Piston to bore clearance - 1600 build

rjplenter

rjplenter

True Classic
1600 build

I just dropped my block off to be bored and honed to fit our 87mm pistons. The machinist asked how much clearance there should be between the piston and bore for a 1500 block and I couldn't tell him.

Does anyone know? I don't have a workshop manual at work and a google search turned up nothing. I need to call him and let him know so he can start work on it.

Thanks!

Rob
 
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Where did you get the pistons? Usually the manufacturer provides spec on the appropriate piston/bore clearance.

Did you look at the piston crown - that info is also engraved, usually..

IMG_2937_zps7235b5d7.jpg


86.96 piston for 87mm bore so, .04mm for mine
 
Not always as simple as that

Your pistons have all the info right there Hussein!

Mine don't, all that is marked on the crown is 6/10.

I bought them online from a Greek seller recommended by Steve Cecchele. Unfortunately they did not come with a data sheet.

They are meant for an "87mm" bore, but they measure 86.55mm across the crown, 86.8mm half way down, and 87mm at the lowest part of the skirt. So I have no idea what to tell my machinist to do.

Hopefully SteveC will be near a computer and can chime in.

Thanks,

Rob
 
rjplenter said:
They are meant for an "87mm" bore, but they measure 86.55mm across the crown, 86.8mm half way down, and 87mm at the lowest part of the skirt. So I have no idea what to tell my machinist to do.
Click to expand...

"Piston fit in bore" is on page 10-2 of the link JimD posted, fifth up from the bottom. That's the part that really matters.

The first entry on that page tells you how to measure the piston diameter, although your measurements will be .6 mm higher because you're working with 87 mm pistons instead of 86.4.

Warning: Although 100% of the motors I've built are still going strong, that's a sample size of one. So if anyone who has built more than one of these motors tells you different... Listen to them not me.
 
Well Mondial are OE pistons, so go with the OE spec.

Measure the piston accurately (or have your machinist do it) and add 0.03 to 0.05 mm for clearance.

Piston is measured at right angles to the pin, about 25mm up from the skirt... most pistons are not round, or the same size at the top / middle / bottom.

Some manufacturers make the pistons bore size less clearance (like Mahle) so an 87 piston isn't 87.0 at all... it's 86.96, and the bore should be exactly 87.00 for precise clearance ... not sure about the Mondials you have.

Your going to need to skim the piston crown, and remachine the inlet flycut as well... as 34.45CH will poke past the top of the block a bit too much with a 67.4 crank and std rods.... but figure that out once you have the block bored and decked for flat.

BTW it's going to be closer to 1603cc when done... ;-)

SteveC
 
My packet of Mondial pistons say's Mahle Mondial, I think that Mondial is/was a part of Mahle company.

I believe that Mondial 87mm pistons are fo 87mm bore.
 
It is nowdays... but never used to be.

Mahle bought AE (Borgo) and Mondial back in the late 90's early 00's ...

the Mahle's I sold Hussien were German made Mahle in a red box and marked made in Germany... before they bought Mondial (Mahle-mondial will be a Green box) and are Italian manufacture ...

Though I have bought mahle packaged Mondials too... box made in germany, pistons made in Italy, repackaged into Mahle (red) boxes possibly due to production shortages...

Just like I've had Kolben Schmidt pistons repackaged in (red) mahle boxes...

Real German made Mahle and German made Kolben Schmidt's are generally lighter weight... hussiens 0872 mahles (which were repackaged Kolben Schmidts) were about 25/30 grams each lighter than PeteX19's equivalent Mondials (same as Rob bought) ... and have a dull grey appeaarance due to some sort of phospated coating ... the Mondial's and Borgo's are bright shiney alloy.

SteveC
 
Mine came in a brown box

The box is marked "Mondial" and everything on the label is in Italian. But that's just the box of course.

Thanks Steve, I left a piston (I measured them to be all the same) with the machine shop so I will call them this morning and recommend 0.03-5mm.

Like others here we have a long way to go. I'll be getting one part machined at a time as needed with trial assemblies and careful measurements in between.

Cheers,

Rob

p.s. yes. roughly 1602cc. My Aussie mates said, "So you are not sticking under the 1600 class?" hahahahaha They've been hanging around CAMS events for toooooo long! :shh:
 
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BE CAREFUL

Different piston types have different clearances. Cast pistons have very close clearances, close to the stock Fiat manual settings. Forged pistons have much larger clearances, up to .005 depending on the design and use. Normally asperated motors can use closer clearances than blown motors. You really need the manufactures info.

Good luck
Charlie
 
These pistons are cast

I left a copy of the factory specs and the other 3 (they're all numbered for their cylinder * ) pistons with my guy this morning. He was very appreciative saying now he can carefully match each piston with each bore.

He said that 0.03-0.05mm clearance was tight but not unheard of. Then he muttered something about 'mercan V8s and he was sick of them and will really enjoy this job.

I hear what you're saying Charlie, but unfortunately there is no website for Mondial, and Mahle and KS websites just say how good they are. And the data sheets I have found...



...don't offer much. Column 8 simply says 87,00 in this case. If measured where indicated by Fiat, mine are 87mm minus 0.03mm so I think we are good.

* They are numbered because I matched them (and their pins and clips) to individual rods (with bearings) to be equal in weight to less than 1 gram. Excessive? Probably. But I have an accurate electronic scale and my scientist side said "Do it!". Also, one of my fathers favourite sayings was; "Do it properly or not at all.".

Cheers,

Rob
 
It certainly cant hurt to match weights... I always do it..

Same with hone to the size of each piston, that's how I get my machine guy to do it... pistons numbered with felt tip on top...

what was the bare piston weight? (no rings/clips/pin)

Brown box/ white sticker/ greeen circular seal label on top... 1990/1980 production, Italian made. But perfect condition NOS so age makes no diference.

SteveC
 
GREAT RGPLENTER

.003MM IS A BIT TIGHT FOR OLDER MOTORS BUT ACTUALLY QUITE COMMON WITH NEWER ENGINES. .005MM IS PROBABLY CLOSER TO WHAT YOU WANT. AT ANY RATE YOUR IN THE BALL PARK. HOPE IT ALL WOTKS OUT OK.

GOOD LUCK
CHARLIE
 
Bare weight

is 438 grams. Not the lightest pistons out there, but they have a full skirt.



Which means they should be pretty stable in the bores. Even with the ever so slightly shorter Scat rods they will probably need a tiny amount taken off the top and obviously those valve recesses are way too small. So those mods will reduce the weight a little. Which of course means I'll have to balance the weights again before installing...

The full skirt also means the pins are long and I will see if I can get them taper bored. This is the first time I have used this machinist so I am keen to see the quality of his work on the block before I throw lots of parts at him.
 
Clearance

Over 30 years ago I purchased a set of 11.5 :1 pistons, 87MM bore from Al Constantino in Florida. Clearance for the pistons was .025" to .004". I took the smaller clearance and it was a mistake. These little engines get really hot back there and after a hard run on a hot day starting the engine was difficult. The pistons due to heat soak were jamming in the bores.

New engines are way different than these old engines. With variable cam timing at Idle they produce 30 HP with very little pumping loses. They will never over heat in a traffic jam. Upping the compression and changing the duration of the cam timing all produce more heat, which causes the pistons to expand more. This is old technology. Keep this in mind, forget about today's engines and think like 30 years ago.

TonyK.

Grimsby Ontario Canada.
 
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Please don't take offence by my questioning but, are you sure about the weight of a single piston?

It appears that I purchased the exact same Mondial pistons from the same seller in Greece off of Ebay although mine are 86.8mm. One of my single pistons weigh 603g each with the rings and wrist pin installed as they were shipped.

165grams lighter is a little unbelievable.

http://www.ebay.com/itm/26120880440...op=1&_dmd=1&_ipg=200&_nkw=261208804402&_rdc=1

Mondial piston from Greece


Scat H beam rod



Original Mahle piston from Germany with Scat H beam rod, this is "Lookforjoe's" setup. These pistons are slightly lighter then my Mondials at 570g.


'PeteX1/9
 
Mine range from 610 to 612 grams

with rings, pin and spring clips. Steve asked for bare weight. "what was the bare piston weight? (no rings/clips/pin)"

So our pistons are almost the same weight.

Cheers,

Rob
 
I did read "bare weight" on your post but I didn't realize that the pin, rings and clip weighed 170grams. Wow I guess a lot of weight reduction could have been achieved having sourced lighter pins. Steve did mention this fact. I never had a chance to weigh my pins as they were already installed when I handed them over to the machine shop.

Good Luck,
'PeteX1/9
 
No worries Pete

I just weighed my pins at 132 grams. There is no way to lighten the spring clips or the rings, so the pin is the only option.

I also measured them:
Length 68.98mm / 2.716"
OD 22.02mm / 0.867"
ID 13.00mm / 0.512"
Wall thickness 4.50mm / 0.178"

The options are to have them taper bored or to find after market alternatives. A 2 minute search turned up these from Summit Racing:

http://www.summitracing.com/parts/ros-866-01-27/overview/

I believe SteveC wrote about these previously. They are 100 grams and at $17.99 each may be cheaper than having the OEMs machined. That's a 24% reduction in weight, pretty significant. My only question would be, is "aircraft-quality chromoly" good enough quality? That term aircraft-quality is bandied around a lot and is not necessarily that great.

Cheers,

Rob
 
If you bore your cylinder 87 will not mistake but to make easy for engine 87,02 will be better and easier for engine .
All Mahle , Mondial is grupacion can be find different pistons in different packing ...
 
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