: Concerns in the middle of headgasket repair!
08-26-10, 02:01 PM
I've an 2000 DTS 104000, and the headgasket blew. Now that the shop has the headgaskets off they called me in to show me some things. Biggest issue was the amount of "play" of the pistons inside the cylinder walls. We're able to rock the pistons around inside the cylinder walls, everyone of them. Is this something to worry about. The shop sorda suggested I put another motor in it YIKES! I dont have excessive oil consumption, nor do I have piston slap. I've never had a northstar apart so Im wondering is this something to worry about. I still have the honing patterns in everyone of my cylinder walls also. Second the shop also seems to think that I shouldnt do a thread repair kit on the threads as the threads look wonderful and all were tight to spec. Its a 12mos 12000 mile warranty on the job. I need honest, knowledgeable opinions here. Thanks in advance guys!
08-26-10, 03:09 PM
Do the thread inserts or studs. There's no sense putting it back together otherwise. (If all the bolt holes were good, what made you disassemble the engine ???)
Get in touch with Jake at www.northstarperformance.com or Mile Lawson in Lexington, KY (search) concerning piston skirt clearances.
08-26-10, 03:29 PM
I don't remember rocking the pistons. Cleaned up the pistons ( not carbon buildup but loose dirt that blew around ) but didn't notice anything unusual.
I'm going with the engine ran well before, no piston slap or oil consumption, leave it as it was.
It's unusual for none of the bolt holes to show damage if the HG's leaked. Years ago someone did their heads, no inserts, and had the threads pull on the last bolt! The advice has always been to do them all if you have it apart.
It's the shop that is guaranteeing the job ( at least for one year ) I can see where they might want to go with the original threads.
What were your original symptoms? Did you have this repaired at the first signs of HG problems?
08-26-10, 03:30 PM
Although one HG and 2 plenum replacements does not make me a northstar expert, I have worked on alot of engines over the past 35 years or so. I have seen a few where the pistons seemed to be a loose fit in the bores. With no other symptoms, and the fact that northstars rarely if ever need rebuilding, I would just leave that issue alone. As mentioned above, install the inserts or studs, or you will be revisiting the inside of that engine again.
08-26-10, 05:16 PM
I agree with whats been said already. Install inserts or studs or you'll be in the same boat again. I don't know what to say about the pistons though.
I would not open a Northstar and put the heads back on without inserting the block. I am aware of one guy who did that (not knowing any better) and had to do it again in 10K.
I have a feeling that these guys are not familiar with the Northstar and what they are seeing may be normal, but just don't know it. Talk to Jake.
How long are you going to keep the car? If you are in it for the long haul, I agree with the "always insert or stud, regardless" advice, but didn't I see a TSB floating around here at some point that instructed that original pistons on 2000 MY N*s be replaced with a new design or new part # in case of excessive clearance or slap?
09-09-10, 12:18 PM
I am doing the same job as you right now, but a little further along. I also noticed the same thing recently when I was cleaning the head gasket remnants from the block on my sons 1998 Eldorado. His engine has 120,000 miles on it and still had the honing marks in the cylinder bore and also had no ring ridge, I think that's amazing. I checked the gap with the feeler gauge and found it to be less than 0.010”. Back in the day when I was a drag racer I ran my 327 Chevy engines’s at 0.030”over piston clearance, they did smoke a little but there was no piston slap noise. Most likely if it ran okay before the blown head gasket as far as smoke and piston noise is concerned it will still be okay after it's put back together.
I agree that if the heads are off the block one should not put the engine back together without making the necessary proactive repairs to the head bolt threads. I feel the course threaded products are the best for repairs and longevity. My theory on this problem is that it is caused by galvanic action (Google it) that is created by two dissimilar metals in close proximity of each other. The thinner threads get eaten up quicker and fail while naturally the courser threads last longer but not forever. Remember this is just my opinion.
09-09-10, 06:19 PM
I am doing the same job as you right
Several schools of thought on the head bolt hole thread failure problem, ranging from porous block casting to corrosion by coolant to a version of your thread failure.
Where did you run the 327's ? I successfully campaigned a 1965 Chevelle 327/350 (engine(s) and suspension slightly modified :sneaky: ) at Connecticut Dragway in Willimantic back in the late 60's - while on duty at the Sub Base in Groton.
09-10-10, 10:29 AM
Pistons are not round but slightly cammed & tapered & the clearance measurement is
checked at the lowest-widest point of the skirt at north & south points on the piston .
Then the difference compared to bore ID measured at several points.
You can't judge the pistion clearance by the movement at the top.
They will float north, south. east & west in the bore at the top of the piston. Old or new.
Removing the pistons is the only way you can calculate the bore clearance.
Pistons are designed to float in the cylinder and the rings & balance help keep them square in the bore.
You will find all installed pistons will move around at the top in its range of stroke travel the bore.
As a rule pistons are smaller at the top and ring grooves areas of the upper area may very well be 0.030 smaller by design.
The north star pistons in this Picture compliments of "Popular Hot Rodding" I stole it from the website.