nervous

[scottt]

Hey guys,

After weeks of butting heads with my extended warranty company, I finaally got them to agree to replace the head gaskets on my 97 STS. The downside is the dealership that sold me the car (which is not a Cadillac dealership) is doing the repairs. Is this something an everyday mechanic can handle?

Thanks in advance.

[K2K]

Head gasket?

If it's just a simple blow, no stripped bolts, then yes, any average mechanic can.

But if it was one of the fairly rare, fairly common head gasket blows where it strips every bolt on the engine and they need to be rethreaded by hand... I'd stick with the dealership. I'm sure you'd have heard if it's the latter, however, so I'm sure you're fine.

[Ranger]

From what I have read on this board, don't let them touch it if they are not familiar with the Northstar (doubtful if not a Cadillac dealer). Also be sure they timesert the head bolt holes or you'll be back in a year or two (something a non-Cadillac dealer may not be aware of).

[Scotty]

I would time sert the block and not install any bolt into a non-time-serted bolt hole. Once the bolt is removed it removes material. It is my understanding that you will be back quickly again for head gaskets if the engine is not time-serted. Also, make sure that they replace the head bolts. Mike

[Bob D]

Scott, the following was written by a GM powertraine engineer with 32 years on the job: (You can find much more in the archives here, under "timeserts") Pay particular attention to posts by 'bbobynski', or 'bill'...

PS, make sure the mechanic that is assigned the job understands "torque angle" procedures, rather than just 'torqueing'. This is vitally important to achieve the correct results for the head to block interface.

>"Head gaskets and new head bolts. Use the OEM gaskets which come with the bolts. The bolts are only to be used once because of the thread locker and lubricant appllied to the bolts when new. The front cover gasket should be OK to reuse.

Personally, as long as it is down that far I would do both sides. Something obviuosly caused the head gasket to fail on the rear side so whether it was corrosion or whatever it may have occurred on the front, too. If just one head bolt has pulled the threads for some reason on the rear then the extra work may not be justified. I guess maybe I would pull the rear off, look at the situation and see if the same failure/problem is likely on the front before deciding whether to do both.

The modified head bolt torqueing procedure is a small change and you will be fine with either, actually. Be sure to use new bolts, use the torque-angle procedure to tighten the bolts and do so in the correct pattern. Do not lubricate the bolts with any thing. The factory applied coatings are designed to lubricate, seal and thread lock. Nothing else is required.

Use only the time-serts that you have mentioned. All thread inserts are not the same not do they perform the same. "timeserts" is not a euphemism for helicoils or anything else. Use only TIME brand timeserts SPECIFICALLY FOR THE NORTHSTAR ENGINE. The normal timeserts are too short and will pull out. There are special Northstar headbolt timeserts.

The Time-Serts, for whoever asked, are hardened steel sleeves

that are threaded on the ID as a replacement thread and on the OD

as a special thread that matches the Time-Sert repair tap. If

the threads are stripped in the aluminum hole the old threads are

drilled out, the hole is tapped with the special repair Time-Sert

tap, the Time-Sert insert is installed by screwing it into place

and the original bolt is reinstalled into the hole threading now

into the ID of the Time-Sert.

Generally speaking the Time-Serted holes are stronger than the

original, virgin holes and are much more resistant to wear if the

head is going to be changed frequently (like on a race engine).

The other brand of thread repair inserts (such as the popular

HeliCoils are not adequate for the repair of the NOrthstar head

bolts as the inserts available are not long enough (not enough

thread engagement on the OD) and the helicoils are not a solid

sleeve rather a slinky or coil of threads which does not hold as

much load since the load on any given thread is not distributed

over the length of the insert. Been there, done that, won't work.

Personally, it is perfectly fine, even desireable, to Time-Sert

all the head bolt holes as a matter of fact on a head gasket

repair. The holes definitely won't strip and the thread

strength will be improved. It is a lot of work but once set up

and doing it , it is cheap insurance. If I built a performance

engine that I knew I would be periodiaclly disassembling I would

Time-Sert every threaded hole from the beginning. On a

production engine, however, that 99.9 % of which never get

disassembled the time-serts are a waste of time and money and not

necessary.

It is very standard practice in the automotive industry to make

threads in the parent aluminum block or head and use for

fasteners. There are very few if any inserted threaded holes in

aluminum blocks and heads."<

[adallak]

virgin holes

guys what are you talking about?

[Barry94]

I also cannot stress the importance of using Timesert inserts on all the head bolt holes.

I know from experience. Removing the heads once is work enough. Twice is torture.

[Greg P.]

I'd ask if they'd ever done a head gasket on a Northstar before.

And definitly make sure they ues the timeserts. Accept no substitutes.