High comp motor requires higher head bolt torque?

[EricB]

Hey all,

Right off the bat I'll say this isn't Datsun related but maybe someone will have some wise words of advice?

So years ago I bought an ex-SCCA regional champ '73 Civic from some guy who used to race it out at Willow Springs. Same year & color as the Z & needing some assembly it was cheap and looked perfect next to the Z.

Without getting into the nitty gritty of the Honda part numbers it's a 1.2L 4cyl bored out to 1.3L using forged Venolia pistons for a 78 Goldwing (yes motorcycle!), big valve head, big cam, 4-1 header, twin 35mm Dell'Orto DHLB, etc.

After I had block honed, head re-freshed, and installed new rings/bearings I got it started. Ran fine for 3-4hrs then just quit on me without a bang or knock or anything - felt like the throttle cable had been cut... Not finding anything wrong other than the plugs looking a bit lean I pulled the head off and found a lot of coolant in #1, a little in #2, and #3/#4 looking just fine the way they are supposed to.

I haven't yet pulled pistons and rods out of the block so I don't know if one of the brand new rings just gave up (that requires first pulling axles and tranny on this little FWD which is always fun...) or if it's just the headgasket.

So with that said, & remembering how the previous owner told me his setup was good for roughly twice the power of stock (from 50 to 90ish HP), is it possible to think that the stock torque specs for the head bolts aren't enough for this little guy? BTW the setup is legit as I found old Honda racing parts brochures describing the exact same hop-up kit for competition...

What do you all think?

-e

[Bambikiller240]

Cracked block?

[Brett240]

that sounds bad Eric. i think you might be clutching for straws thinking coolant leaked into the cylinders becouse the head wasn't tight enough.

like bambikiller said could be a crack in a water gallery, maybe corrosion around the galleries in the head, a warped head etc.

how did the head gasket look? was it pinched or torn? if you pinch the gasket while torquing the head you will get a leak ( catastrophic failure time).

[EricB]

it's hard to tell what the headgasket looked like because it tore as I pulled the head off the block...

of course i'll know better once everything's disassembled I was just wondering because those 3-4 hrs were under little to no load as is customary for a brand new rebuild and the fact that i didn't hear knocking or anything else suspicious...

thanks though

[Brett240]

Eric,

what were the run in conditions? little or no load - was it in the car or did you run it in on a bench?

are you sure it didnt overheat, warping the head and letting coolant into the cylinders? brand new engines get ALOT hotter than an older engine under the same conditions

[LanceM]

Just to answer your question, head bolt torque stays the same no matter the compression. The torque amount is more a factor of the bolt than the head/block assembly.

[sblake01]

LanceM, you beat me to it.

[EricB]

It underwent the same startup procedure I was recommended here when I rebuilt the L28 in the Z. Namely: start it up, check for leaks, revs at 2-2500rpm for 10-15min, check temp, make sure fan comes on, etc. Turn off, once over including pulling the plugs. Start up again, let fully warm up, drive leisurely around the block using only minimum revs (like 1/2 the range-ish)... That's about as far as I got... & then it just stopped... I'll pull the axles this weekend and report back if I see anything obviously wrong, otherwise it's off to the machine shop for a professional opinion.

-e

[LanceM]

Before you go tearing it all apart, rings wouldn't allow antifreeze into the cylinders even if they were bad. I would clean things up, change the oil and crank it to make sure everything goes round and there are no cracks in the block that you can see in 1 or 2 cylinders. Then I would check that the head is still flat, if it is I would put it back together and run a compression check on it. If that's good then you probably just had a bad or blew a head gasket. I would say that since it just stopped and you have that much fluid in the cylinders it was a pretty catastrophic failure, not something leaking a little bit...

[JZM]

Aluminum its a funny thing. it likes to do some weird things when it gets HOT!

after you check the cylinder head for staightness/flatness you should get it pressure checked for cracks,just to be on the safe side. while taking all others advice on this subject.

JZM

[EricB]

Ok thanks guys... will do.

-e