engine bore, piston and ring sizes

[.]

I have tried searching but surprisingly I didn't find anything that answers the following for me:

 

What is the most you can bore an L28 before you start risking hitting oil and cooling galleries?

 

I believe a standard L28 runs 85mm pistons in a 86mm bore giving a 1mm gap (diameter). What is the maximum gap that can be run? (I have 86mmm flat top pistons, whats the maximum bore I should consider)

 

 

 

 

 

[salty]

Honsowetz says 2mm,80thou

[PZG302]

Greg,

 

All my L28's have been bored to 3mm oversize no problems, but it is wise to get your block sonic tested before hand.

 

With a 3mm overbore there are some pistons available, Jason has the details of the pistons he uses, Honda from memory, in one of his threads. I currently use custom pistons for my current build, the previous pistons that are now ashtrays were a Ralliart piston that is NLA.

 

If you are looking at using pistons you already have then get your machinist to set the block up to suit.

[luvemfast]

The engine that Peter Mac is building for me is 3mm oversize.

I'm running a girdle and Arizona Z car sump to add rigidity.

 

In regards to the girdle, some say its not necessary. I beg to differ, as its my money that has been invested in the motor.

[peter mc]

the L28 bore is 86mm standard and the piston is also 86  ... 87 mm flat top pistons are easy to get from most zed shops if you wont bigger pistons you can have them made by JE or CP in the US or have them made hear by sps in melb , i like to go 88mm

[salty]

Pete is full of info as usual, got to bre, er, thats meant to be "be" the "go to guy" on this forum

Pete , can you post the suppliers for those that want the parts?

Pete, your info is excellent!

[zr240]

If you want some prices on 86 and 87 mm Japanese flat tops let me know and I can get some when I'm in work tommorow. I used to run them on my own race motor back in the day. They are a great piston if you don't want to go the extra step of forged/ custom ones.

 

 

Pete is it safe to go to 88mm on all l28 block or is there risk of getting the bore wall too thin? Or do you sleeve it?

 

Ash

[peter mc]

yes 88 is safe ..  89 is as far as you should go .i sonic test when i go 89, the last L28 i tested had 100th left in the wall in the thinest place . if you wont 90 you will have to put sleeves in it to be safe .. it a good idear to test all race motors for peace of mind . it will be good if ash can find some 87mm flat top cast pistons as they are great budget piston for the street zed

[1600dave]

If you want some prices on 86 and 87 mm Japanese flat tops let me know

 

How about 87.5mm ? I rebuilt my engine last Easter and 87mm were easy to find (which is what I used), 87.5mm not so easy (which is what I wanted to use but couldn't find).

 

Also curious if they can be obtained in sets of 4. I'll be building another engine later this year, would be good to know availability.

[zr240]

Thanks for the info Pete.

 

Will get some prices and see if I can get set of 4. I am pretty sure thru don't do 87.5 but will double check.

 

Ash

[Riceburner]

I got my 87.5's from SW motorsport, off the shelf.

[zr240]

So .040 over is 1 mm bigger bore 87mm

Is .060 over is 2 mm bigger? Or 1.5mm bigger?

 

Ash

[Patch]

Google can help with every thing .

Your Answer…

You asked:

.060 inch converted to millimeters

inch

inch

millimetre

millimetre

1.52 millimetres

 

Standard bore size is 86mm  Maximum overbore with out sonic testing 2.0mm or O.080-in

[luvemfast]

40thou =1mm  (Ø87)

80thou =2mm  (Ø88)

120thou =3mm  (Ø89)

 

[luvemfast]

Thanks guys for all the great info. I'm still unsure about the gap. If the measurement across the top of the piston is 86mm does that mean it would be best for a 87mm bore or can they be used in a bigger bore? And what rings do i need?

Ø86 piston to suit Ø86 bore

 

[dazzed]

Ø86 piston to suit Ø86 bore

for that perfect fit we all are ultimately looking for!!!!

[luvemfast]

for that perfect fit we all are ultimately looking for!!!!

Tolerance not stated.

Point being, an Ø86mm piston doesn't use an Ø86.5mm bore.

So -

Ø86 piston to suit Ø86 bore

 

 

[zr240]

Unfortunatly they only have the std flat tops in stock at the moment.

 

The pistons are $215.00 inc GST

Rings are $119.00 inc GST

 

They are going to get back to me on the .040 and .060 as to when they will be back in stock.

 

Apparently they will be the same price as the std??

 

Ash

 

[d3c0y]

I've read about a few cars pushing it out to 90.5mm so you can get 3.2L with V07 crank.

[peter mc]

standard clearance is 2.5 thou to 3  for cast pistons and 4 to 5 thou on forged race pistons as a rule .

and you can on some blokes go to 90mm but the walls are to thin and you will have oil control problems

 

[luvemfast]

For those of us who aren't dinosaurs. 

What is the metric equivalent?

0.06-0.075mm for cast

0.1-0.13mm for forged

 

Really? That seems large to me. Why are forged running bigger tolerances Peter?

Thermolinear expansion would be the same wouldn't it?

 

[peter mc]

the forged pistons grow much more .diffrent metal, the cast piston is very stable and will not grow as much and can be run much closer and gives years and Meany thousads of km before they need to be changed . on a down side they can not see the same rpm or power levels as a forged piston, but for street driver they are the way to go, the close piston to bore clearance makes them quit and gives good oil control. forged pistons need to be wormed up so they can grow and seal, the

up side to them is they are very strong in the ring land this is important for turbo and blower applications as cylinder presher is much higher than NA engines

 

your JE pistons are 3-5 thou  depending on application

[luvemfast]

Thanks for that Pete, ya dinosaur 

[dazzed]

OK but I am obviously still missing something. Does an 086mm piston actually measure 86mm across the top? What is the normal tolerance?

85.85mm at the top and 86.465 across the lower part of the skirt for a standard cast type piston because the top is exposed to the combustion and heat is transmitted through the skirt and into the cylinder walls and then the cooling system , is that what you wanted to know , hope this helps cheers Daz

[Patch]

While we are bringing in fits and limits I will let you in on a bit of old Kiwi ingenuity that we used to do years ago, pistons were very expensive and if the bores were not to bad you would separate the rods from the pistons and after you have honed the bores and taken the ridge off the top you would insert the correct old piston into the bore upside down and tighten 2 bolts with a long nut in between the rod bore on the piston skirts, you tighten this until the piston grabs you do this at the bottom of the bore, now pull the piston out hold over a vice so the bolts can fall out and you heat the skirts until the bolts fall out and let to cool down, this stops any piston slap.

 

We would also keep the old oil control rings and machine the top and second ring grove so it is now square again and put the old oil control ring as a spacer.

now we would buy 10 tho over size rings and gap them to the std bores, and just check to make sure each piston fits with out grabbing if so just a bit of sanding to fit. Refit the rods and rings, this process was quite common and could be done at most machine shops. This process you could get another 60k miles before it needed re boring.

now pistons are cheap it would not be done much now.