Getting ready to put a Toyota 7MGE engine together. A family member insists the head bolts should be lubed before torquing. Agree or no? If so, what's the lube of choice? Also, is thread sealer neccessary for this engine? Do the head bolt threads encounter the water jacket at all?
All books call for dry torque unless otherwise specifically stated.
The torque difference between wet and dry can be up to 60% easy I believe.
No engine I have ever owned called for lube.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile... Canadian Off Road Trips Photos: Non members can still view! Jan/06
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To quote the factory procedure: " Apply a light coating of oil to threads and underside of cylinder heat bolts." This is pretty much standard procedure because lubricated threads have a far more predictable coefficient of friction than dry. I can't at this time think of any engine that calls for installing the head bolts dry, but there may well be. If the bolts go into water passages case sealer is essential. The sealer is a half-assed lubricant. An example would be the ubiquitous Chevy small block. For a couple random samples I looked up a 92 Honda Civic and they called for lubing the head bolt threads but NOT the bolt heads or washers (???). A 4.6 Ford V8 called for lubing the bolt heads but not the threads. I think the mandatory new head bolts come with the threads coated in this case which is common.
I've seen some shop manuals direct you to dip the bolts in engine oil before installing, but I'd certainly believe that some spec it one way and some another. The last engine I actually put together was a Studebaker V-8 though so I wouldn't hazard a guess what standard modern practice is. I'd defer to the FSM, unless you are using aftermarket fasteners like ARP, in which case I'd follow their instructions.
FWIW, ARP fasteners, or at least ARP's VW rod bolts, *are* torqued with lube.
My factory manual for that car calls for engine oil on the head bolt threads and the "washer contact surface" (yes, singular).
Previous models' factory manuals I have call for you to "apply engine oil to the cylinder head bolts and the washers", without specifying surfaces.
Honda is also very particular about crankshaft bolt lubrication, stating that you should lube the crank bolt threads, but not the part of the bolt that contacts the washer.
I love Honda. Not as weird as Citroen, but getting there...
curious - on my race car (sbc) we just use engine oil on all the head bolts - never had any leaks, but always wondered if I should be using sealer instead. Depending which manual and which mechanic I talk to, I get slightly different answers, but all sbc manuals I've seen specify engine oil and/or sealer on the head bolts.
Generally, bolts should be torqued clean and dry unless otherwise specified. The use of a lubricant can give a wide range of applied torque variation depending on the lubricant used. Plain old engine oil can reduce perceived torque by
30%. Because of the multiplication effect of the thread pitch, the clamping force and tension on the bolt or stud can be several times the correct load. Therefore, engineers prefer to specify torque for clean dry threads because it is predictable and consistant. If the fastener is plated, the specified torque will only be good for that surface treatment.
Sorry, I do not know if your interface with the water jacket. Most head bolts are installed into blind drillings.
We used to use Loctite stud & bearing mount to secure the head bolts into the block on the old air cooled VW's (1960's) cylinder jugs. Used a more removeable loctite to secure the heads to the bolts. Never had one loosen up.
NOTE: This TSRM calls for 58 Ft Lbs of torque. Most people rebuilding/replacing the head gasket say to torque to 72 Ft Lbs.
If you joined the SOGI/ snipped-for-privacy@supra.com group like I suggested when you started this project, bounce a message off them and ask them. There is a LOT of knowledge on the 7M-GE there!
We went through this on this newsgroup a year or two ago and the received wisdom for American cars of previous years were that many specified torque values with clean and dry threads.
Some of us like to have a little antiseize in certain applications, such as lugbolts for example. I researched the web at that time and found that the results vary somewhat, but in general a lubricated thread (and antiseize does have some lubricant properties, as does engine oil, moly grease, etc). required about
15-25% less torque to achieve the same clamping tension as a dry threaded torque sequence. (Memory...hope it is not too far off;>)
Some GM bolts do go right through or into the water jacket. I was always told that a little non hardening sealer around these might be a good idea. The Ford engines I used to race went into blind bores, AFAIR.
This doesn't make sense to me. Although I'm far from super-experienced, my experience tells me that there's at least one variable involved here, and that's the condition of the threads. I'd bet a shiny donut that a cold-rolled bolt into a hole tapped by a dull factory tap would take more torque than a freshly-cut bolt run through a die would when put into a freshly-tapped hole. Seems to me the engineers would want to do away with a lot of that variability by lubing the threads. But that's just my uneducated, empirical observation.
Not to say that you're wrong, or even that you're at fault in any way, just that it doesn't make sense to me.
Technically you are supposed to use new bolts on heads usually....
Old bolts do have a different torque usually. When they give a torque range, I always go to the higher torque on old bolts and the lower on new ones.
Dry still keeps the variables down.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile... Canadian Off Road Trips Photos: Non members can still view! Jan/06
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(More Off Road album links at bottom of the view page)
Of course, the thread condition on both the bolt and the bore have a contributory effect.
In those earlier situations, we were always supposed to chase the bore threads with a tap (usually a bottoming tap). And, we normally cleaned the head bolt threads with a wire brush on a grinder, or somesuch. You could also run the headbolt through a die.
If a headbolt stretched, then it should be replaced. Otherwise, if it were within the elastic limit, no problem.
Some years ago, new head bolts were NOT necessarily specified. Now, some are, especially if you have a torque/index situation.
The main thing is, IMHO, to know what is specified for your particular engine, and to follow those specs as reasonably as possible.
For example, if your headbolt torque specification is 140 lb-ft, dry threads, then I dont see that you have to worry if you are at 138 lb-ft or 144 lb -ft. That is close enough.
You want clamping force. That is the whole issue. You measure this parametrically (and perhaps erroneously) by torque. Perhaps the only way to know this with good accuracy is to use a bolt elongation gauge.
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