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Sylva Member
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I run a 2.2 910 Block with all the mods. And JE Pistons +30. I had the engine rebuilt, (In Malaysia,) by a good machine shop, (But not the best Mechanics). I ran the car for 5 track days up to 6,000 Rpm. Then raced it, And the Pistons hit and broke down to the 1st ring, on 1,2 an 3. When I stripped the engine I found that the dowels to locate the head gasket were not in place and thrfore the gasket and linner bores were no aligned. So the Pistons had hit the chrome ring of the gasket.911.25 CR Pistons). So rebuilt the engine By some one else who I trust, using 10.5 CE Pistons from JHPS. Ran the car for 4 track days no trouble, then raced it at up to 7000 rpm and same thing, 1, 2 and 3 Pistons broke, but this time the gasket was aligned and the pistons have hit the head. So my question is, does any one have any experience of this problem. MY thoughts are that the rods have streached (sould be 5.5 inches +001 between centres), and I'm pulling the rods out to check this weeknd. Head has never been reground, and valves are not hitting. And head Gasket is the right one, I'd apprecate any advice, including where you guys buy your steel rods from. My source at Lotus tell me that there should be no problem with rod stretch until at least 8,500 rpm and I didn't get near that. |
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Dan Eiland Member
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Have you checked the distance from the center of the pin to the top of the 2.2 pistons? Have you checked the roundness of the liners? Is there any evidence of it hitting somewhere? Maybe you have a lip around the tops of the liners causing the pistons to fail when it hits the lip? Sorry I can't be of much help. Might get some input from some of the racers or engine builders on the board. |
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Sylva Member
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No its not hitting the Liners, I can see where it has hit the head. |
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Ron Earp Member 
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This is odd. So, if it hits the head and not the valves then it hits the head on the compression stroke I think, otherwise it'd hit a valve. And none of your valves are hit? When the engine is assembled and at top dead center what is the measurement from the top of the liner to the top edge of the piston? Ron |
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Judson Manning Member 
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Sylva, Just to help everyone else, I'm listing a number of different piston Compression Heights I've assembled over the years: 2.0 Configuration: Stock=1.615", JE Flat-top=1.640" 2.2 Configuration: Turbo=1.470", JE Flat-top=1.480", JE 'H/C' Flat-top=1.535" All use the 5.5 rod (Turbos use different rod-bolts) including the 300HP Esprit S4 SE. The 2.2 JE 'h/c' Flat-tops I understand are a special designed by Garry Kemp available on the shelf from Delta Motorsports. As is the case with the 2.0 Flat-top, the 2.2 JE 'h/c' is a zero-deck-height version of the stock/regular flat-top piston. Complicating matters when it comes to compression ratio is the newer head gasket that is about 0.020" thicker than the original. Back to the problem... Assuming you are NOT using the special H/C JE pistons from Delta, and you ARE using the newer head-gasket; there should be about 0.050" - 0.070" clearance between the head and the top of the piston. Even an Aluminum rod won't stretch that far. I think the problem is elsewhere, and may be a combination of effects. Could the engine be leaning-out at that higher RPM? Any idea of what Exhaust Gas Temperature you are running at that RPM? I assume you are keeping the engine operating temp well below 200^F? What about piston-to-wall clearance and ring gap? Again, with high temps, lots of RPMs, a lack of oil, and no where to expand; the pistons could simply be heat fracturing. I want to stress the JE pistons supplied by JHPS are of VERY high quality design. I run them in my cars as well as engines I've built for numerous clients. However, it may be that in a racing situation at sustained RPM levels; you may need an alternate design. Judson Last edited on 11-13-2006 09:10 pm by Judson Manning |
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Jim Ketcham Member
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This is interesting. Typically when the "squish region" (space between top of piston and bottom of head) is too small you first detect it when the engine is run cold. At idle it sounds like a diesel. As the engine warms the rap goes away. The reason, I have been told, is that a cold unexpanded piston rocks letting the edge make contact. As the piston heats up and expands it no longer can rock within the cylinder and the noise disappears. This was an issue in some mid- 90's Mazda engines (and Ford Probes that used the Mazda engine) when Mazda reduced the squish region to help lower emissions. A slight carbon buildup on the top of the piston resulted in "rap". Your having contact at hot conditions and not at cold is a reversal that is perplexing. Definitely one to think about. Jim |
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Sylva Member
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Hi Let me deal with the points raised. First engine I had trouble with was a 911, that came from my Rally car, this was used as a support car when Henry Tovinan won the WRC in early 80's and had a few works goodies(but not al) and was 180 bHp at the wheelsl. When I put this engine in my race car it blew from Oil surge, So I surced a NEW 910 Turbo block and crank and this was used with +30 JE Pistons supplied by Garry Kemp. Engine wa assembled locally in Malayisa and run at 6000 rpm fine for 4 or 5 track days say 100 3 mile laps. Then used in a race, at 8,000, engine run bad after two laps and when the head came off, I ,2 and 3 pistons were broke down to the top ring. At the 12 o'clock poition looking at the engine. But the head dowels to locate the gasket were missing and the gasket and bore did not line up, so It looked like the piston was hitting the gasket ring and the gasket hitting the head. So happy I knew the problem the engine was rebuilt with pistons supplid by JHPS. Ran for 4 track days, no problem, no noise, and certainly not 'like a deisel' Ran car in race at 7000 rpm and started to mis fire. Removed head and 1, 2 and 3 pistons broke to top ring (Gasket Chrome ring was fine), again at 12 o'clock position. My plan is to remove the rods and check 1, 2 and 4 against number 4 (which has not been a problem). Thanks for you comments and good wishes Kelvin |
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Sylva Member
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I measured a few things on Number 4 cyl last night, I need to wait for the weekend for the others.as they are damaged and I need better light. Piston stands out of the head at TDC by .050 inch. Piston Clearance in the bore, is 0.030 Inch, Using the +30 CE Piston. This appears to me to be very large, Lotus spec on Std Pistons in Cast Iron Linner is 0.005 inch. I'dd appreciate advice and experience on this. So if the piston 'rocks' in the bore it would move the piston out aboot a further 0.015, (3.75 Bore and say a 2 inch piston skirt. less with the Piston expansion) Plus rod stretch of 0.020, so stand out could be .050+.015 +.020, or .085. Which is 2.1 mm, Need to get the exact thickness of the head gasket, over the weekend. But looks like the Piston clearance could be my problem. Kelvin |
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