Engine Tuning problems-update
Discussion
Hi,
My last thread explained the problems I was having with my engine - not running smoothly, backfiring, metalic knocking noise, loss of power etc. I had many replies and would like to thank everyone for their input.
Over the weekend I decided to do a compression test and when all the plugs were removed I turned over the engine and out of the left bank exhaust there was a hissing sound (the right bank was silent)- not a good sign!!
I removed the fuel injection system and took off the heads. The head gasket on the left bank had a 10mm gap in between two cylinders (the source of the hissing sound). The bores seem fine as do the valves (the gasket pieces must have been blown straight out of the exhaust).
The gasket on the right bank also showed signs that it was about to break down in exactly the same place.
Any ideas on what would cause this - the car has only done 9000 miles.
Also, all cylinders were around 175psi - the 2 faulty ones had 50psi each. Is 175psi 'normal' for a 5.7 with around 450bhp?
Do you think the metalic knocking noise may be caused by this problem?
Cheers,
Martin.
My last thread explained the problems I was having with my engine - not running smoothly, backfiring, metalic knocking noise, loss of power etc. I had many replies and would like to thank everyone for their input.
Over the weekend I decided to do a compression test and when all the plugs were removed I turned over the engine and out of the left bank exhaust there was a hissing sound (the right bank was silent)- not a good sign!!
I removed the fuel injection system and took off the heads. The head gasket on the left bank had a 10mm gap in between two cylinders (the source of the hissing sound). The bores seem fine as do the valves (the gasket pieces must have been blown straight out of the exhaust).
The gasket on the right bank also showed signs that it was about to break down in exactly the same place.
Any ideas on what would cause this - the car has only done 9000 miles.
Also, all cylinders were around 175psi - the 2 faulty ones had 50psi each. Is 175psi 'normal' for a 5.7 with around 450bhp?
Do you think the metalic knocking noise may be caused by this problem?
Cheers,
Martin.
Is it the back set of pistons? It could have run lean and detonated/overheated. Uppping the fuel pressure and running a wide band o2 sensor with mapping abillity is what I would do. The problem now is did the piston overheat and shrink? The skirts tend to collapse and lose there original shape once they have experienced overheating, hence the slapping mettalic sound. You already have the heads off, I would drop the oil pan and mic the cylinders/pistons also. If you have stock pistons Just throw a new set in there for insurance, they where running under 200.00 for pistons, rings and rod bearings. Even if you see no gauling on the cylinders the skirt may have still collapsed. I just went through this on a Sbc v6. Had a mettalic slapping sound tat tat tat which would come on after letting up on the gas. It had blown headgaskets originally my freind had figured he could just re ring the pistons and put new headgaskets. He figured wrong. So he had to buy a new set of pistons and I helped him install them. Noise is gone, this car had seen over revs and floated the valve train causing a lean out condition.
Wow! Yes, check for warping. Was the blow-out near a water jacket? Check for water in your oil...and oil in your water. Did any of the head bolts appear loose when you removed them? Where, exactly, was the blow out? Did you have overheating problems?
What material(s) was the gasket composed of? Get the best replacement you can find. I would definitely check with your engine builder and find out what gasket he used. See if he has a build sheet for your engine (and get a copy). Not by much, but gasket thickness will effect compression ratio. Be sure to keep the old gasket for reference, if you can't find out what originally was used.
Some would reuse the head bolts. It's just me, but I would not...maybe, if I had bought them just before this installation and torqued only once and properly. As you probably know, improper torque can cause gasket/warping problems. You might even measure the lengths looking for perminent stretch. If you are going to use motor oil as lube when replacing the head bolts, be sure to put some under the head of the bolt. The idea is to reduce friction to get accurate torque. Also, be sure NOT to drip any oil INTO the holes. Blow the bolt-holes out well and just coat the threads on the bolt enough to make them shine.
Worst-case would be the block surfaces are warped.
Yes, the knocking noise could have been the compression leak.
Checking on some other ideas and will follow up...
What material(s) was the gasket composed of? Get the best replacement you can find. I would definitely check with your engine builder and find out what gasket he used. See if he has a build sheet for your engine (and get a copy). Not by much, but gasket thickness will effect compression ratio. Be sure to keep the old gasket for reference, if you can't find out what originally was used.
Some would reuse the head bolts. It's just me, but I would not...maybe, if I had bought them just before this installation and torqued only once and properly. As you probably know, improper torque can cause gasket/warping problems. You might even measure the lengths looking for perminent stretch. If you are going to use motor oil as lube when replacing the head bolts, be sure to put some under the head of the bolt. The idea is to reduce friction to get accurate torque. Also, be sure NOT to drip any oil INTO the holes. Blow the bolt-holes out well and just coat the threads on the bolt enough to make them shine.
Worst-case would be the block surfaces are warped.
Yes, the knocking noise could have been the compression leak.
Checking on some other ideas and will follow up...
Edited by builder on Monday 26th June 17:06
Just to answer your question 175 is normal in a 9.2 compression ratio engine This is with the throttle open. Overheating in the back of the block is the likely cause. I installed a Edelbrock performer Rpm Airgap manifold which has water jacket bosses on the back which allows water to crossover. I crossed it from left to right and then ran a t-fitting to the front boss on the manifold which allows the whole system to bleed the air out of it and also allows circulation from the back of the block to travel to the front and straight to the radiator. I never overheat or have any problems with head gaskets. I always use the head bolts over again on early model sbc unless I see somthing wrong with them. Good point on blowing out the head bolt holes, I have seen many rebuilds go bad becuase of this not being done. I love what I do...
If the heads are warped, a tech friend said strip the heads and have them milled 0.010". Replace the gasket with a FelPro. Ask an engine builder, but I would think you will need/want a thicker gasket than the original to offset any milling so as not to change your compression ratio.
Maybe someone will suggest otherwise. But, if you go this route, my guess is that you will want to "clock" the valves when you take them out so you can put them back in the same spot (cylinder and orientation). A cardboard box with holes cut in it for the valve stems works well for this.
Before removing each valve, mark it with the cylinder number and draw a couple of lines with a perminent pen across the edges of the valve and onto the combustion chamber. Then, you should be able to line them back up for re-assembly. Maybe protect the ink marks on the chamber with some painter's tape for easy removal. Pop the valve stems into the box for easy identification on re-assembly.
Clocking might be overkill, but again, that's just me. I don't think I would clock the springs, but I would put them (and the retainers) back on the same valves.
Maybe someone will suggest otherwise. But, if you go this route, my guess is that you will want to "clock" the valves when you take them out so you can put them back in the same spot (cylinder and orientation). A cardboard box with holes cut in it for the valve stems works well for this.
Before removing each valve, mark it with the cylinder number and draw a couple of lines with a perminent pen across the edges of the valve and onto the combustion chamber. Then, you should be able to line them back up for re-assembly. Maybe protect the ink marks on the chamber with some painter's tape for easy removal. Pop the valve stems into the box for easy identification on re-assembly.
Clocking might be overkill, but again, that's just me. I don't think I would clock the springs, but I would put them (and the retainers) back on the same valves.
I agree that the valves should be put back in the possition from which they originate, but surely once in operation they will rotate on the seat so why be so critical when installing them with regards to indexing?If it where me,I would clean the valves and seats and lap them before re-assembley (de-coke).
Edited by GTWayne on Tuesday 27th June 08:14
GTWayne said:
I agree that the valves should be put back in the possition from which they originate, but surely once in operation they will rotate on the seat so why be so critical when installing them with regards to indexing?If it where me,I would clean the valves and seats and lap them before re-assembley (de-coke).
That's a good idea...to have them cleaned up since they are out anyway. Good opportunity. Indexing is probably not be necessary, but I do totally excessive things sometimes just to go one step beyond. Like I said above, that's just me...and don't call me Shirley.
Here's an informative post about head gasket failure.
Detonation is the cause of the head gasket failure you described.
A vacuum leak will cause a lean condition and detonation, also too much timing, or too low octane fuel. A rattling sound is an indication.
Use Cometic or FelPro multi layer steel gaskets, much better than fel-pro blue. You may want to check the bearings as detonation will wear them out in a heartbeat.
Jeff S
www.schwartzperformance.com
A vacuum leak will cause a lean condition and detonation, also too much timing, or too low octane fuel. A rattling sound is an indication.
Use Cometic or FelPro multi layer steel gaskets, much better than fel-pro blue. You may want to check the bearings as detonation will wear them out in a heartbeat.
Jeff S
www.schwartzperformance.com
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