this helps.
 

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You can theorize it for several more months or you could put it back together and see how it runs.
Some of the best running triumphs I've ever owned had the low lift 6T cams and 7.5 to one pistons.
 

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The T-120 workshop manual says (A little confusing)
free length Outer 1 1/2".. Inner 1 17/32"..
Fitted Length, Inner ( I am assuming by the way the book reads they mean intake) outer spring 1 3/16... inner spring 1 1/8... Outer ( again assuming exhaust) inner spring 1 7/32"... outer spring 1 5/32"..
Total fitted load, valve open inlet 143lbs.. exh 155lbs...
valve closed inlet 75lbs.. exh 87 lbs
It would be dangerous to believe these specs.They supposedly apply to '68 onward springs,but these figures were never used in production.The outer spring measures 1-5/8".Seated loads were more like 60 lbs intake,65lbs exhaust.You can easily check that with bathroom scales,once the valves are fitted in the head.
Even on a fairly serious engine,shimming the springs to 65lbs intake,75 lbs exhaust is enough.
At 87 lbs seated,the exhaust spring is getting close to coil-bind with standard cams.If you're lucky it will be 1/16" from coil-bind,which is just enough.At 87 lbs,expect cam wear.
The Triumph manual does have mistakes.Another example is big-end nut torque.It has been 22 ft-lbs since June '69,on 500 cc and 650cc engines.It was covered by Service Bulletin 317 July '69 after the introduction of UNF big-end bolts.The figures in the manual were never changed and remained at 27 ft-lb (500cc) and 28 ft-lb (650cc).

On heads before '72,the valve tip will be 1-11/16" from the head casting if the valve is not sunken.Oversize valves should be longer overall,or you will have trouble with this.Sinking the valves deeper in the chamber is not the best way to solve the problem.
The outer edge of the seats should be 0.020"-0.030" smaller diameter than the valve-head.The seats should be 1/16" wide intake,3/32" wide exhaust.
 
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