Head skim requirement?

[MA70-3.0GT]

OK so as most people will be aware I have a confirmed BHG on my new toy. So prior to stripping I've just been reading through the TSRM to get an idea of what's required & I noticed that as well as the 58ft/lb error there is no mention of skimming of the head, only that if warpage exceeds 0.10mm or 0.0039" the head should be replaced.

I'm now somewhat confused, I was under the impression that even on a stock composite HG job the head needed skimming lightly to remove any marks left by the previous blow area.

So what I'm after knowing is, provided my head ain't cracked or banana shaped, would it need to be skimmed normally & either way what sort of service limits am I looking at for how much a GTE head can be decked before compressions are too high (and what datum do I take this from?).

I ask because the HG has been done at least once before & not many miles ago, so I'm looking for the previous mistake also & I'm wondering if maybe somehow too much material has come off the head & want to be 250% sure everything's just-so before I put the same head back on, otherwise I'll just transfer the new cams, valves & springs etc to another head & get everything right on the money.

[cre]

Just posted this in another thread... what timing...

Originally Posted by cre

Block and HG measurements are here:
http://www.supramania.com/forums/sho...sket+thickness
As you don't know what's been previously taken off the block and head your machinist will need to measure both and you'll need to select a suitable head gasket after.

[MA70-3.0GT]

Brilliant, now I've got something to go from when I finish getting the head off. Spent 3 hours on the motor yesterday, first stripping the rad & fan out (so I could do the rest standing in the resultant gap, without cricking my back!), then got everything except the valve covers, exhaust manifold & turbo off before the light went.

Today's been a total abortion due to weather so I'm gonna bone up on the best way of getting the turbo & mani' out the way before I hit it again & finally get to see the damage... (only number 6 plug was watered & I've chucked some oil down that so here's hoping...)

With a bit of luck the head'll be OK to keep a composite gasket on 'cause I don't wanna be throwing money at MHG's & ripping the block apart etc, glad I've got some actual figures to go off now so I can make a job of it.

Cheers, Dan.

[MA70-3.0GT]

Oh, one thing I did mean to mention. When I came to remove the cambelt I noticed that it's been running towards the back of the cam pulleys i.e. right on the back edge, and when I look down at the oil pump pulley it's actually been running OFF the back of this by about 1/8".

What would cause the belt to run to the back, tensioner bent? (all new kit in there from previous build) and why is the oil pump pulley not dead in line with the cam pulleys?

Also is the 7M-GTE an interference engine? (if the belt broke would I bend valves?) If not then I'll re-use the belt as it's a Gates item & has done nothing, otherwise if a breakage would wreck the valves then I probably won't risk it & pull the crank pulley off now...

Cheers, Dan.

EDIT-: So it seems there's no "magic" easy way of pulling the turbo off the manifold then, just struggle with the 4 bolts? I've got 3 of them but the lower front one is a complete PIG to get at isn't it?... Oh well, I was going to cheat & just loosen the manifold & turbo oil pipe together & tie the assembly back out the way, but the heat shield bolts on the mani' won't undo with an open ended spanner & a ring won't fit with the turbo in situ. Oh well, I'll just have to do it properly

[cre]

The 7M is a noninterference engine... no worries there. I'd replace the belt though. The drift could be due to a few things: Bad timing belt pulley (there are metal guide rings on the pulley which ensure the proper placement. The pulley isn't wide enough to maintain the belt position without them), bent cam drive gear or oil pump gear, worn oil pump drive bearings, or a bad timing belt tensioner, or even just a bad belt.

No, pulling the turbo simply sucks. Drenching the nuts and studs with PB blaster frequently over the period of a couple days often helps, but they still suck. The three nuts whic connect the elbow to the downpipe can be got by working from both the engine bay and from under the car.... I can't remember if it's both of the studes beside the engine or just one of them but one or two are best attacked from below with a wrench, a coupe LONG extensions and a helper to keep the socket on the nut from above.

[MA70-3.0GT]

Cool, I'll have a look & see if i can't find what's causing that then. Probably will change the belt, funds allowing, as now I look closer there's a bit of damage to the teeth caused by the edge of the oil pump pulley. At least if I can't afford the kit right now I don't have to worry TOO much...

I cheated a bit with the downpipe & just detached the elbow from the turbo, leaving the exhaust system complete. Also as the motor's not long rebuilt the usual siezed nuts issue was not there (helped by stainless nuts being fitted.) In the end I pulled the turbo-intercooler hose off & that gave the room I needed to get the nuts off the oil pipe.
If I can find some silicon hoses for the right money now seems the right time to do that, plus clean up the engine bay as much as possible while I can get in amongst it all. Actually it's not too bad save for the PAS fluid leaking from a hardened hose...

After all the hassle with access to turbo bolts I realised I could have left the turbo on the mani' after all, as the 7 nuts are accessible from above & without removing the heat shields! Still, I'm happy now I can give the whole lot a clean up & test the actuator properly.

So after the struggle to free the turbo, the final stripdown of manifold, cam covers & head was pure simplicity, only hindered by having to grind down an old 12mm allen key to 10mm for the head bolts. (incidentally are 10mm allen head bolts stock? I thought stock was studs/nuts from some descriptions of HG jobs, which said about removing the rear 2 studs to get the head out). Either way they were none too tight & I'm going to take the head into the shop to check warpage 'cause I don't think they were even 58lb!

So to the actual problem, you guessed it - number 6 right at the back edge... I'm not surprised these suffer airlocks looking at the design, the rearmost water jacket on the block has no corresponding channel in the head does it? And this is exactly where it blew... Come to think of it, the head to block mating area as a whole doesn't look overly well thought out to my eye. I'm talking about the intake side water jackets which are completely mismatched from head to block. What's the reason for this I wonder? If this doesn't sound right I'll be posting some pics tomorrow anyway.

The plus side of all this is I got a nice surprise when I looked at the pistons & pots, lovely cross-hatch marks still in every bore & brand spanking pistons with just the lightest coating of carbon (unsurprising considering how rich it ran when I first saw it!).

Oh and it should run & drive better than ever when it goes together again because, unlike the previous "mechanic", I will not omit to reconnect the cold start injector wire, nor the speed sensitive PAS wire!!! Some people just need their tools taken away, I'm not surprised in the least that he's been sacked from that garage!

[cre]

No, the heads do not have passages which match all of those in the block.... speculations abound concerning the reasoning from the additional jackets simply not being needed to the deletion of certain passages to reinforce the head.

Yes, stock head bolts have allen heads and no, it's not uncommon to find some which are loose.

[MA70-3.0GT]

Not uncommon to find loose bolts? Why would this be, especially after (rough estimate) 3 or 4 hours running time, if that. And would re-torquing after say 250 miles be worthwhile?

Anyway I took some pics the other night, some aren't as good as they looked on the camera but as the computer's at my folk's house I ain't going all the way home to get more!!!

First one you can just about see where the gasket's blown, although if you remember I said that bits of what looked like gasket material appeared in the top of the rad, it was & was from between the coolant passages & fire-rings on all but number 5!!!

Second to last is well out of focus but you can see the fresh hone-marks on the previously rebuilt lump & the ones either side are just to show what a sexy re-con head looks like, even if it didn't last five minutes! Head measurement by the way shows about 10 thou removed. Would this be reason enough to need a thicker metal gasket? Hope not or it's going on Ebay!!!

EDIT-: and yes, before anyone asks that workbench IS the bathroom door thrown over the top of the tub!!!

[cre]

Okay, Perhaps I should have said "not unheard of" versus "not uncommon". I had a couple that came loose VERY easily and I'm sure they weren't at the 58 they cam at from the factory. The reason for this is the same as the reason fastener manufacturers (such as ARP) say that you should retorque the bolts after a few full heat cycles... they stretch. I typically retorque twice, once after a week of use and again after a few hundred miles... it's cheap insurance.

A retorque is good practice no matter what type of fastener you use, whether bolts of studs. Manufacturers are more lax in the recommendation with studs, not because they don't stretch, but they torque more evenly (less torque is absorbed by the nut's contact patch) and they can be torqued to a higher load... nonetheless, a retorque is always good practice and I've seen enough posts by people who've found them to be significantly below what they were originally torqued to.

As for the HG thickness, what's the thickness of the HG you've got now? 10 thou is what, .0254mm, not a very big deal and by Toyota's specs acceptible. It's not going to bump the compression much at all... I'm running N/A-T, my compression is higher but safe enough. If you're planning on building things up and want to push more boost than 12psi or so I'd consider a thicker HG only so that later you've already got that part of the job done; but that's entriely dependent on your plans.

Bath tub workbench? Excellent!!!! Has it got a hose attachment too? I'd be completely down for that if I got a couple oven racks so I could spray off parts and such... my wife would kill me though... hmmmm...

[MA70-3.0GT]

Even better, I have an electric shower that actually gives HOT water (unlike most) so it's great, all I have to do is move the parts over to the sink & rinse them off! Oh and being single kinda helps things along a bit too, no woman's tying me down unless I find her doing a crank job on her Skyline or summat!!!

I'm guessing the head bolts were never re-torqued then seeing as it wasn't run much. Definitely on the list for running-in then. Unless composite HG's are available in different thicknesses I'd imagine it's stock (vernier gives it as between 1.5 & 1.08 but it's been mullered about a bit since it came off anyways). I don't think I'll be doing much tuning-wise yet so I'll stick with 1.37 for now, if i do decide to "fettle" it a bit later on I'll likely tear the whole thing down again, skim & lap both head & block and fit a MHG to be safe.

For now all I'm after is a sweet running stocker with no BHG worries so I can get on & sort any chassis/brake or other issues that pop up when I get on the road...