9 replies to this topic

[Orange-Phantom]

Hello,
 
I'm just throwing this out there as someone may know the exact answer and put my mind at rest.
 
I'm taking the engine out of Project 45 for a couple of reasons.
 
It's leaking a small amount of water from between the front of the block and cylinder head (yup head gasket leak) and they have used a copper head gasket and I'm thinking the BK450 is going to be better.
The main reason is that  I'm changing the final drive to 3.7 as a 3.1 ratio on the 6 speed is far too long and I'll be able to keep the revs up to a more suitable level and use the gearbox more, plus I can sort the gearbox remote out so I don't have to pull the gearstick up (like you do for reverse) to get it into 5th or 6th (trying to find the gate can be fun)!
 
After taking the cylinder head off I notice that there is quiet a gap between the piston and the side wall (I'm yet to measure it but want to take the gearbox off first to measure it properly).  I can move the pistons by hand quiet a bit and also when I turn the engine by hand (back and forth) there is quiet a bit of side movement on the pistons which is kind of worrying me.  The pistons are JE Forged which I know are meant to have a larger gap.  (I've not had much joy in finding any specs off them).
 
The engine doesn't consume or burn any oil so...
 
I'm thinking I'm worrying myself unecessarily, but does anyone know what the clearance should be for forged pistons on a 1380 should be.
 
Thanks guys n' gals.

Attached Files

•  20160316_082031_resized_1.jpg   42.07K   27 downloads

Edited by Orange-Phantom, 16 March 2016 - 11:01 PM.

[kezzkitkat]

Try a bore gauge to the Pistons size there is a tolerances quite a few different opinions but generally between 2-4thousands
My je ones they. Said 2.5 /3 is fine anymore they said you will have ring issues hope this helps maybe worth contacting minispeed as they stock a lot of je Pistons
with in this aswell as piston rings but only way to check that is removing Pistons and etc which is a full rebuild with new rings
I've never got on with copper always 450 a lot less insures

[carbon]

The gap at the top of the piston is normal. You need it to allow for expansion when pistons get hot, and forged pistons typically run with wider clearance than cast.

 

Measurement of piston to bore clearance is made at the bottom of the skirt at 90 degrees to gudgeon pin axis. That's the measurement which really matters.

[mini13]

yep, clearance at the top can be alarmingly big,

 

pistons are made a weird shape, so that at runnig temp they fit the bore, the normal place to measure a piston is on the skirt at 90 degrees to the pin about 1/3 of the way up as below.

 

http://www.dansmc.co...sure_piston.jpg

[MRA]

That weird shape is oval and tapered in most cases... there was a company experimenting with very oval pistons, not sure what came of it, but they where visually oval, it might have been Honda, but it was a long time ago...

 

0.0025" (0.0635mm) is fairly common size, you would increase it for racing and decrease it for methanol.

Edited by MRA, 19 March 2016 - 12:53 PM.

[Mini Manannán]

That weird shape is oval and tapered in most cases... there was a company experimenting with very oval pistons, not sure what came of it, but they where visually oval, it might have been Honda, but it was a long time ago...
 
0.00

The thoroughly bonkers NR750! https://upload.wikim.../Ovalpiston.jpg

Edited by Mini Manannán, 19 March 2016 - 05:59 PM.

[MRA]

 

That weird shape is oval and tapered in most cases... there was a company experimenting with very oval pistons, not sure what came of it, but they where visually oval, it might have been Honda, but it was a long time ago...
 
0.00

The thoroughly bonkers NR750! http://thekneeslider...r750-engine.jpg

 

 

That might be the one...... but I get a "forbidden 403" error code

Edited by MRA, 19 March 2016 - 04:18 PM.

[Mini Manannán]

 

 

That weird shape is oval and tapered in most cases... there was a company experimenting with very oval pistons, not sure what came of it, but they where visually oval, it might have been Honda, but it was a long time ago...
 
0.00

The thoroughly bonkers NR750! http://thekneeslider...r750-engine.jpg

 

 

That might be the one...... but I get a "forbidden 403" error code

 

 

Found a better link.  it is taking it to absolute extremes and veering way off topic ....

Edited by Mini Manannán, 19 March 2016 - 06:03 PM.

[MRA]

Some useful reading...

 

 

Attached Files

•  SB2169 - PISTON SKIRT CLEARANCE.pdf   150.69K   23 downloads

[Orange-Phantom]

Cool, thanks guys.

 

Methinks I'm just panicing a bit unessessarly!

 

Engines coming out very soon so I'll check when the gearbox comes off.