L26 engine pistons

[fluegel]

I have a 1976 260z 2+2 with its original block I had the engine reconditioned in 2006 with new pistons which I assume were replacing the same type as as it had before. The question is these are dished not flat tops but my reading seems to indicate that they should be flat tops for an engine of this date in this car. Would this be correct for an Australian market model or has someone changed them , i cant see why as it would reduce the compression ratio.

Richard

[gilltech]

My original '74 260's motor has dished pistons. AFAIK the 260's didn't have flat-tops as they ran lower compression than their 240 predecessors.

[fluegel]

My original '74 260's motor has dished pistons. AFAIK the 260's didn't have flat-tops as they ran lower compression than their 240 predecessors.

 

Thanks for the info, I plan to replace the head with another one closer to original thickness so I can reinstate the standard timing chain tensioner setup. As the comp. should be low enough to use 91 octane (I think) is there any advantage in using 95 or 98.

 

Richard

[260Coupe]

Standard L26 compression is around 8.5:1 so no advantage in using Octane > 92......just wasting $$$ on fuel

 

Install flat top pistons, this will increase comp to approx 9.6:1 and use 98 octane.....immediate 10-15% HP/torque

[d3c0y]

Putting a lower comp head on it will only make the car slower.

[fluegel]

Putting a lower comp head on it will only make the car slower.

 

True, but I need to get the camshaft sprocket high enough to take up the chain slack so I can use the standard tensioning setup. At the moment I have Kameari twin sprocket tensioners which work really well and solved the problem but I can't stand the noise, BTW the timing  gear is new. How easy is it to fit new flat top pistons if I want the extra power. On the other hand I remember with this cars original head which I presume was close to full height the engine was poweful enough for my needs. The present head is 105mm high there are  cam tower shims in place but not enough to get the cam high enough. Another option would be to use the present head with a copper head gasket shim but I believe these can have problems.

So to sum up here are my options to go back to the standard tensioner setup.

 

1:Replace the head with the 'new' one which is 107mm thick and loose some power.

2: use the present head with a copper gasket.

3: Put thick enough shims under the cam towers (I had decided that wouldn't work but I could be wrong).

4: New low compression head and flat top pistons to increase power.

5: Fix the problem without spending too much, use this car for general driving, and buy a well restored 2 seater Z.

 

Richard.

 

.

[d3c0y]

Just get an L28 for it, it will be better than any of that mucking around.

[dat2kman]

Richard,

You can slot the curved chain guide inwards on its mounts to front face f block, and, the oil plunger tensioner can also get it mount holes to block front slotted, but make sure to mill a slot (2mm wide) on the back of the oil plunger block so as to pick up the oil delivery hole at block, modify the gasket too.

 

When you go to bolt the iol tensioner assy to block, you need a couple of half round bits of metal, a roll pin cut lengthwise will do, these are placed into the now slotted holes of the tensioner block, so as to pisitively stop the plunger assy from being pushed backwards

 

Expect a bit more wear on the curved guide, you will need to dummy assemble engine without front cover, to make sure it all lines up.

The curved guide may need a bit of weld dabs in its mount holes, also to stop it sliding back.

This method has been used on many L engines, rough, but works.

 

Yes the twin dler pulley setup is noisy, but it does take up a fair bit of slack.