So I have to bore my cylinders...

[Preyupy]

What size are the pistons in the block now?  It is hard to imagine it is still a standard bore after 40 years.  Then you need to take the block to a machine shop and find out how much they need to over bore it to clean up bore. THEN order your pistons.  Do not have them bore the block until you have the pistons in hand!!!!  Then make sure they know the proper clearances for the pistons you have (this May or MAY NOT be the same clearances called out in the BMW repair manual) as specified by the PISTON manufacturer. 

[TobyB]

QSC makes semi- pro audio gear.

 

Those pistons are odd- wonder what sort of compression ratio you end up with?  And no rings?  

Is that a UniDome for piano, peanut, and 1.8?  E21?

 

 

I R Skeptikal.

 

t

 

[rstclark]

I have had good  experience with Ireland Engineering 9.5:1 pistons for an E12 head  They are Mahle knock offs for $460 a set with rings. 9.5 :1 compression is very tunable and will go well with your 292 cam

The pistons are for the second overbore of 50 mm. They are cast of the same alloy as Mahle, so the bore clearances are the same as stock -- plus 1.5 thousandths I believe.

Here is the detail you need to pay attention to.. The piston size  will be different for each piston.

I'm working with a closely balanced set that have a difference of 2 thousandths between the smallest and the largest. You will have to find a machinist who will measure and bore each cylinder to match each piston

The process is to bore the cylinder and then hone the cylinder to the exact match and clearance for each piston. This will cost a little more than your standard machine shop bore job -(I've been quoted $40 extra) but it is a must.

By my measuring the pistons are also a little oval in shape , a little smaller at the pins , but I'm told that this is no big deal.

When you get the bore done, check the ring gap. Rings are not perfect either. Find the best ring set for each cylinder then put them on the piston for that hole before things get confused

Regardless of what pistons you use,  find a high quality machine shop who understands what needs to be done. You might tell them you have pistons of different sizes and want the block bored for each piston just to see what they say.

If they can tell you how they will do it then good. If they say  Na you only need to  bore the same size, don't do business with them.

This might be the last set of pistons you will ever need in a 40 year old car  and the last set that will fit your block so get the best pistons you can and find the best machine shop  It will be money well spent

Good luck with your project.

[Mark92131]

15 hours ago, TobyB said:

I R Skeptikal.

 

QSC Piston Review...

 

 

Mark92131

[oldguy]

On 3/23/2017 at 11:03 AM, Naz said:

If you need a set of rings i have an extra set for 89.97 pistons that I don't need. Although, you should get the rings with the pistons.


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Are you sure they are for a 90mm piston?  A 1mm oversize?  or are they for stock?  If they are for 1mm oversize, I will take them.

[Naz]

 
Are you sure they are for a 90mm piston?  A 1mm oversize?  or are they for stock?  If they are for 1mm oversize, I will take them.

I will send you a picture and the specs when I get home Tuesday. They were meant to go with my 89.97 pistons you see in the picture I posted of the engine. I ended up using the ones that came with the mahle pistons instead.




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[worzella]

Hi - I am in your exact same position in my project. I have an E12 head and a block that has been bored +25. I am still awaiting the machine shops verdict on the bore measurements, but my last post listed a few options (search on my ID).

 

But seems I am looking into these three options, all expensive and not going to show up on your doorstep the day after ordering:

 

o W&N cast Mahles in a +25 or +50 standard overbore About $800 I think

 

o Ireland Engineering forged set... about $700 but seems you can specify all your specs, bore and compression desired.

 

o Top End Performance - forged JE pistons for about the same $700 price and again made to order for your specs.

 

Randy 

 

 

[worzella]

rtsclark - you said Ireland has cast +50's... When I visit their web site, the only cast ones I see are a full +1. 

 

Do they offer other cast sizes that are not on their web site?

 

I guess I need to call them and not trust the product selection listed on their site.

 

Thanks -Randy 

[avoirdupois]

On 3/22/2017 at 6:20 PM, flagoworld said:

Which means I need new pistons...

 

Although I can guess, I don't believe you mentioned why you need a rebore.  When reboring is not the best option, cylinder bores can also be sleeved.    Possibly permitting piston reuse.

 

cylinder sleeves

Edited March 25, 2017 by avoirdupois

[flagoworld]

Thanks guys. I'll know more soon. Will let you know as soon as I do. I know they did a quick measurement, but I guess the block guy was out for the week so I have to wait until next week for more numbers. They will be "pre-boring" to equalize the bore with the smallest portion of the taper, and then figuring out boring options from there based on the pistons I choose. I will have exact specs soon™

 

About 90% sure the pistons and bore are original from 1974, but I really should have checked before sending them off. I want to say I measured the pistons and they were around 88mm or something. Can't remember.

[rstclark]

Ireland cast pistons are for the second overbore I think that means plus 50 mm but check with them

[oldguy]

Lemme clear something up.   Std  First over  Second Over.  

 

In America.  STD is the factory hole size.  First over is sometimes called "Twenties".  or 0.020" over which is 0.5mm.  Second over is "forties" or 0.040" or 1mm over. (Some engines like Small block chevys etc will have 0.060 and 0.080" bores as well)

 

Europe has this love affair with tiny oversizes.  Sometimes (depends on engines and we are leaving air-cooled stuff out of this since that just messes everything up)  First oversize is 0.010" or 0.25mm.  Second oversize 0.020" or 0.5mm and then sometimes they will do a third oversize of 0.040" or 1mm.   Other times they will stick to the traditional norms of twenties and forties.  It varies by engine.  

 

To an American machinist, they will look at you like you've lost your ever loving mind if you show up with .010" pistons.  Here's the reason.  Your hole is out of spec and IIRC the out of spec on an 02 cylinder is like 0.003" too big.  So you've got to understand the limitations of the equipment.  A dial bore gauge measures diameter across the bore but not in reference to the centerline of the hole.  It's just the distance across the hole.  The wear in the bore is usually on one side.  The thrust side.  So a prudent machinist will locate off the bottom of the cylinder, where ring travel is minimal and there is little wear.  Now boring a hole 0.010"  (first oversize) in some engines goes like this.  Set the machine up for 0.008" bore which is really only .004" off each side of the hole.  Then you are going to hone out the last 0.002" of the bore to achieve a proper surface finish.  Now if everything is great then yes, first oversize would work but in reality, the engines don't have sealing problems until .004-0.005" wear is in the bore.  By that point, the hole won't clean up at 0.010" over.  As much as people feel that the least off is the best, the reality is that most blocks will require at least 0.020".  What ends up happening is 3 of the 4 holes clean up but one has an eyebrow looking wear spot at the top of the rings that won't clean up and then you do the job all over again.  Most customers don't want to pay twice and most machinists are not working for free.  So either buy the size he says will work or be prepared to loose it all.  You can always sleeve a block to standard, that is where you cut out like 0.125" out of the block, press in a new cast iron liner, and then bore it back out to standard.  Obviously expensive and time-consuming.  I know the local shop here charges $80 a hole + the sleeve which is around $30-40.  A sleeved block will need to be surfaced as well.  It's possible to do it without but you need a very skilled hand and it still won't be as nice of a job.  

 

Now, back when these pistons were made, there were two ways of clearance.  The clearance was in the piston or in the hole.  A piston has about a 0.002-0.003" clearance between the bore and the piston.  This is for expansion. Aluminum piston vs cast iron block.  So a Mahle piston is like 88.97 (stamped on top).  This indicates to the machinist that the clearance is in the piston.  Not in the hole.  Sometimes piston manufacturers made a 90mm piston for a bore that was 90mm.  So the machinist had to make the clearance between the two and measure it out.  So 90mm = 3.5433"  So if you've got a 90mm piston that needs 0.002" clearance then you need a 3.545-3.546" hole.  This is how sizing pistons is done, clearance is factored in, and the thought into a proper overbore size.

[jimk]

If it is a metric car, we should talk metric and dump the oddball imperial stuff, a dozen eggs, 16oz to the pound, 36 inches to the yard, 4 quarts to the gallon, and another thousand oddball definitions.

[ray_]

1 minute ago, jimk said:

If it is a metric car, we should talk metric and dump the oddball imperial stuff, a dozen eggs, 16oz to the pound, 36 inches to the yard, 4 quarts to the gallon, and another thousand oddball definitions.

 

 

Hey,

 

What size are your tyres?

 

[rstclark]

If you talk to an American machinist be prepared to be bilingual