I've been following a current post on a T120 with a blown head gasket and have a friend with a similar situation. I measured his head warp at .004" and the local shop wants to skim it but I told him to straighten it after reading it here from J.H. I searched but gave up, thumbed through countless Vintage bikes to no avail so could someone give me the specifics on the procedure please? I'll make up a steel surface plate but need idea on oven temp. etc. Thanks, Mark
Remember these guys are working on a much larger casting, this is a job you learn by doing and failure should always be considered a part of the learning curve.
While slower, I prefer to use an oven. I also keep the temperature closer to 350° F to 375° F rather than the 400°F recommended. The problem is if you get the head too hot you anneal it, and that is not good. I also check the head after one hour. This requires letting it cool. 25 to 30 foot pounds is enough to reverse the bend. It takes a bit of practice! You have to be careful heating a late Triumph head, with replaceable valve seats, more than 350° F as the valve seats could drop out.
If you only have to remove .004" skimming it is an option, but don't forget to check the push rod tube O ring crush which was the cause of the original bend.
If its less than 0.005",I'd consider doing it cold;or at least warm enough to still handle (like drop it into boiling water when its clamped up). I can't see any reason for not using a cylinder barrel as a fixture,with 4 outer head-bolts being fitted at the centre positions on the head. If you put shims(like playing-cards,or gasket material)on the outer parts of the head,just covering the outer bolt holes,wouldn't this work?If you then need to bend (straighten) it a little more,just put in the exact amount of extra shim,and go again. Just a thought.I haven't straightened a Triumph head,but I've straightened a lot of other things (like con-rods).
I can't see any reason for not using a cylinder barrel as a fixture,with 4 outer head-bolts being fitted at the centre positions on the head. If you put shims(like playing-cards,or gasket material)on the outer parts of the head,just covering the outer bolt holes,wouldn't this work?If you then need to bend (straighten) it a little more,just put in the exact amount of extra shim,and go again.
An old cylinder does work as a straightening jig, I straightened a T140 head last year using a junk 650 cylinder just as you describe. My head was bent about .006", so I used .006" and .007" feeler gauges placed at the outside edges of the cylinder as shims, then I heated it in my home oven for an hour at 250F (I was afraid to use a higher temperature). It took out about 2/3 of the warp, and I called it good.
1971 T120RV (R.I.P.) 1973 T140V/TR7 1993 Ducati 900 SS
Thanks Mr. Healy for your prompt reply and the interesting article. Your info is just what I was looking for...I, however, did not know that late heads had replaceable valve seats, I knew the seats looked different but didn't think much more about it, open your eyes grasshopper!
Thanks Pete for your advice, I think I will use a cylinder as suggested, no need to create extra work and since it worked for Eric it should work for me.. .004" ought to pull down without to much trouble.
I wonder how one gets by with welding up the comb. chambers for bath tub chambers and squish bands etc. without ruining the heads. By the time I've welded on a hunk of alum. with much less mass then a cyl. head I've pumped in a lot of heat, well over 500*F I'm sure...makes one think.
"Thanks Pete for your advice, I think I will use a cylinder as suggested..."
Just a word of caution, here. As I mentioned in the previous thread, you want to verfiy the "flatness" of the cylinder, as well. If it is also not within spec, straightening to it will be, at best, a trial and error effort. You still need a surface plate or precision steel straight edge (or better yet, a granite straight edge) to verify that the head is flat. In other words, don't use Susie's plastic ruler. Whatever approach you use, the best end result will be verified flatness within spec for both cylinder and head, and with the proper surface finish. A precision machined straightening plate gives you a tool to check both. Good luck with it!
MarksterTT : The aluminium sections that get really hot (close to the welding) will eventually regain their hardness.The areas that stay below the annealing temperature will still be tough.There will be a heat effected area that does not regain hardness.
If the whole head is later heated to the annealing temperature,it will eventually regain hardness.A lot of hardness returns within 15 minutes,the rest takes about 6 years of ageing.Luckily,it can be artificially aged by heat-treatment much quicker (about a day or so,I think).
My cylinder head has a .006" warp but it seems to be fine and has been fitted for a few years. The bike goes very well indeeed and I see no leaks but what would the symptoms of blowing between the cylinders be? Dave
My guess on shimming is to "over bend" the head as the metal will try to spring back to it's original bent shape when unbolted. I over bent my head with out heating it and got lucky on the first try and I used the cylinder as the flat plate.
1968 T120R 1972 T120RV Any advice given is without a warranty expressed or implied.
Re: Triumph head straightening?
#294720 01/19/106:22 pm01/19/106:22 pm
For those worried about annealing, something to consider is cryogenic treatment. Controlled thermal cycling down to approx. -320 degF where the part is held for roughly 24 hours (sometimes less), then returned slowly to ambient. For aluminum alloy this improves machinability, reduces internal stress, improves crack resistance and hardens the part. While liquid nitrogen is not expensive, the process of controlled cold soaking (so as not to thermally shock the part and cause micro-cracks) requires more effort and time than most home mechanics would be willing to muster. The good news is that cryogenics processors are pretty common these days and often will piggy-back a part or two on another job. For example, they will toss in an aluminum baseball bat for a fairly reasonable amount.
Check the local listings or google cryogenics processors.
I am sure that these folks do this so they can play their vinyl tracks of Sinatra's "It's Witchcraft".
The only possible improvement to the sound of your Strumpet would be to eliminate the "phfffft, phffft, phffft" sound from a leaky head gasket. Otherwise, aluminum alloy cryogenic tempering has become fairly old school in aerospace, sports equipment, and, yes, auto heads. Extremely effective with steel, post heat treating. These properties are measureable. I can't speak to the audiophile market... it there are discernable differences I am certain, at my age, I couldn't measure them by ear... only my wallet.
Re: Triumph head straightening?
#294753 01/19/108:47 pm01/19/108:47 pm
My guess is that there is probably a small amount of elasticity in the aluminum. So you have to go past the point of flatness and have it spring back to the desired flat position. I am going to try it using copper shims. I got about a half dozen warped heads.
Re: Triumph head straightening?
[Re: Bob G]
#294779 01/19/1011:36 pm01/19/1011:36 pm
Pete & Duke, O.K., so I won't rule out my head welding mod before I do a bit more research on aluminum alloy treating & effects of welding..I'm just a little fearful of dropping a valve seat..thankyou both. I do have access to nice new surface plate for checks of flatness so no worries there, but good advice...Mark