Quote:
Originally Posted by Killa B
" The cause for this is inferior quality OEM cylinder head bolts. The factory Toyota bolts do not provide enough clamping force to keep the cylinder head tightly clamped against the block so, over time, the bolts stretch and the head gasket blows out."
I am LITERALLY quoting what jscspeed.com says at the top of the ARP headbolt page
http://www.jscspeed.com/catalog/ARP_...bo-6902-1.html
Is this ACTUALLY true or are they just trying to wean me over into spending more money on ARP Head bolts?
NOTE: My car is a NON TURBO. i do realize this application is only for the 7mgte |
That's a complete crock of shit. I've measured 20 year old stockers which had been reused and even over torqued and there was absolutely no sign of pitting or torsional distress. The stock head bolts were installed at 2/3 of their rated, optimum torque (per multiple industrial standards) and generally lasted well over 100K miles... The fact that you see a lot of them fail now isn't surprising in the least... but it's not the fasteners at all. If fasteners don't measure within spec, are pitted or flaking then the must be disregarded but otherwise they are reusable (by design).
Cleaning the thread bores with a wire brush is NOT the same a chasing and chasing must be done for proper torque to be achieved.... It's well known amongst engine builders, general mechanics, machinists and engineers but Toyota was even gracious enough to put it in the TSRM too.
If you had both block and head cut then it's unlikely that the issue is that they weren't flat... at least not flat enough for a composite HG. For one reason or another a coolant jacket AND a bore jacket are not sealing... This is a bit much for a defect to be the culprit. I think that you're most likely dealing with a head that isn't all the way down. There are a couple reasons this could happen; The most common is that the lower, rear timing plate which bolts to the block was not attached to the block when it was machined. These need to be together when machined ad the HG and head lie on top of BOTH. If the timing plate isn't cut the head sits high there, you loose oil out the sides at the very front (how soon this starts happening depends on the offset) and you get coolant passages that are open enough to expel coolant and allow combustion gases in. If the timing plate is cut more than the block you'll find oil leaking into the timing belt area. Also, if you forgot to put the RTV in the specified locations before placing the HG on top of the block you'll get an oil leak out the front sides too.
HG dressing is helpful, especially with older engines.. it's not a must have and with most MHGs it's generally a no-no. I use it on regular paper gaskets and on composite gaskets, The only dressings I use are made by Hylomar but they seem to be getting hard to find around here these days. They are a high heat tolerant adhesive which never solidifies/dries. Permatex copper is what you'll find in a lot of DIY garages though and it's decent enough... just don't use it on anything with a Viton seal. If in doubt look for one that's solvent free.
Composite HGs are decent for even mildly upgraded GTE setups. The head gasket wasn't even the problem with regard to the blowing... not really. MHGs are preferred as they are MUCH more rigid and can tolerate a LOT more abuse... but a thoroughly rebuilt 7M-GTE can take more than a CT-26 can dish out on a stock HG without significant concern provided that everything else has been well planned out too.
ARP bolts are cheap but I really do think of them as interchangeable with Toyota's (Toyota's, not generic). If you feel you need to upgrade your fasteners my only recommendation these days would be going to studs... They're capable of a higher clamping force and you won't find yourself worrying about uneven torque due to a malformed thread in the block creating friction. You just screw the studs in until they're all level and the you torque the nuts down on top.
One other thing to note is that torque specs vary depending on what lubricant was used. I think I posted a table covering a number of fastener sizes and the torque required for various lubricants... can't remember... I might have just found a website with it and posted a link. Anyway, you really only want to use a high molybdenum content grease (aka moly grease).... A dense PTFE (Telfon) grease will work too but I've never tried it for this application so don't consider this a recommendation. The spec of 75ft lbs for head bolts is based on the assumption of well formed (thoroughly chased) threads and a lubricant with a friction coefficient of approx .10 to .12 (such as moly grease). If using a 30wt oil (another common practice but accuracy if reduced) the torque required for the same clamping load goes all the way up to 90ft lbs. ARP sells an assembly lube with a guaranteed friction coefficient... You may use it anywhere on the engine and you'll get far more accurate torque readings. The reason I mention this is that not all lubes are made the same and even the same brand motor oil may have a subtle shift which is really BIG for these types of application.
Had enough? I'm literally falling asleep at the keyboard (no literally, took sleep aids and THEN started this post.... durr.) so I REFUSE to take any blame for any errors or omissions..... I'll fix 'em if I see any tomorrow. G'night and good luck!