Loc: Columbia, SC
Re: Bob's 3.0L Engine
04/27/07 06:14 PM
It's good to have redone the head install - if I had not caught my error, the head gaskets may well have blown.
First, the head thickness was measured at each head bolt location:
A flat putty knife on the bottom of the head provides a stop for the depth gauge:
There is considerable variance... from 2.782"-2.812".... so 2.782" becomes the thinnest clamp area. Next, I measured each head bolt:
The range was again considerable.... 4.000"-4.030", so the bolts were all ground to 4.000". Next, each washer was measured and found to be .140" straight across:
But these are cupped washers and act as a spring that flattens at least somewhat on torquedown - the edge thickness is .130" and represents the washer thickness on complete compression:
So, the thinnest head area of 2.782" + the washer compressed thickness of .130" becomes the clamping thickness of 2.912". For now, the head gasket thickness is ignored.
Next, one of the 4.000" bolts that was not ground (longer remaining threads) is selected to try to find a deck hole where the bolt will bottom at the end of the bolt - and not bottom at the top of the bolt threads... the bolt is run into each deck hole and the highest measurement location noted. That bolt was run through a die for a 1/4 turn to see if more threaded length would allow it to go deeper into the deck (checking upper thread bind):
The bolt would not thread deeper, indicating the bottom of the shallowest deck hole was the stop. Further calculation of the clamped thickness of 2.912" plus .025" conservative allowance for compressed gasket thickness minus a generous .100" to final torque down (3/4 turn) = 2.837". To get to that exposed bolt length, it was now necessary to grind each bolt to 3.990".
Next, the deck hole with the shallowest thread step was found:
The shallowest was .170" - the dimension isn't necessary except to identify the hole location. Now, each bolt is run into that hole to check clamping range allowed by the upper limit of the bolt threads. Each bolt was run through a die far enough to allow the bolt to thread into that hole to a clamp range (as measured on the bolt) of 2.800" or less. 2.800" (exposed bolt length) minus .130" (compressed washer thickness) minus .025" (compressed head gasket thickness) = 2.645", or .137" less bolt length on full clamp than the thinnest clamp area of 2.782" on the heads and if the .100" is consumed on final torquedown, there's still .037" of room to spare. Simple, eh?
OK, I know that's convoluted as all get out - and there may be a simpler way - but that's how I entertained myself for ~5 hours until I was satisfied with the head bolts. At least now, the next mechanic can pull the heads and not worry about which bolt goes in which hole - because it doesn't matter now... unless the heads and/or deck are milled further. Any head bolt can now be used in any deck hole.
New head studs, new water pipe, distributor adapter, rear timing covers, cam sprockets, new timing belt tensioner and new spring have been installed and it now looks like this:
I keep forgetting things to order - now I need a crankshaft woodruff key before I can install the timing belt - and need the gasket for the upper radiator hose pipe flange - doesn't come in the overhaul gasket kit.
'89 G-Raider Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum
Edited by FrankR (04/27/07 09:04 PM)