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langleytw

Re-using original pistons

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Morning folks,

Been busy pulling the motor apart and inspecting things as I go. All looking good so far with no horror stories.

I'm trying to be realistic about the 907 motor and what I'm going to be expecting of it. It's very easy to get caught up in replacing a multitude of parts without really needing to and I'm trying to resist that urge. My wife is very good at resisting that particular urge as is my wallet!

So the motor will be for road use. Not thrashed (because that's going to cost me a gearbox or something else expensive). I'd rather just pose-about really and, to be frank, retaining the 2.0L means accepting it's performance limitations.

So I don't think I need a set of forged pistons and would like to re-use the originals. The motor has done 48K miles and for the last twenty years virtually nothing.

The pistons have been kissed by the valves at sometime (probably valve float as std cams in place). Judging by the lack of sharp edges and the 1mm of carbon on the crowns, I'd say this was early in it's history and has had no subsequent ramifications. Skirt wear doesn't look bad, so if the bores are ok I'm sorely tempted to polish and re-use them. Am I being too tight on this one?

Photos attached.

Any opinions gratefully received.

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Actually they do look a little bashed.

 

That said all they really do is hold the rings. I used my old pistons on my turbo which had 48K miles on it. Going to forged pistons would be mad if you asked me. Id use those or maybe a second hand set if cheap enough from Lotus bits.

 

Buddsy

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Hi Tom,

 

Sorry, can't help with the pistons but just to say enjoy the 2.0 for what it is. I've been tempted to increase the performce on mine but at the end of the day I'd rather enjoy the original performace of the car and the engine that was intended for it. The fact is you can make the 907 scream and have a hoot without worrying about the gearbox in our cars. If you want a faster car buy one that was meant to go faster in the first place, that's what I say.

 

Pete

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want to go faster?.... buy a faster car..... the S1 Esprit is a beautiful car to drive and the engine is a peach.

 

Those pistons are fine too.

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Looking at the third photo down...the lower piston. Don't understand the marks on the piston crown...there seems to be four "V" shaped grooves ? Very puzzling. I would have thought that any piston/valve contact would have resulted in bent valves...not grooves corresponding to the outside of the valve heads. The angles between piston and valve mean that they should hit "flat" in a fore and aft direction...the valve stems go up and down at right angles to the piston head cutaway machining, so how "V" shaped grooves got there is beyond me!! If the engine was working OK before you took it apart, then the possible valve/piston clash has already been dealt with.

Check the valves for straightness...roll them on a flat surface and see if they wobble(!)...clean the pistons up, but don't use any abrasive polish...3M scouring pads are good for the carbon on the tops. Before you reassemble it, inspect the bores and (ideally) hone them to a light crosshatch. New rings would be worthwhile...and the honing will aid the "breaking in" process...run on normal oil during this period and then consider changing to synthetic. Make sure the ring gaps are good and they are 120 degrees apart on the pistons...splash out on replacing the bearing shells, mic up the crankshaft and ensure it's still within specs, mine's done 110,000 miles by now and has had a few sets of bearings and she still has 50psi+ oil pressure.

I could blather on forever......the essence is, putting the old pistons back will be fine.

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You beautiful people...and saving me money! The bills really start to add up fast on these cars.

 

Yes, I don't understand the orientation of those dings either. What's even more weird is that #1 has been hit on Ex side but #2 & #3 hit on the inlet side???? #4 unscathed. But the engine was running strongly before the tear-down (compression test all good) just worn valve guides with the accompanying volumes of blue smoke. Crank should get away with a polish. I've never seen such an over-engineered 2.0L crank. I don't know if it's the original head (can we tell?).

Glad I stripped her down though. There was a ton of sludge and crap in the sump and the oil feed mesh was well and truly blocked 25%.

Thanks again,

Tom.

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If they measure up ok, ring grooves in particular, I would re-use them, but I'd polish and smooth any dings or grooves on the crowns to prevent hot spots, and possible pre-ignition.

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You beautiful people...and saving me money! The bills really start to add up fast on these cars.

 

Spend the £20.00 supporting this forum and get the 10% off at Strattons which will save you a lot more. As well as being able to down load the parts list and also help the forum keep up and running.

 

I dont get any of it as a Mod by the way. :thumbsup:

 

Buddsy

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I dont get any of it as a Mod by the way. :thumbsup:

 

Buddsy

Quite right, the kudos alone should be enough :-)

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They came up pretty well. Perhaps I'll just have to get a high lift cam so I can cut out the marks for the valve reliefs!!!

Thanks for the advice. I feel quite happy to use them. Must have been a missed gear or such like I'm guessing.

Now, where's that credit card?!

Cheers,

Tom.

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Just make sure you put them back in the correct order they came out of the bore and you should be fine

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I went through this same process a while back and on mine the up/down movement of the piston rings in the piston was out of spec and the liners were oval and out of spec. The exhaust valves were too far gone and the valve guides were worn. So.... £3k later it now doesn't have that wear!

 

I thought about putting a 2.2L engine in it but I wanted to keep it original as far as possible. Unfortunately my head had been skimmed once too often and the cam carriers were also worn so it's not a truely original engine anymore :(

 

Paul.

Edited by Paul Coleman

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