72 Mercury Comet GT in Germany

found out why the first head bolt won't hold torque anymore. looks like a cracked block (lower right corner in the picture):

 

Looks like someone tried to repair it already ... doesn't it look like it has been drilled out and there is an insert there?

Sorry that it is bad news.

 

no, the metallic part you see is actually the arp bolt of which the plating has come off. i guess i now know why the bolt suddenly started leaking...

will post pictures of the cylinder walls in a minute. i'm definitely in for a new engine. i hope i can use crank and rods from this one.

 

cylinder 1:




cylinder 2:



cylinder 3:



cylinder 4:



other bank looks virtually the same.

one question i have, though. why does it look like the pistons are not centered in the cylinder bore? i have that on 7 of 8 cylinders, it's definitely not the angle of the camera:


and here's the reason i ordered a new flywheel:



as i'm not too familiar with all of this (i earn my money sitting behind a desk!), any input from a pro is appreciated.

 

Actually it does look like a larger hole was drilled in the block where the crack is and a thread saver was installed

 

the hole on the other side of the engine is just as big - aren't they that big for the dowels to go in?

 

checked some more things today. removed the oil filter. the crack runs pretty deep. so it wasn't the leaking bolt where i lost coolant, but a cracked block. wherever that came from.

removed the main caps. bearings and crank look fairly alright:












measured the crankshaft endplay, within tolerance. checked the rod side clearance, within specs.

pulled pistons 4+8. rod bearings look good, just as the mains. the pistons are heavily scratched, even right at the top.
with the pistons not centered in the bore and that kind of damage, i suspect the bore being too large or a mis-measured or -calculated piston-to-wall-clearance.

will keep you updated...
fortunately, i have a spare 91 roller block bored .030 which i'll use for the rebuild. i was able to sneak a set of srp pistons and perfect circle mahle rings into my summit order, so i will have everything here. even found an engine builder who is able to balance us v8 rotating assemblies.
all in all a major setback, but hopefully not for long...

 

today, it dawned on me what went wrong.
the block had been given to a machinist to bore it to 4.030. seems like he didn't do a proper job.
i have measured the piston while disassembling the engine - 102.24mm = 4.025" - and the bore, 0.08mm = .003" larger which results in a 4.028" bore.
i thought everything was ok, as probe specifies .003 to .007 piston to wall clearance. could this have been too tight for a forged aluminum piston?

that's why you take an engine to a machine shop, right? so they can measure and machine everything to specs... only a 4.028 bore is not exactly 4.030. bummer...

i also noticed that the pin wrist bushings show signs of wear. will need to have them replaced, too. might actually be cheaper to get new rods...

 

Everything but the crack looks normal for a engine that has been ran
Imho

 

The crack really sucks

 

i'll get some pictures of the pistons - the wear they show is everything but normal...

 

forgot to take pictures of the pistons.
read a lot about forged aluminum pistons in the meantime. it looks like my engine builder has done some miscalculations...

from what i understood, there are two types of pistons - 2618 and 4032 forged aluminum. they react differently to heat. 2618 tends to expand more.

the recommendation from probe for 2618 was .003 - .007 for the piston to wal clearance.
the new pistons, are srp. je pistons recommends a min clearance of .002 - .0025. you're supposed to add .001 - .003 for racing and nitrous and such. that makes a total of .002 - .0055, which corresponds to the recommendation probe gives for their 4032 pistons.

now back to the infamous german autobahn. would 2 hours of 100mph be considered street use or endurance racing? driving styles are very different on each side of the pond.

now i had a pretty tough decision to make. the new pistons measured 4.0275. in a 4.03 bore they would come out exactly with the recommended min clearance.
but would that give me the same catastrophic results as with the last engine?

i made my mind up and decided to add the .003 srp recommends for endurance racing. the block went back to the machinist for a final hone to 4.033. it's supposed to be ready on friday.

i'll also get back my balanced rotating assembly. as if it weren't enough, i also had to get new rods. the piston pin end bushing was seized up in one rod and had moved in two more. all bushings showed signs of wear. cheap chinese junk. should have gotten a brand name kit on the first approach. so i now have scat rods and srp piston. they're going in with mahle perfect circle rings gapped .020 top and .024 second.

hope i'll get everything right this time. if there's anything i'm missing, please chime in!

 

Why such a wide ring gap planning on a turbo or blower?

 

that's per srp recommendation for high performance street - top 4.033x.005 second 4.033x.0055.
i'll check on that again, though. nothing's filed to fit yet

 

Figred id ask i run 24/22 on mine on 20+ psi just seemed a little wide for n/a