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The mkiv Supra Owners Club

Skimming cylinder head


bigbloodyturbo
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Need a bit of advise from someone. I blew my HG last year, it started missing occasionally when still in vacuum but ran fine when on boost. Took it easy but noticed it was using coolant, problem got worse untill it really spat the dummy out one day and i had a sniff test done on the coolant, it showed hydrocarbons in the coolant. I've stripped the engine and now have a bare cylinder head on my bench. I cannot see where the gasket teared but it was starting to delaminate when i took the head off. The engine never overheated and the temp gauge never moved. I checked the head with a straight edge and toyota quote 0.1mm allowance, i could not fit a 0.1mm feeler in anywhere on the head. There was a place where i could fit a 0.05 in but toyota says this is allowable. I'm about to take it to the head shop to have it checked for hardness and was going to get it skimmed whether it needed it or not.

 

Has anyone got any advise on this? should i get it skimmed either way as i've went to all the trouble of stripping it. Are the figures in the toyota workshop manual good? Or should i just buy another head from Mr.T and be done with it?

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I'd personally run a dti or verdict clock all over the head face when its sat on a milling machine, that

will give you a much more accurate check than a straight edge and feeler gauges, the head company should

do that before they skim it.

If its within the tolerance listed then it wont do any harm to have it skimmed and wont need much taken off.

 

If it needs more than the tolerance then the heads pretty much scrap as the cam journals will be out of line by

the same amount the head face is.

Edited by Dnk (see edit history)
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Thanks for the reponses, i'm going to run it over to the Aberdeen headshop today, spoke to the guy yesterday and he said he can do a check for the hardness and skim it aswell as re-seat the valves. I'm assuming that if reconditioning heads is their bread and butter then they should be able to tell me if the head is warped and if so by how much before they machine it. I dont believe the engine has ever been stripped in its life so i believe it has never been skimmed before. I'll see what they say. Do you think i should have it faced off even if they say its in tolerance?

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I've skimmed plenty of cylinder heads and never once done this without checking it before i started, infact you should

run a clock over it to make sure its sat on the machine correctly.

 

If its in tolerance for what it costs i'd skim it but only the minimal amount off required to get a full clean up.

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I've skimmed plenty of cylinder heads and never once done this without checking it before i started, infact you should

run a clock over it to make sure its sat on the machine correctly.

 

If its in tolerance for what it costs i'd skim it but only the minimal amount off required to get a full clean up.

 

Ok, that's what i'll do then, just want to have some info for the guy when i'm talking to him. He'll do all the necessary measuring i'm sure, would like to be confident that everything is done and ok before i put it back on as the gasket set was bloody expensive.

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Just had a call from the guy working on the head. He says he's tested the hardness and its fine, he's pressure tested it and its passed and he checked the valves and they are all ok. It had a slight warp in it of 5 thou but he said that its almost negligable and doesn't carry through to the topside. Looks like its ok thank god.

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  • 1 month later...

Sorry i missed your reply, 0.005" thou is over Toyotas limit and in engineering circles

quite a lot.

 

I hope the cam journals are okay, every head i've checked when they've had a full length

warp the cam journals were out of line by pretty much the same as the head face which

isn't good at all

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are you using a steel headgasket by anychance? make sure that the block is straight and dont have any pits in it as this will make the steel gasket leak. also before doing anything to the head i would pressure test it to make sure its not leaking due to a crack or somthing.

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are you using a steel headgasket by anychance? make sure that the block is straight and dont have any pits in it as this will make the steel gasket leak. also before doing anything to the head i would pressure test it to make sure its not leaking due to a crack or somthing.

 

The op says its been pressure tested in post number 7 !

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Guest BradMD

Hi, i might need my head to be skimmed too as the head gasket has blown, question is do you have to change the stretched head bolts when you take out the head? I've found some but they're quite expensive and would prefere if i didn't have to get them.

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Guest BradMD

Well its only a minuscule amount being shaved off, so it would slightly increase the power output of the engine right? does anything else need to be adjusted tho when skimming the head?

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It theoretically will aid off boost performance, but you almost certainly won't notice any change. It will also theoretically limit how much boost you can run without hitting det.

 

It will also put the stock cam timing marks out, but unless you machine a 1/16 inch or more off the head it won't be significant.

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The stock head bolts are not torque to yield so, on a tight budget, they can be reused if undamaged. Be SURE the female splines in the heads are PERFECT. DO NOT reuse bolts that are less than so or they may well strip the splines and will need drilling out. Where will the swarf go....? :(

 

Just to add to that the manual says,

 

Using a venier caliper, measure the thread outside diameter of the bolt

Standard outside diameter: 10.8 - 11.0mm (0.425 - 0.433 in.)

Minimum outside diameter: 10.7mm (0.421 in.)

If diameter is less than minimum, replace the bolt.

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Guest BradMD
It theoretically will aid off boost performance, but you almost certainly won't notice any change. It will also theoretically limit how much boost you can run without hitting det.

 

1/16 inch or more off the head it won't be significant.

 

Do you mean cam timing marks will be fine, as well as everything else, once you DON'T skim more then 1/16 of an inch?

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