From digest.v4.n725 Thu Jun 13 10:37:35 1996
From: gunnar_elmgren_at_se.ibm.com
Date: Thu, 13 Jun 1996 10:31:42 EDT
Subject: M20 Cylinder head bolts--horror strory (revisited)

Hello all,
saw a thread on replacing the 'old style' Hex head cylinder head bolts on the M20 (small six). I am glad to see that people do the swap BEFORE the bolt heads snap off (which they WILL do , eventually). I didn't, which i deeply regret right now. Abbreviated story:

• - Father-in-Laws '87 320i lost coolant a while ago. Got some help by various digest members to find where the coolant went (thanks Oleg!). I found it in the oil sump, well mixed with the engine oil to an undescribable, whitish 'goo'.
• - When the valve cover came off, a 'snapped' head bolt on the intake side between cyl 5 and 6 was discovered. Coolant came up along the bolt. Could not detect any damage caused by 'bouncing' bolt head. (Bolt head was found resting in what appeared to be a safe place).
• - Removed cylinder head, and inpected for damage or 'warpage'. Seemed OK, refitted with new head gasket and bolts.
• - Car ran fine, did'nt seem to loose any coolant until last week when i drove it myself for a couple of days. Suddenly, the coolant level check light came on, and indeed, coolant was missing....
• - Found coolant in oil sump again. Valve cover off, all head bolts (new 'TORX' style, of course) were intact. Applied air pressure to the expansion tank. Coolant sprayed out from underneath the camshaft above cyl A6.
• - Removed cylinder head again, and took it apart (rockers/shafts plus camshaft out). Found the REAL reason for leak: The 'snapped' bolt head had travelled underneath the camshaft. A6 exhaust camlobe 'punched' the loose bolt head against the cast aluminum, and produced a halfcircle crack, 1,5 inch across, into the coolant passage. There is also a very nice, hex shaped 'tattoo'. Cam lobe slightly injured, too.

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  I guess the message is, REPLACE OLD STYLE 'HEX' CYLINDER HEAD BOLTS before they break! The potential problem affects every 'small six' (M20) built before '89 or whenever the 'TORX' bolts were introduced. The type of bolts can be identified even without lifting the valve cover. Remove oil filler cap, use a flashlight and look at the bolt heads. The torx style have 'splines' on the bolt head, the old 'dangerous' bolts have conventional, 19mm hex heads. Torx bolt kit + instructions should be available at your nearest BMW dealer, to a decent price (MUCH less than fixing a cracked head....).

What happens with our cracked cylinder head? Well, for the moment it is with a machinery workshop, that claim they can weld the crack. (The guy has built the engines for the Mazda Europe Rally Team, so i guess he has some credibility.) If any of you digesters have an opinion about such welding tricks, please post it or E-mail me. The camshaft probably has to go also, and a Shrick 284 degree piece is cheaper than the stock BMW part..... maybe combined with a new DME chip..???

Thanks for the bandwidht, and please replace your head bolts!

Gunnar Elmgren
Stockholm, Sweden
'71 1600-2 Vollcabrio
'75 2002tii
'88 735iA (Der Panzerkreuzer, still for sale, has to make room for M5)

'87 320i (Father-in-Laws, momentarily headless)

Gunnar Elmgren
AS/400 Software Support, IBM Sweden