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head bolts and the book

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head bolts and the book
#1
  This topic is about my 1977 Triumph TR7
old guy Avatar
old guy bob k
sparta, tn., USA   USA
The book says the head should be torqued at 55 fb , that sounds low for a head bolt. What do the rest of you guys set yours at?

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Darth V8R Avatar
Darth V8R Vance Navarrette
Beaverton, OR, USA   USA
1980 Triumph TR8 "Wedgie"
In reply to # 1509556 by old guy The book says the head should be torqued at 55 fb , that sounds low for a head bolt. What do the rest of you guys set yours at?

Remember that the head is aluminum, and over torqueing will crush the head.

55 lb-ft is a typical value for aluminum, particularly when it is plain vanilla cast aluminum. You can go higher with heat treated hyper-eutectic alloys because the are harder, but the TR7 aluminum alloy is nothing special.

I have read, however, that because the head bolts are not perpendicular to the block deck, you can go 5 lb-ft higher than spec to reduce the tendency of the head to warp. Supposedly this was the factory solution to chronic head warpage problems when engines were allowed to overheat. That, and the low coolant sensor warning light are the supposed fix. But that is just what I read someplace. It might have been in "Triumph TR7 - The Untold Story". Or not. confused smiley

YMMV.

Vance



1980 Platinum Metallic TR8, navy blue interior
Bare metal respray, Crower cam, raised compression
ported heads, modified Zenith carbs, 0.060" overbore

gerald4247 Avatar
gerald4247 Gerald Davies
Ventura, CA, USA   USA
I also go with the 55 lb-ft, it seems to work okay..However I do check the torque periodically and sometimes find they have backed off a little, so I torque them again and all seems well.

Good luck
g

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old guy Avatar
old guy bob k
sparta, tn., USA   USA
Thanks for the reply. I realize you are correct and remembered that my !500 midget has only 50 lb on it's head bolts. It just seems that it should be more but maybe that's on cast iron head. I had to get the TR's head shaved 6k to get a flat surface again so as soon as I can get the shavings out and the head gasket in the mail it will go back on the block.
Thanks again.

mcmahontr7 Chris McMahon
Fort Worth, TX, USA   USA
I replaced my head bolt studs with grade 8 bolts. 55ftlb torque works great. Never had a blown gasket. Every once in a while I will retorque it when warm not hot. Still going strong 20 years later last rebuild.

Chris

ozkippy Michael Kip
Emerald, Victoria, Australia   AUS
1976 Triumph Stag "Staglet"
1978 Triumph TR7 "Yellow Wedge"
1979 Triumph TR7
Bob,
60 thou is quite a lot and I'm not sure if the thicker gaskets will take up that much as 'I think ' the thick gaskets are 20 thou thicker. Regardless you may have to look at valve timing being affected.
Copy paste this below from another forum post

You measure the head height (using vernier calipers) from the bottom of the half moon shaped cutout on the end of the head to the head surface. The minimum head height for use with a standard gasket is 112.4 mm or 4.427 inches. If it is less than this, you should use a thicker gasket.

Rimmer Brothers in the UK have .020in (.55mm) thicker head gaskets in stock, Part No GEG3304XT.


Michael

POW Peter Wirth
HEBRON, NH - New Hampshire, USA   USA
In reply to # 1509587 by gerald4247 I also go with the 55 lb-ft, it seems to work okay..However I do check the torque periodically and sometimes find they have backed off a little, so I torque them again and all seems well.

Good luck
g

I'm quoting this particular post only because "they have backed off a little" is used. The terminology is common but I don't really. think the bolts are actually unwinding any. I think more than likely as the block and head both expand just a bit from normal heat, the composite gasket is squished a little more than when first torqued. The engine cools and the block/head relax but the gasket remains just a bit thinner. Re-torquing the head when cool restores the correct torque. Depending on the gasket this can take a couple of cycles until there is no more squish-ability left in the gasket making re-torquing at last unnecessary.Replacement Norton motorcycle head gaskets can be had in either a soft copper or of composite. The copper equipped engine gets torqued on assemble, run up to temp (a good 5-10 mile ride) then re- torqued the following morning when the engine is stone cold. That's it, but we do go through the procedure one more time just to be sure. There is very, very seldom anything to be gained. When using a composite gasket, after initial torquing, the engine is left overnight without ever being run. The next morning, re-torquing will yield results simply because the casket has squished on it's own. These composite gaskets take two or three cycles to settle down. My TR8 uses thin sheet steel head gaskets with raised areas around all the critical areas. Obviously as this steel sheet is very stable. It's not going to compress and once bolt torque flattens the raised areas A single re-torque after one heat cycle and done.

I think those of you using an extra thick head gasket would need more "after heat cycle" re-torquing sessions, maybe three or four for the gasket to reach it's final dimension and settle down.

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Darth V8R Avatar
Darth V8R Vance Navarrette
Beaverton, OR, USA   USA
1980 Triumph TR8 "Wedgie"
In reply to # 1509893 by POW
I think those of you using an extra thick head gasket would need more "after heat cycle" re-torquing sessions, maybe three or four for the gasket to reach it's final dimension and settle down.

In the case of the TR8, using the thicker head gasket lowers the compression and reduces HP unless you have the later heads that were changed (smaller combustion chambers) for the thicker head gasket.

A nice stealth mod would be the later heads with the earlier steel gasket.

Vance



1980 Platinum Metallic TR8, navy blue interior
Bare metal respray, Crower cam, raised compression
ported heads, modified Zenith carbs, 0.060" overbore

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