johnc Posted May 7, 2012 Share Posted May 7, 2012 Engine builder says this was caused by a lean mixture. There are no other signs of detonation or leanness so I was wondering if anyone else has seen something like this? Engine was rebuilt and then broken in on the street for 100 miles before 40 laps on a race track. Head gasket let go at the end of the day. Thanks for the help. Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 8, 2012 Share Posted May 8, 2012 Chech for block or head irregularities in the area. Even a 0.002" "wave" in the surface (cumulative-0.001" on the head, 0.001" on the block) can alter clamping forces enough to make it susceptible to blowout when you hit some in audible detonation. I had an Isuzu/Chevy Luv that repeatedly blew head gaskets in the same spot. Instead of decking the block (which had what looked like a "rusty spot " there, at the recommendation of a former Isuzu Engineer I placed a triangular piece of stainless steel shim stock on the area with red RTV and damned if it didn't stop the issue. He said in some cases 0.001" shim would be used instead of milling the surfaces and screwing to the blueprinted centrelines... Quote Link to comment Share on other sites More sharing options...
madkaw Posted May 8, 2012 Share Posted May 8, 2012 Is that a Nismo Gasket? Quote Link to comment Share on other sites More sharing options...
johnc Posted May 8, 2012 Author Share Posted May 8, 2012 No, most likely FelPro. Quote Link to comment Share on other sites More sharing options...
ozconnection Posted May 11, 2012 Share Posted May 11, 2012 Has the engine overheated once too often in a previous vehicle and the head has gone soft? Quote Link to comment Share on other sites More sharing options...
johnc Posted May 11, 2012 Author Share Posted May 11, 2012 Engine has not been overheated since the current owner has had it. Was bought as a "rebuilt" engine off the internet, ran about 6 months, and then number six rod bearing failed due to assembly and oiling problems. Engine was rebuilt and the failure above occurred after about 4 hours of total operation. Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 11, 2012 Share Posted May 11, 2012 (edited) And the deck/head check in the area of failure revealed... I don't even want to guess where the Internet rebuild came from... Edited May 11, 2012 by Tony D Quote Link to comment Share on other sites More sharing options...
MadMaxDallas Posted May 12, 2012 Share Posted May 12, 2012 (edited) I have just experienced the same, see my gasket. I took the head in and had it checked. They said it was flat and ok. I used a feltpro gasket too. I feel it might have been lean too. I had put 441 injectors in and adjusted the afm to compensate but did not use a wide band sensor and display. I am going back to original injectors and settings till I get a wide band to get it set right. On a side note, I also found a bit of flashing in the water gallery, thought it was a leaf, that may have helped make 5&6 hotter. Since these are the problem areas anyways. Also noted this time I ordered a different feltpro gasket, the holes were different we will see if it any difference. Maybe somehow I got a na gasket before? Did not know there were any differences. But what I noted is the water pass through holes around 3&4 were blocked on the new gasket. Which would probably force the water further down towards 5&6 before returning. Edited May 12, 2012 by MadMaxDallas Quote Link to comment Share on other sites More sharing options...
Gollum Posted May 15, 2012 Share Posted May 15, 2012 Why does the builder assume a lean condition? Could just as easily been a hot cylinder from cooling inconsistencies right? A cylinder doesn't have to be in a "lean range" to detonate per say, that's all. Quote Link to comment Share on other sites More sharing options...
z-ya Posted May 15, 2012 Share Posted May 15, 2012 John, What is the CR? What gas are you running? How much total advance? We had a problem on our last race engine where detonation was causing the gasket to blow out the side of the block on the passenger side, between 4 and 5. Switched to a 50/50 blend of 93/110 and we never again had any head gasket issues. The motor was a 10:1 flat top motor with N47 head. Pete Quote Link to comment Share on other sites More sharing options...
johnc Posted May 15, 2012 Author Share Posted May 15, 2012 Total advance - 36 degrees. CR - about 9.5 to 1. 91 octane. Quote Link to comment Share on other sites More sharing options...
z-ya Posted May 15, 2012 Share Posted May 15, 2012 Total advance - 36 degrees. CR - about 9.5 to 1. 91 octane. I'd say detonation caused the damage. Might have been a lean condition that caused the detonation, or just the fact there isn't enough octane in that west coast 91 octane fuel. I would suggest a 50/50 blend of 91/race just to be sure you have enough octane. What head and cam? Carbs, EFI? Was it dyno tuned with a WBO2 sensor? Quote Link to comment Share on other sites More sharing options...
rsicard Posted May 15, 2012 Share Posted May 15, 2012 Is there a corresponding trace of evident hot spot on the cylinder head/valve chamber or piston? What material are the pistons composed of? Are the pistons flat top configuration? Post pictures of the combustion side of the cylinder head. Suspect there is a hot spot, on the piston or cylinder head/valve near where the gasket was burned through. With a good head gasket in place, what does a leak-down test reveal? Quote Link to comment Share on other sites More sharing options...
johnc Posted May 16, 2012 Author Share Posted May 16, 2012 No pics of the pistons or head. Its a flat top L24. Just did a full compression test and the average of three after the engine builder installed a new head gasket is: #1 - 182 #2 - 153 #3 - 164 #4 - 175 #5 - 170 #6 - 172 I didn't do a leak down test but pressurized #2 and #3 to listen for any leaks past the head gasket. Didn't hear any. The car is getting checked for air/fuel ratios and will get put on a chassis dyno for carb tuning. I'm not really an engine guy so its time to refer it to the Weber experts in the area. Carbs are Weber 40 DCOE 18s with 32mm venturis. Quote Link to comment Share on other sites More sharing options...
rsicard Posted May 16, 2012 Share Posted May 16, 2012 There is a significant variance on the number 2 cylinder. Suspect there is may be a valve leak there. Thus the reason for the leak-down test wherein the leak can be listened for via the crankcase (rings), intake and exhaust to see which are at fault. Without adequate testing and tear-down it is difficult to make and absolute assessment. Testing EGT for each cylinder may reveal something. Quote Link to comment Share on other sites More sharing options...
rayaapp2 Posted May 19, 2012 Share Posted May 19, 2012 Chech for block or head irregularities in the area. Even a 0.002" "wave" in the surface (cumulative-0.001" on the head, 0.001" on the block) can alter clamping forces enough to make it susceptible to blowout when you hit some in audible detonation. I had an Isuzu/Chevy Luv that repeatedly blew head gaskets in the same spot. Instead of decking the block (which had what looked like a "rusty spot " there, at the recommendation of a former Isuzu Engineer I placed a triangular piece of stainless steel shim stock on the area with red RTV and damned if it didn't stop the issue. He said in some cases 0.001" shim would be used instead of milling the surfaces and screwing to the blueprinted centrelines... I can confirm this possibility. I consistently blew gaskets on a L24/N42 setup many years ago. It would blow between cyl #4 and #5 leaving me with 2 dead holes. It was a combo of slightly lean (running stock SU's) and poor surface condition between those cylinders. That made it the weak point that blew every time and in pretty short order. Quote Link to comment Share on other sites More sharing options...
johnc Posted May 19, 2012 Author Share Posted May 19, 2012 Overall air fuel ratios under full throttle and at high rpm are good. Lean at idle. The car is going to another tuning shop to do some further checking on the individual cylinder mixtures. Quote Link to comment Share on other sites More sharing options...
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