Blown Head Gasket- Please Assess and Advise

houseowax · Post by **houseowax** » Sun Aug 08, 2010 9:02 pm

OK- so here's the results:
The old packings were reluctant to come up, and at several points were completely stuck against the surface to the point where they'd rip when gently pulled upon. I finally took what I could off and the remainders were heated with a heat gun until they unstuck. A brass brush and some Simple Green took care of the rest and now all mating surfaces are as clean as a whistle. It looks as if the PO used some sort of gasket sealer rather liberally- it appeared to be black and dried to the consistency of old caulk- not springy or rubbery, but pliable.
There are no scars or low points on the mating surfaces as checked with a precise Starett 8" Steel rule from a combo square. No light was visible between the head surface and the ruler. That might not be precise enough in the world of mechanics, but that's what I had.
The pistons themselves looked evenly worn and free of any scratches excepting microscopic lines in their surface. I rubbed my thumbnail over them and they were not deep enough to feel. Again, I don't know how precisely they need to be measured, but they certainly were not visibly damaged- EXCEPT: on one of the piston skirts a strange discoloration. Pic attached. Unfortunately I don't know which piston this is, an oversight on my part.
Whatever the outcome, I'm ABSOLUTELY going to need some new piston rings. The top two came off with no difficulty, but the bottom ring I broke- twice! Anybody have any advice on how to remove those- I tried to be more gentle on the second attempt, but it seems they have very little give.
The pistons, BTW, are marked 0.50, so I assume this means they're 2 over - Not standard.

teazer · Post by **teazer** » Sun Aug 08, 2010 10:50 pm

pictures can be misleading but those pistons "look" fine. the barrels look odd but that may just be the picture. Do you have a picture of the upper part of the bores and of either side of the head gasket please.

The bores should have a 45 degree (or so) cross hatch and those look like they have been bored rather than honed to size. Without good measuring tools, we have to resort to less precise means to measure.

If you insert a piston back into its bore and slide a feeler gauge between the front face of teh piston and bore, how much clearance do you get. The sides are a different shape and the tops are smaller than the bottoms, so it's only necessary to measure it at the bottom on the front or back.

Just as a point of reference, .002"is OK. .005 is a little more clearance and .010" is getting sloppy.

Rings are typically cast iron and they are quite fragile so go slowly.

gramey7 · Post by **gramey7** » Mon Aug 09, 2010 9:28 am

If I'm not mistaken, the photo of the clean piston indicates ".50", which means it's an oversize piston already so you need to get the corresponding rings if you reuse the pistons.

jensen · Post by **jensen** » Mon Aug 09, 2010 10:35 am

Hi,

According to the pictures there isn't a decent honing (cross) pattern on the cylinder wall.
This honing pattern will hold the oil so it can lubricate the piston, my advice would be bore / hone to .75 and look for some NOS .75 pistons and rings. The (upper) skirts of the piston show heavy wear too.

Maybe she runs a little rich too ?

Jensen

LOUD MOUSE · Post by **LOUD MOUSE** » Mon Aug 09, 2010 11:22 am

Just curious.
Did ya run a Flat Hone in the cylinders after ya pulled it off the pistons> ..........lm

houseowax wrote:RW, thanks for your reply. All in all it seems fairly straightforward and I feel confident that I will be able to tackle this project with minimal stress. So far I've really enjoyed it- especially as I tore down that '65 engine previously and since knew better what to expect.
I'll post pictures soon and see what you think- to my eye the pistons and cylinders looked pretty clean and free of scars or irregularities, but if I have to have the engine honed etc I can't think of anyone whom I'd trust more than LM to do the job.
Pictures and more ramblings to come.

houseowax · Post by **houseowax** » Mon Aug 09, 2010 12:09 pm

LOUD MOUSE wrote:Just curious.
Did ya run a Flat Hone in the cylinders after ya pulled it off the pistons> ..........lm

No sir- i simply split the head and cleaned everything up as best I could. They haven't left my basement and I'm not about to try anything of the sort myself!

So here's the latest:
As Teazer instructed, I inserted the piston back in the cylinder and used a feeler gauge at the front of the piston to measure the gap. I'm pleased to report that the .002 wouldn't even work it's way into the gap; if I slid it into the side wall of the cylinder and then moved it around to the front it still would only wedge itself in there rather sungly and resist when I went to pull it out.
The cylinders themselves have etchings going horizontally and vertically, but not a 45 degree crosshatch.
Also attaching a pic of the old head gasket per Teazer's request. It's pretty ragged since it was stuck pretty firmly to the cylinder head in places and it peeled apart in my effort to remove it.

houseowax · Post by **houseowax** » Mon Aug 09, 2010 12:10 pm

Pics of the head gasket after removal: