L18 bore 30 over

[DURAN]

In need of some help my l18 is currently in the machine shop & needs to be bore 30 over 

My question is were & what piston can I use motor is stock I am not a mechanic by any means I am learning as I go 

Any help is appreciated  

[Stoffregen Motorsports]

This thread has info and part numbers -

 

[banzai510(hainz)]

L18 piston. see if soemone have 030 or  040 over

[Crashtd420]

Dont let them bore the cylinders till you have the pistons.... just my opinion.....

[datzenmike]

0.040" is about 1mm so beware a '50 over piston' as it could mean a 0.020" (or 1/2mm) and not a 0.050". Measure twice... bore once. 

 

You could use .5mm or 1mm oversize L20B pistons and mill the head to make up the loss in compression. You only need to loose less than 4cc.

 

Yes, present the pistons to the machinist when ready to bore. No piston is ever exactly 86mm. The piston to wall clearance is between 1 and 2 thousandths of an inch. They need to be measured and bored and honed to the correct clearance.

[DanielC]

"Dont let them bore the cylinders till you have the pistons.... just my opinion..... "

Not really an opinion, more of a necessity.

[Crashtd420]

6 hours ago, DanielC said:

"Dont let them bore the cylinders till you have the pistons.... just my opinion..... "

Not really an opinion, more of a necessity.

Wasnt sure if I was right or wrong saying it but it made sense to me... thats what the machine shop did on my engine.. and everthing toleranced perfectly during assembly....

[datzenmike]

Nissan pistons (L20B for example) range from 84.985mm to 85.035mm and the bore 85mm to 85.050mm.  Bores and pistons are measured and marked 1 through 4. When assembling, the worker looks at the grade number of the bore and reads a (3) he selects an oversize (3) piston for a perfect fit. This allows a slightly over or under size piston to mate with an equally over or under size bore and saves a lot of waste. 

[datzenmike]

16 hours ago, datzenmike said:

 

 

You could use .5mm or 1mm oversize L20B pistons and mill the head to make up the loss in compression. You only need to loose less than 4cc.

 

 

 

Milling the head down 0.25 to 0.30" will reduce the combustion chambers by close to 4cc each and allow over size L20B pistons to be used.

[john510]

Good luck finding L-18 oversize pistons.

[Stoffregen Motorsports]

3 hours ago, datzenmike said:

Nissan pistons (L20B for example) range from 84.985mm to 85.035mm and the bore 85mm to 85.050mm.  Bores and pistons are measured and marked 1 through 4. When assembling, the worker looks at the grade number of the bore and reads a (3) he selects an oversize (3) piston for a perfect fit. This allows a slightly over or under size piston to mate with an equally over or under size bore and saves a lot of waste. 

Machine shops do it a bit differently. With pistons in hand, they measure each piston and then bore the block and finish hone it to the required piston to wall clearance. I don't know of any good machinist that would bore a block without having the pistons first.

 

Most piston sets these days will have matched piston diameters. Only the OEM pistons came in in-between sizes. Aftermarket piston MFG's don't bother.

[banzai510(hainz)]

as mentioned might be hard to find L18 4cc dished pistons. Most are L20b 11cc dished which will fit but lower the comp down to much.

Theres a place is Australia that still had pistons I think.  I had bought some Fedral Mogel ones back in the day when they were cheap

[datzenmike]

Crap they are 4cc???? Forget milling them.

[scooter]

Just get standard 280 flat tops and bore the extra .010. It takes like 10 minutes in a hone to knock that much extra material out. Or whatever flat top 280 pistons you can find. Bore the fuck out of it, make some powaa 😂

[Stoffregen Motorsports]

That's what I would do.

[datzenmike]

Agree but get it bored professionally for perfectly round and no taper  

[docbainey]

L18 Flat tops, std, .020, 040 & .060

 

From down under.

 

https://www.precisionintl.com/Engine.aspx?ID=1325&EID=3507

[datzenmike]

You can also build from spare easily sourced parts here...

 

Over bore your L18 2mm to 87mm. For best ring seal you should machine to some over size anyway.

 

Use L16 rods..................... 133mm........ they are everywhere.

Use 87mm Z22S* pistons.... 35.5mm.... used are fine if in reasonable condition or new.

L18 stroke 78mm/2.............39mm

Total.................................. 207.5 and the L18 deck height is 207.85mm so tons of room.

 

Displacement........... 1854cc

Compression.............. 8.521 with 45.2cc open chamber head and 9.32cc* dish Z22S pistons.