Why did my HG just randomly blow...?

[Dj Buttchug]

Stock m42
19lb mustang injectors
Cold air intake
Very well maintained ect.
178k miles.
Perfect cooling system
Never overheated since Ive owned it...

What could cause this?

Note: lean conditions of cyl 1 on the left are likely from the Hg having a small crack at the point of failure for quite some time. I experienced a subtle pinging noise/ knocking for about 60 miles before it grenaded.

Thoughts?

[Exodus_2pt0]

178k miles. These thing's DO happen to stock motors from time to time.

[Dj Buttchug]

178k miles. These thing's DO happen to stock motors from time to time.

this is the only thing I can think of. Just simple gasket failure.

[roguetoaster]

Isn't the failure of the surround rings generally caused by detonation?

[wazzu70]

I think the pinging/knocking noise you heard for about 60 miles was the issue. Detonation usually blows the gasket like that, and sounds like you had some.

Not sure why you would have the issue. Timing reference may have been off, or something of that nature.

[d_elson0]

Or crappy gas possibly will cause detonations. Don't know much about m42 but was common with subaru fools not knowing the turbo cars require 91.

[wazzu70]

I was thinking that as well. Maybe a tank of really crappy gas.

Even with a stock chip/stock timing it could cause your issue.

[Dj Buttchug]

Or crappy gas possibly will cause detonations. Don't know much about m42 but was common with subaru fools not knowing the turbo cars require 91.

this is a NA car.

I was thinking that as well. Maybe a tank of really crappy gas.

Even with a stock chip/stock timing it could cause your issue.

I only run shell or chevron 91 fuel. Never had any detonation issues. If detonation was in fact the issue wouldnt I see signs across all cylinders?


The only other reason for failure could be injector #1. They are mustang injectors pulled from a yard with unknown mileage. Its possible that one injector could be malfunctioning causing a lean condition

But even that doesnt add up. The car ran to well before hand.

[Dj Buttchug]

so just to update I found out why my problems occurred. Somewhere in the history of this engine someone decided to cut the head with the valve train still installed in the head... WTF???
So I had to shave 10 thousandths of an inch off to make the head straight. Huge douches.

Because of the excessive removal of material I couldnt run a stock HG anymore. The timing would be all jacked and the valves would probably hit the pistons even when correctly timed. Assuming previous owners cut off more material before me I decided to go with a .098 MLS hg to compensate for the loss.

for reference the thickness of a stock HG m42 is .070 respectively.

Anyways. After two weeks of waiting, a wrongfully sent s14 MLS gasket from VAC motorsports and other issues, my beast is back and better than ever.

[bmwman91]

Big bummer buttchug. Glad you root caused it though. Peace of mind is always nice.

Which 19# injectors are you running. The M42 stockers are ~21#, so using 19# ones will lean you out. The M42 already runs a tad lean in the 2500-4000RPM range at WOT.

I wouldn't worry about the timing change due to the shaved head. That's what adjustable sprockets are for! Just get the crank and cams at TDC and bolt the sprockets into place. I suppose that it is a non-issue with the thicker gasket though.

[Dj Buttchug]

Big bummer buttchug. Glad you root caused it though. Peace of mind is always nice.

Which 19# injectors are you running. The M42 stockers are ~21#, so using 19# ones will lean you out. The M42 already runs a tad lean in the 2500-4000RPM range at WOT.

I wouldn't worry about the timing change due to the shaved head. That's what adjustable sprockets are for! Just get the crank and cams at TDC and bolt the sprockets into place. I suppose that it is a non-issue with the thicker gasket though.

right. it is indeed not an issues with a thicker hg. Im running the 19 mustangs so I am a bit leaner than stock. I may get a wideband in this thing just cause. After all a lean conditions was not the cause of my failure. It was the head surface being so far out of spec the gasket could not seal properly and eventually burned out across cylinders.
In between cylinders was the worst part. They were all 6 7 and 9 thousandths out across all 4 at this location. It was just a ticking time bomb created by whoever did top end work before i owned the drivetrain.

[Balleristic31]

Wait mustang injectors flow less than stock? I'm confused. Stock injectors are 19# no??

[decay]

Wait mustang injectors flow less than stock? I'm confused. Stock injectors are 19# no??

that's always been my understanding-

realoem reports BMW PN 13641466116 which is Bosch PN 0 280 150 714

reported here: http://www.injectorrx.com/bosch-fuel-injectors/ as 192cc/min

[bmwman91]

The flow values you get online for Bosch injectors can really vary. In many cases, they are flow values that so and so's shop measured. Many times they don't report the pressure that they measured at, too.

I found what looked like an official Bosch spreadsheet once, and it had our 714's listed at 214 cc/minute, which is 20.9 lb/hour.

[decay]

The flow values you get online for Bosch injectors can really vary. In many cases, they are flow values that so and so's shop measured. Many times they don't report the pressure that they measured at, too.

I found what looked like an official Bosch spreadsheet once, and it had our 714's listed at 214 cc/minute, which is 20.9 lb/hour.

interesting. explains why i still needed a bump in rail pressure after going to 24lb/hr. thanks.