Head Bolt Failure (Page 1/4)
Notorio DEC 21, 01:55 AM
I fear I am in deep do-do here. Looking for some torque specs for my 2.8 I pulled this Table from the Forum. Given the huge range of 65-90 ft-lbs I elected to tighten my new bolts to 80, going in steps around the head from snug, to 20, 40, 60, then finally 80.



Here is the sheet I was using to manage the tightening sequence.



I had the Odd bank up to 60 and was finishing the Even bank when the last bolt, #8, suddenly gave way during tightening. I unscrewed it from the head and immediately saw that some of the threads had been sheared off, or rounded over. This picture shows that the 'polished' looking end threads now have a smaller diameter than the upper threads.



I have another new bolt spare that I could try but I am loath to do anything that might make the situation worse. All these bolts are M11 x 1.5.

Any suggestions?

[This message has been edited by Notorio (edited 12-21-2019).]

wftb DEC 21, 08:47 AM
You need to check the threads in the block for damage. It sounds to me like the bolts have bottomed out and then the threads got damaged on the last twist. I always buy ARP studs and bolts for cylinder heads and connecting rods. Comes with lubricant and specific torque values for the engine you are working on. Expensive but worth it.

------------------
86 GT built 2.2 ecotec turbo
rear SLA suspension
QA1 coilovers on tube arms

cvxjet DEC 21, 11:46 AM
I have the 85 manual and it says (In the same format) that the torque spec is "65-75".......(On my 460 Ford in my jetboat they go to 140!) Did you chase the threads with a tap before?

If you can wait until Monday I can ask my Engine builder friend what he recommends....He builds absolutely everything- even sleeving blocks for numbers-matching builds. Has built drag race engines, etc...

By the way, your pic of the bolt did not show up....
Notorio DEC 21, 12:47 PM

quote
Originally posted by cvxjet:

I have the 85 manual and it says (In the same format) that the torque spec is "65-75".......(On my 460 Ford in my jetboat they go to 140!) Did you chase the threads with a tap before?

If you can wait until Monday I can ask my Engine builder friend what he recommends....He builds absolutely everything- even sleeving blocks for numbers-matching builds. Has built drag race engines, etc...

By the way, your pic of the bolt did not show up....



Doh! Picture should now be there ...

I'll keep the stud idea in mind. Turns out that this is a through-hole into the water jacket, so no 'bottom' per se. All the threads were chased. Yikes, the heli-coil kits expensive ($50-60) for just the one M11 x 1.5 size but looks like an option even for a through-hole.

New data ... the original Pontiac bolt was a bit bigger (10.95) so I tried that to see what would happen. Same story, tightens nicely to about 40 ft-#s but above that starts spinning. Whatever the repair method will be I'd better order another head gasket and pull the head to examine the threads.

'Wait til Monday...' if we don't hit on a good solution over the weekend I shall certainly be thankful to hear what your engine builder friend has to say

Dennis LaGrua DEC 21, 01:00 PM
IIRC, the head bolts on the 2.8L are Torque to yield. This requires replacing them with the same bolt. Also when replacing head bolts you should chase the threads in the block with a tap and then clean them out.

[This message has been edited by Dennis LaGrua (edited 12-21-2019).]

olejoedad DEC 21, 02:33 PM
The head bolts are not torque to yield.

The chart you referenced is from the FSM, but it should be noted in the assembly instructions, the FSM calls for a head bolt torque spec of 66 ft.lbs.
cvxjet DEC 21, 04:24 PM
I just checked my manuals; I have an 88 and an 85- both say in the actual 66 Lb Ft in the assembly instructions.....The Haynes manual says the "65-75" for 85-87 and "65-90" for 88 Fieros.....This is very confusing and also, >65< to >90< is a very wide spread.

90 N.m = 66 Lb Ft which may be the root of the confusion......
Spadesluck DEC 21, 07:42 PM
When rebuilding my 2.8 last year I broke a head bolt, was not very happy about it, just torquing it down. I would err on the side caution and use the lower end of the torque scale.

[This message has been edited by Spadesluck (edited 12-21-2019).]

fierogt28 DEC 21, 09:05 PM
If I would / will be doing a rebuild buy new bolts for piece of mind. Its not expensive.

You don't wanna worry about head bolt failure. If you have 2500$ in a rebuilt engine, I don't think 150$ of head bolts will bother your
wallet. May not be torque to yield bolts, just buy new ones...go with Fel-pro, ARP or GM.

There's one bolt that has a stud end to it.

Go with the FSM torque spec. Its always better to get an exact spec than a wide variation torque spec (example 65-90ft/lbs).

------------------
fierogt28

88 GT, Loaded, 5-speed.
88 GT, 5-speed. Beechwood interior, All original.

Spoon DEC 21, 09:16 PM

quote
Originally posted by cvxjet:

I just checked my manuals; I have an 88 and an 85- both say in the actual 66 Lb Ft in the assembly instructions.....The Haynes manual says the "65-75" for 85-87 and "65-90" for 88 Fieros.....This is very confusing and also, >65< to >90< is a very wide spread.

90 N.m = 66 Lb Ft which may be the root of the confusion......



That "65-90" FT-LBS is not a choice of either or. It's a 2 or three step process. In this case the 1st go around would be 65 ft lb. and the second would be the final torque of 65 ft lb.
To remove any doubt I clipped the following from a web site.

[COLOR=#3333FF]PASS 1: Torque to a maximum of 30% of the final torque value in accordance with the torque sequence. Check that gasket is getting compressed uniformly.
PASS 2: Torque to a maximum of 60% of the final torque value.
PASS 3: Torque to the final torque value (100%).
[/COLOR]

Hold on here we go.
https://hardhatengineer.com...rque-sequence-table/

Spoon

------------------
"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

[This message has been edited by Spoon (edited 12-21-2019).]