Blown head gasket / causes

[TulsaSpider]

Hello all. I just returned from the Roamin Chariots MOFLO event in Osage Beach Missouri. I had a wonderful time once again. Saturday evening was hmmm... well... a tech session we'll call it. I blew the head gasket! luckily Alan had one and with the Fiat freaks there we had it off in about an hour and re-assembled and back on the road the next morning for my five hour drive home. I had maybe 20 hours on the newly rebuilt engine. My engine is a 2L block with 4.5 MM domes and 1800 head Mark's street cams. It is supposed to be about 10 to 1 comp ratio which I thought I would be fairly safe on as far a detonation goes. I had an exhaust leak for quite a while (the down pipe didn't match up after the block swap) so I had that fixed before the trip and I noticed that it was pinging under load in 4th that day. I had uses 91 octane real gas. I had the timing set at 10 degrees advanced I have a 34/36 carb. Would the jets being too small cause pinging? I got the impression that the guys who were there, thought this very well could be the culprit. I really had no idea it could cause the head gasket to blow that quickly either. The comp ring was blown out between 2 and 3 and nearly gone between 3 and 4. The guys said that one of the cam wheels could have been a tooth off. I thought I had been very thorough but it actually had more power after the procedure The ride home was uneventful, but the pinging was still there even with a bottle of octane boost. I did drive her smooth and easy for the most part but I did test for the pinging and was still present. I will get out there soon and take out the jets and post the sizes. I am pretty wiped out from the trip still...

[sptcoupe]

You probably have more than 10:1 compression, depending on what may have been done to the head (how much was taken off for rebuilds) and the deck. With some material removed, 4.5mm domes can get you into the 11:1 CR range pretty easily. That won't work with 91 octane gas.

[TulsaSpider]

I do not know what happened in the past of course but the deck was not blocked and there was nothing taken off the head on this rebuild.

[Sunracer]

I do not know what happened in the past of course but the deck was not blocked and there was nothing taken off the head on this rebuild.

did the machine shop check that it was flat? did you reuse old headbolts that may have started to stretch? Pinging when you have the time well backed off indicates a fire ring that is leaking already and causing preignition. all possibilities. PB

[TulsaSpider]

Yes surfaces were checked for flatness. Yes I did re use head bolts.

[majicwrench]

Gotta get rid of pinging. Yes, jets too lean COULD POSSIBLY contibute to pinging, but really, that aint it. You need to figure your compression, and verify TDC so you know what you are setting timing to. At the very least back timing off a few degrees and see if it helps.
Keith

[TulsaSpider]

OK the jet closest to the engine is a 140 and the one on the fender side is a 137.
I had to re adjust the timing belt and made sure the timing was a 10 btdc. Which I believe is the farthest one down. The top one, that pokes out farther is 0 correct? then 5 btdc then the bottom one is 10 btdc. The engine was really loping.. Took it for a spin and the pinging was still there. Brought it back to the shop and adjusted the timing between the 10 and the 5 mark and took it for a spin and it seems the pinging actually got worse... ugh...

[sptcoupe]

My guess is stiil that you have a very CR. It doesn't take much material removal from the head to get there with 4.5mm domes. You'll only know if you meaure the compression. If you find it is indeed the CR, you can have a thicker head gasket made that will bring it down. In fact, there may be a thicker gasket that is available from a FIAT parts supplier already. Anybody have any info on sources?

[TulsaSpider]

I am going to pull off my aluminum crank pulley just to double check that I got my timing mark right. Apparently we timed it off an errant mark this weekend and it ran better than it ever has.... now I have it timed correctly and it barely idles and runs like crap....
EDIT
I just got off the phone with Kent who put the timing belt back on. He used the screwdriver method to determine TDC because he said it seemed my mark was off. Now I am sure the mark is off so I am going to put the old pulley back on and get this correct. Grrr why can't the vendors mark their aluminum pulleys... I thought I had it right....

[maytag]

Tulsa, I'm feelin' yer pain dood. really. that sucks.

Of course there are several things that can cause the ping and the failed headgasket, but until the calcs prove otherwise, your most likely culprit is the CR. Fattening-up the jets can help, becase it cools combustion, lowering cylinder pressures. This can lead one to beleive that the ping was caused by a lean condition. not usually the case.

Figure that C/R first. there are several things you can do to help you live with a high C/R, like retarded timing, higher octane, water-injection, etc. but for a street car, none are terribly practical.

remember that C/R alone is not likely to be the ONLY factor; what is happening is that the cylinder pressure is getting high enough that some other marginal factor sets it into combustion. Typically a hot-spot on a piston, or a sharp edge on a valve that has heated-up. These things are much more difficult to control than your C/R, but it can exlain one cylinder pinging much earlier than any others, and could lead to a deeper investigation if you discover that your C/R isn't as high as we're suspicious it may be.

like I said: feelin' your pain dood. hang in there.

[Sunracer]

With the aluminum pulley you will be better of marking it on the car. Use the screw driver method. YOu will need to determine, as you watch the pulley, how much it the pulley moves at the moment that the piston dwells at TDC (top dead center) and split the difference to make the mark accurate. rotate the pulley very slightly back and forth watching where it stops moving and where it starts. This is the moment it spends at TDC, and half way between is where you set your mark. I have an aluminum pulley and this was the only way I got it marked right. Trying to line it up with the original pulley was hopeless. Concentrate on timing it by advancing it till it pings and then back off.

Once you have it running right do a compression test to see how many psi it poumps, this will give you an idea of it's dynamic compression ratio (versus mechanical compression) You might try a couple different gauges to see if you can get a better idea than just relying on one.

I know Guy Croft sells a thicker gasket, or used too, some of the other vendors, like Obert may too. I have heard of this referred to in some cases as the turbo gasket.

You will get to the bottom of it and get your motor set right. Hang in there

PB : )

[majicwrench]

The "Screwdiver Method" is a good was to get close, but impossible to get it right. Close IS NOT good enough. The piston quits moving as it nears TDC, and then afterwards a few degrees. Watching when the screwdriver starts moving is not close enough.
There are ways to get it right. Do it right. I wrote up a long description of how to do it with a simple modified spark plug, will write it up again if you can't find it.

Cranking compression really has no relationship to what is going on here. Keep it real.
Keith

[Sunracer]

Dear Majic wrench, He has an issue with pinging and how high the cranking compression is will give an idea what's going on in his engine. Since precise data doesn't seem to be available (cc'ing combustion chamber volume etc) there is little other option short of tearing down the engine and taking measurements. Not to mention if his pinging is caused by a slightly failing firing ring from one cylinder to another this may also show with a compression test, and yes I know a leak down tester would be better : ) You are very dismissive without thinking through the whole equation. If he is off a degree or two in establishing TDC to set his timing that's ok, it will give a pretty good reference to get it set very close. Take it easy, just because you are behind a keyboard is no reason to lose your manners : ) PB

[maytag]

Actually the method described by Sunracer is quite effective in determining TDC, and will have you as close as ANY factory-applied timing marks I've ever seen. You'll note, Majic, that he described splitting the moment of dwell at the top of piston travel. That IS TDC, no matter how you slice it.
Sure, I use a dial-indicator to establish that dwell. Easier... but if you're careful with the screwdriver, it accomplishes exactly the same thing.
I haven't seen your write-up on how to do it with a modified spark-plug, but I would suspect it has to do with creating a piston-stop? that's a great method too, and probably closer than I could ever get it with a dial-indicator.... but at that point we're talking a fraction of a degree at the crank... not more than that. His timing mark will likely be broad enough to encompass that difference!

[baltobernie]

Before you get the spark arriving at the right time on the crankshaft, make sure the valves are opening and closing at the correct times. If you're off a little bit, the CR can go thru the roof.

You're putting a few drops of motor oil on each head bolt before installing, right? And your torque wrench was checked against another?