Coolant pressurising - head gasket leak

[gmsclassics]

Six meetings on from a total engine rebuild (new block bored out, fresh heat treated, port & polished head) I found the system pressurising (15psi on my gauge) and coolant being forced out - probably only half a litre a race.

Following pictures show what I found when taking the head off. It appears that No1 (front piston) has been blowing across the top of the gasket (Payen copper sprayed before fitting) into the large front coolant orifice in the head that feeds from the water pump. It is blanked off save for a small hole by the head gasket. It is also interesting that on the block surface, this coolant channel is closer to a bore than any other, yet it doesn't appear to be playing much part other than the small hole which I assume acts as a bleed. Note that the head has been re-torqued four times since installing.

Question is whether there is anything additional or different I can do to prevent this happening again? Is blocking off part of this hole in the block surface a possibility, or even feasible?

Otherwise I can't see that I can do anything different other than maybe re-torque more frequently. Deciding on when to do the first re-torque is problematic on a race car as first outing will be full on practice and three races, revs most of the time 4500-7000. I wonder whether I should run at 2000rpm at home until thoroughly hot, and re- torque the next day. Do that a couple of times first?

head showing evidence of leak to coolant channel

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top surface of gasket

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Lower gasket surface

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Head surface - no leak

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Maybe running a tad lean?

IMG_0392A.JPG (119.5 KiB) Viewed 1681 times

Geoff

[Dolly-Nut]

As long as you re torque after the first heat cycle you are doing your best. What are you torquing to? Should be 58lb as a minimum.

[Mad Mart]

I always get it hot then re-torque once, the next day. I then don't re-torque usually for 800-1000 miles. I torque the head to 58-60 lb ft.

[Tony Burd]

I always thought it was best to fit the gasket dry without any additional sealant or grease as the gasket itself is impregnated with some kind of sealant? That used to be the advice I followed 20 years ago but I have never built a race engine.

[Pippin]

I freely admit that I don't know too much about these things, but why is there a large hole cast in the head and a corresponding but smaller hole cast in the block, but then the water channel is almost completely blocked by the gasket when they're mated up? Is it possible that the hot coolant/pressure is damaging the gasket and making it susceptible to blowing at that point? Blowing aside, wouldn't it aid cooling to enlarge the hole in the gasket to fit the water channel?

Just my idle thoughts!

Jer

[SprintV8]

Is that a crack appearing between the exhaust valves?.

[Jon Tilson]

The porblem is surely the fire ring, not the coolant side.

Maybe the head indentations are too deep...-suggesting maybe overtightening in the past.....?

I havent changed too many head gaskets because once I've done one, they stay put.

Cleanliness, the odd blob of hylomar and clean surfaces are all Ive ever needed.

Jonners

[Carledo]

The hole in the gasket is deliberately small in the front end of the head to encourage more water to flow round the rear end, thus "evening up" the cooling of the engine. I would not open up the hole as it could lead to overheating of the rear cylinders. I'm very surprised however, that so much of the gasket has been eaten away in so short a time, i would expect the gasket to look like that after a neglected and anti-freeze free 10 years and certainly NOT after a couple of months and a few hundred miles - no matter how hard those miles were! Do you run it with antifreeze in? I know the NZ climate is nicer than ours but antifreeze also contains inhibitors to stop corrosion and should always be used in a Sprint motor, summer or winter.

Steve

[soe8m]

Copper spray is for copper gaskets. A payen doesn't need any spray. These are sprayed and a bit sticky. It does also look as if your valves are deep into the seats or it's the picture.

Jeroen

[gmsclassics]

Thanks everyone for the prompt responses. Answers:
- Just a mark on the surface between exhaust valves.
- Antifreeze was in there, good brand and right strength. Usually I just use rainwater and 'water wetter', which of course includes inhibitors. I too was surprised at the state of the gasket. I did wonder about trying to close up the hole a bit, especially in the block rather than opening up the gasket.
- Block and head were 'new' with fresh surfaces. Fire ring indentations are very superficial and cleaned up. I've checked for flatness around where the leak was and all seems okay.
- I've used 'copper spray' (see below) for many years on recommendation of someone who builds a lot of old race engines with cast blocks and alloy heads where there is likely to be considerable movement as they heat / cool, along with high compression. Not had an issue, although it is only ever a light spray.
- yes, Jeroen, the valves do look rather deep in the seats. Not noticed that before. Don't know why - guy who rebuilt, port and polished the head didn't remark on any difficulty and when I set up the clearances the shims were within normal range for this cam (STR139).

I did have to replace my torque wrench as it was reading under. I hadn't associated that with this issue as it was found when someone else checked my wheel nuts tightness and said they were not tight enough, but maybe the head was just never quite tight enough and that allowed this to start? I always torque to an indicated 60ftlb with the threads well oiled.
I have been using grade 8 bolts on place of the studs and nuts, plus capscrews in place of the shorter bolts (again for some time on the previous engine without issue) but I think I'll go back to a standard set up. I switched as last set of studs/nuts seemed soft and pulled the threads after a while - I think that was the last time I had a head gasket go. I might still use a light spray on the gasket this time....

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Geoff

[trackerjack]

Well just to add my thoughts to the wise men here.
Absolute cleanliness, I wipe the faces with brake cleaner or thinners and use the gasket neat with nowt on it. I fine spray of heated compression gas will eat gaskets fast.
When the head is skimmed dont let the engineer make it too smooth, in fact a bit rough is best.
Mart is right in as much as warm it cool and back half a turn and retorque. (One at a time)

I dont like gunning them till after a 100 or so miles and a retorque as before.

Then every now and then a retorque. Sprint heads are soft as butter and drive like a pussy till its warm then...............