an important reason to buy new head bolts - Alfa Romeo Forum
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(Post Link) post #1 of 45 Old 01-05-14 Thread Starter
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an important reason to buy new head bolts

hi guys

I recently asked about changing the head bolts when changing the head gasket. I got lots of conflicting responses and as a result didn't change them and the head gasket failed instantly.

I have since replaced the bolts and could definitely feel the difference when torqueing them up and doing the angle turns.

I also found this really really good explanation as to why you should always use new head bolts if they are the torque to yield type bolts (stretch type)

Bolt Engineering - Torque to yield and Torque/Angle Tighten (TTY & TAT) - Mickey's RV8 Site
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you are right
if they have to be "angle" tightened they are stretch bolts and should always be renewed.
on a TS it's 40NM +90+90+90deg
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They are not stretch bolts on the Twin spark. You do not need to change them.
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Quote:
Originally Posted by Mitch916 View Post
They are not stretch bolts on the Twin spark. You do not need to change them.
yeah they are they are. hence why they have to be torqued to a specific torque and then tightened in angles.

hence.........

Torque to yield (TTY) bolts, also commonly referred to as angle torque or
stretch bolts, are used in many of today's modern engines predominantly for
cylinder head bolts but also main bearing and big end caps.

Compared to conventional type bolts, TTY bolts offer the engine manufacturer
a number of advantages including greater flexibility of design, reductions
in component costs, more accurate assembly and reliability of seal. Engines
designed utilising TTY head bolts require fewer head bolts to achieve the
desired clamping loads then those using conventional bolts. With fewer bolts
the engine manufacturer has more flexibility in cylinder head and block
design as well as reducing the cost of the engine.

Whilst TTY bolts are attractive to the engine manufacturer, there are
disadvantages to the engine repairer. For the most of us it would be
unthinkable to replace a conventional head bolt unless the bolt was damaged,
i.e. stripped threads, the bolt head was rounded off, the shank was severely
corroded or pitted.

Conventional head bolts simply just did not wear out. Torque to yield head
bolts however, by the very nature of their design, do wear out and should
NEVER be reused.
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I understand that stretch bolts shouldn't be reused.

The Twinspark head bolts are not stretch bolts though. I thouroughly inspected the old ones when I rebuilt my engine and there was no sign of stretching on the final threads. i took advice from people who actually rebuild Alfa engines and to a man they said they are not stretch bolts. I reused mine and have had no issues, these bolts have done over 170K miles.

Last edited by Mitch916; 02-05-14 at 20:29.
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Im the same as Mitch, the tightening sequence is to simply ensure a correct seal between lower and upper engine without damaging gasket. I too have retightened these bolts without issue and my car is also 100k+ mileage. ....touch wood.
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The threads wont (or can't) stretch - a stretch bolt will lengthen in the shank, the unthreaded section between the head and the start of the thread. You could measure the difference in length between a used bolt and a new one to check if they are stretch bolts but the difference might not be great.

If the shank is waisted, that's a pretty good clue that it's a stretch bolt.
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Quote:
Originally Posted by EauRouge View Post
Im the same as Mitch, the tightening sequence is to simply ensure a correct seal between lower and upper engine without damaging gasket. I too have retightened these bolts without issue and my car is also 100k+ mileage. ....touch wood.
I am quite confused by all this, the use of angle tightening to me would seem to indicate stretch bolts, but the Alfa T.Spark Engine overhaul manual makes no mention of fitting new bolts, maybe the angle tightening is just to correctly compress the head gasket. Engine Overhaul Manual
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you can't check a stretch bolt through visual examination. I've tossed no end of apparently good bolts in the bin..
breaks my heart..
you may get away with it, but to be sure, I buy new bolts.
I often wonder if it's the cause of unexplained head gasket failure further down the line.
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I give up. Do what you like, it's your money.

I just wanted to put the record straight for future readers.

Last edited by Mitch916; 03-05-14 at 11:58.
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Ok
the evidence seems to suggest that they are "stretch" bolts.
In that they are sequentially tightened to a specific angle, not torque.
There is no mention of it in the book one way or the other. TAT or TTY
Conventional wisdom indicates that "stretch" bolts should be used only once.
It is up to the individual to decide on whether to re-use or not. (cash strapped or just plain tight)
The OP suffered immediate head gasket failure.
The OP replaced the bolts and fitted a new gasket.
The new bolts/gasket did not fail.
I feel that it would be generally unwise to advise on their re-use.
I agree with the OP.. and thanks for the link it's a good read.

Gettin' to old for this sh*t

Last edited by seadart; 03-05-14 at 15:17.
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u gotta love alfa romeos you really do..........
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(Post Link) post #13 of 45 Old 04-05-14 Thread Starter
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if I had listened to some very wise people on here I would have replaced the bolts first time round saving me the cost of a new head gasket and also the time stripping and recleaning everything. so I wanted to make sure that if anyone else should venture on the same question that they have a better chance of saving the cash than I did trying to do it on the cheap!
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But did you do it correctly in the first place? It might have been a poorly tightened head that led to your 2nd failure? I have reused the same bolts in the same holes and had absolutely no issues.

.....Not wishing to start a handbag fight but, i reckon your failure was down to the job not being correctly done in first instance rather than the non-stretch bolts being the culprit? .........just saying!
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Stretch bolts are only reusable if the manufacturer includes a tolerance spec of the bolt during inspection/refitting. I've only reused stretch bolts fitted to a cam pulley and engine mount. In an engine its not worth the risk
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Its recommended put new bolts. Especially for diesel engines
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(Post Link) post #17 of 45 Old 11-05-14 Thread Starter
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Quote:
Originally Posted by EauRouge View Post
But did you do it correctly in the first place? It might have been a poorly tightened head that led to your 2nd failure? I have reused the same bolts in the same holes and had absolutely no issues.

.....Not wishing to start a handbag fight but, i reckon your failure was down to the job not being correctly done in first instance rather than the non-stretch bolts being the culprit? .........just saying!
I do love your quotes eaurouge! I think I did it correctly but being that it was my first time I cannot rule it out. however I did it this time and it appears to have cured the water problem etc,, now I have different issues im thinking new engine time!!
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The twin spark does NOT use stretch bolts. They do NOT need to be replaced.
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if they are not stretch bolts.. why do you have to stretch them??
I can't find anything anywhere that says they are not stretch bolts..
where's the evidence?? if I see evidence, I'll stop chucking them away..
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Quote:
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if they are not stretch bolts.. why do you have to stretch them??
I can't find anything anywhere that says they are not stretch bolts..
where's the evidence?? if I see evidence, I'll stop chucking them away..
They do not stretch. When you tighten them you do not exceed the point of elasticity. Angle tightening head bolts is a common way of torqueing the head down and not indicative of bolt type. I've rebuilt over 50 twin sparks and never had an issue with them.

Pug / Citroen 1.9's (as fitted to the 205's) use stretch bolts. I've rebuilt a few of them too. They have a helical groove along the shank of the bolt to weaken them so that they stretch when you try to tighten them. You can feel it stretching when you torque the bolt up.

Last edited by Chris155; 15-05-14 at 20:51.
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Quote:
Originally Posted by james1950 View Post
if I had listened to some very wise people on here I would have replaced the bolts first time round saving me the cost of a new head gasket and also the time stripping and recleaning everything. so I wanted to make sure that if anyone else should venture on the same question that they have a better chance of saving the cash than I did trying to do it on the cheap!
Did you clean the threads in the block and bolts out before refitting the head?
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[QUOTE=Chris155;9071034]They do not stretch. When you tighten them you do not exceed the point of elasticity. Angle tightening head bolts is a common way of torqueing the head down and not indicative of bolt type. I've rebuilt over 50 twin sparks and never had an issue with them.

well why don't they just give a straight torque figure then..??
I'm not arguing ,, I'm asking .. trying to learn something here..

Where's the evidence.. where's it written down???..
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Angle tightening is considered to be more accurate than tightening with torque wrench (no influence of friction from threads and/or bolt head).
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Quote:
Originally Posted by seadart View Post
well why don't they just give a straight torque figure then..??
I'm not arguing ,, I'm asking .. trying to learn something here..

Where's the evidence.. where's it written down???..
Welcome to my moron list...

I'm out.
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OK
First thing you have to do is determine whether or not it's a TTY bolt .
It would be nice if it were to mention something about it in the workshop manual , but it doesn't
That leaves MK.1 eyeball and deduction.

The book states that the bolts are first torqued down and then further angular tightening in three stages.
this suggests to me that they are TTY bolts.
The bolts have a reduced shank.
This further suggests to me that they are TTY calibrated bolts.
The OP experienced head gasket failure.
This further suggests to me that they are TTY bolts.
The OP probably had no way of knowing how many times they had been used before or if they had ever been over tightened, and neither do I.
I don't buy the "stretched thread pitch check".. too many variables..

Quacks like a duck, walks like a duck, looks like a duck...

Now there may be something written down in a technical journal that says they are or are not TTY .. Or how many times they can be reused.. But I can't find it. ..
any pointers??

Last edited by seadart; 16-05-14 at 10:29.
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