head gasket failure- something sinister or just 7M?

[RyleyMA61]

okie dokie

i wish to hear opinions as to why my headgasket failed- just in case i need to upgrade the cooling system further.

im not looking for "because it's a 7M" answers, so please don't tell me so, more "is there anything else fucked"

it appears that the copper 'bridge' between the coolant gallery is bubbled and deformed. it is the worst on the gasket at cyl 6 and best at cylinder 1, and every cylinder in between shows a sign on it in graduated steps of "badness" from 1 to 6.

is this due to the cooling system being less efficient towards the rear of the block (with the 7M in the MA61), and thus causing deformation in the gallery and into the bore?



more cylinder 6


headgasket


or, did it start the other way out? (ie, bore to cylinder)

the reason i ask is there is no damage or deformation to the cylinder ring at all. the gasket has corroded around it.

the 7M has a standard gasket torqued to 72 ft/lbs and new head bolts, running 13psi. was good as gold for 3 years, including 2 track days. finally went boom at a track day over 200kmh. no thermo fans, flushed out radiator. undertray and top air diversion plate.

a month or so before the track day the bubbles into the overflow just started happening.

any opinions as to what caused the gasket so i can rectify any inefficiences with the cooling system would be great. i have twin AU thermos on the way, but don't want to rebuild the motor if the cooling system is the reason for popping gaskets. hopefully someone can shed some light.

thanks!

[thechuckster]

compare block with head - is the copper bridge compressed by both?

From memory, the 5me HG's that water-jacket channels in the block are not mirrored in the head. And my HG had failed around that bridge and encouraged some corrosion in the head from that point in towards the fire ring.

[woggin]

less water pressure at the back of the block possibly, causing water to stagnat (or spend longer in the area), heating up and deforming the copper, dirty galleries, air pockets? blocked galleries??

im no professional, in fact i have never even worked on a 7m, but yea, there are some ideas!!

(ahhh, dont beat me)

wog

[cambelt]

Looks like the results of a bit of detonation between cylinders at 5 and 6 but if the head came loose it would start to blow anywhere there is less sealing/ tension .
If you never retorqed it after doing the gasket that is prob the main reason yr gasket went. In 100000 klm you must retension it a few times if it's driven hard.
Dave

[madmont]

If the aluminium head has gone soft from overheating it will not hold the gasket properly. Check the hardness and if soft throw out.

[RyleyMA61]

thanks guys.

am going to get the head hardness tested very shortly. the motor would have been lucky to have done 10,000km on that gasket...

but thanks for that, prtty much reassuring my hunches, appreciated!

getting everything done/tested/checked etc soon

[JZA70R_92]

Would is a good way to improve cooling at the back of the head area??

[RyleyMA61]

i may be looking into a higher-flowing water pump impellar wheel. haven't given it much thought yet so mightn't be feasible but will let you know

[mark_vdh]

I remember a topic on the supraforums about drilling a water passage near the back on the the head
not sure what the final conclusion was, can't find the topic sorry
any one know anything about that?

[andrew_mx83]

i read that too. there is some phantom hole in the 7m head that needs to be drilled out to "solve" the HG issue.

[cambelt]

Ive drilled the hole on a few 7M,s but i cant give any results as all of them are still in trouble free service .
Dave

[rob]

thanks guys.

am going to get the head hardness tested very shortly. the motor would have been lucky to have done 10,000km on that gasket...

when the head was initially torqued did u re-torque it after 1000kms?

[TheStitt]

Ive drilled the hole on a few 7M,s but i cant give any results as all of them are still in trouble free service .
Dave

i've never heard of this and would be interested to hear more

another theory I have heard is that the if the heater tap is shut hot water builds up behind the heater tap and back towards the head, thus creating a hot spot at the back of the head

[boxh34d]

Also interested in the drilling idea.
Spill the beans dave!

[RyleyMA61]

head was retorqued after 500kms with no boost, and again 500kms with minimal boost

the guys redoing my head and block had a look, said it looked a lot like fretting....

interesting!

[mark_vdh]

pretty sure the topic was on http://www.supramania.com/forums/
but I'm not a member and can't search

found this on the cressida forums tho
http://forums.toyotacressida.net/for...r+passage+head

[cambelt]

Yep thats it , I originally did it because id see corosion at that spot that wasnt drilled , the air formed a little pocket that had knowhere to go.
7M,s have terible water flow and must be improved for better cooling .
All the earlyer M engines had much better water pumps on them and flowed so much more water than a 7M one .
A way i improve a 7M pump is machine the step off, around the outer of the pump bringing the impeller closer to the housing.
They really need a 8 vane impeller like a 5M.
Dave

[allencr]

head was retorqued after 500kms with no boost, and again 500kms with minimal boost
fretting....

I think it should be a regular maintenance item, especially if these 500kms increments were during a break-in that was babied & never once got even close to stinking hot.
The after-market gasket might be an exact copy of the original factory gasket but the factory may have 1 or more newer/improved(?) versions to replace it, with strengthening or progressive coolant passages, materials, whatever.
The water-pump would help at idle, but I'd go for opening up the passages towards the rear, or even just keeping a high idle for faster flow to equalize things after hard use. Short term hard use probably won't heat up that intake side like a 4000-rpm for an hour on the highway run will.

[JZA70R_92]

will a 5M pump fit on a 7M though? Mines only NA but I like to improves its durabilty!