Finding Pistons??????

[randiego]

Hey all,

I recently pulled the trigger on rebuilding my 78 (California) 124 Spider. It was time and after tear down, found that it was good that I decided to do so as my rod journals were starting to loose metal Had I run a little longer, I would have spun a journal and who knows what else??? I am thankful that I got away with my crank being polished only and not needing to be cut, hence STANDARD bearings. Anyway, I was rounding up the parts and talked to a parts supplier back East. He sold me "performance" pistons. Not thinking anything out of the ordinary (I assumed that they were performance in shorter skirts or lighter weight etc. I was in a hurry and was not more inquisitive about them) When I got them, I found that they were high domed pistons with recesses for the valves.

Now, if you know our fuel out here in Calif. we have at very best (on a good day) 91 octane at the pump for premium fuel.
These "performance" pistons turned out to be 10.5 to 1 compression pistons. This would require me to burn 100 octane fuel (which we have at two or three locations here and at a premiuim price at over $7.00 gallon), or use a fuel booster. This is NOT what I wanted. I want this engine to be restored to OEM specs for 78 and my pistons that came out were flat, not domed.

I called the salesman, back and discussed this with them, not realizing their performance pistons were high compression pistons. He tried to tell me that using a "colder" plug would take care of the pre-detonation issue. ? ? My machinist laughed. He told me the only way that these pistons would work would be for me to retard the timing to the point that I would loose a lot of horsepower. or we could machine the tops of the pistons down, but this would negate the warranty on them. Un-acceptable.

Turns out that the reason for the salesman selling me these pistons was......those were the only ones that he had in stock. His cock-a-mamie story about a cool plug was his attempt for me to keep the pistons. Any one knows that it is a LOT of work to dissasemble an engine to repalce pistons that won't work.

I have called to the other supplier on the East Coast for stock 6MM over pistons and they do not have any. Here I sit with my engine halted in the rebuild process trying to find stock pistons for my 1800 engine. DO any of you out there have a source for (6mm over) stock pistons formy rebuilder? Any assistance in this matter will be appreciated. You can contact me directly at (760) 754-3166 (office) or my cell (760) 533-7540. Email: rklockent@sbcglobal.net Thanks, Randy

[ventura ace]

Randy,
I'm not sure what pistons you received: 8mm dome, 6mm, 4.5mm, or other?? The piston itself is only part of the equation for calculating the compression ratio. If they are 8mm or 6mm domed, I believe I'd be concerned that the CR may be too high, but if they are 4.5mm dome or less, you may have a good combination. You'll need to do some accurate measurements of the combustion volume in the head (typically about 49cc's for a stock 1.8L head that hasn't been decked), the deck height of the block, the head gasket thickness, etc. to get an accurate number on the CR.

BTW, I believe that you mean 0.6mm oversize, rather than 6mm oversize.

Here is a link to a 4.5mm domed, 0.6mm oversize piston offered by AutoRicambi:

http://www.autoricambi.us/cgi/commerce. ... =EN7-406-Z


Alvon

[lanciahf]

Randy,

You might have another option. I've read where some owners with 8mm dome pistons have had about 2 to 3 mm shaved from the top of the pistons.

Might be enough to get by?

[vandor]

Randy,

You might have another option. I've read where some owners with 8mm dome pistons have had about 2 to 3 mm shaved from the top of the pistons.

If they are the 8mm dome pistons then the actual CR would be more like 10.8:1-11:1 (it was over 11:1 in an engine I built), so shaving 2-3mm would not do that much. You'd have to shave ~4mm, but since the domes are hollow, that would only leave you with half the original dome thickness. I am not sure if that would be reliable in the long run, and I think few people would be willing to take the gamble.

[maytag]

I absolutely concur with the above posts. you need to know exactly what your cr will be before just summarily chickin' those pistons.
I see no reason you can't live with a 10.5:1 cr on the street, with 91 octane pump-gas. yes, you'll retard the timing just a bit. this will develop less power. BUT: less power as compared to the same motor running higher octane fuel with more advance. NOT as compared to your stocker. you would no doubt be quite happy with the motor, if 10.5:1 is accurate. but you can't guess based on what they told you. Your machinist should be able to do the math for you and tell you exactly what you can expect, if he is competent. (don;t ask him to do it for free: he'll just guess). but if your maqchinist is telling you that you can't run 10.5:1 on 91 pump-gas, you may need a new machinist.

[narfire]

I thought IAP had the Mahle pistons that were flat top and 9 something CR. They were .4 over,requiring re-boring at a machine shop. I have a set in my FI and they seem just fine. (3 years ago) You were looking for stock pistons(84mm) or pistons .6mm oversize (84.6mm)? I'd be guessing anything oversize no longer becomes stock and you will require machining(to fit new diameter) for the new pistons. Here that cost between $60.00 and $80.00 a hole (4) Perhaps you might want to source 84mm pistons or if your bore is "slightly" worn a set of oversize rings with your current stock pistons might be what you are looking for.
If $$$ permit,do try and get the whole works properly balanced and shave the flywheel as well.
Chris

[124JOE]

hey guys what would a thicker head gasket do for him?
do they make them?

[ventura ace]

The 2mm thick head gasket that Guy Croft sells will lower the CR about .5, as compared to the standard 1.3 mm thick head gasket (assuming the CR is in the 10 range). That is exactly what I did for my engine (8mm dome pistons) to lower the CR from 10.6 down to 10.1.

Alvon

[124ADDHE]

So there you go, thick, high quality head gaket, keep your pistons and your spider will put a big smile on your face when ever you give it gas + your fuel economy will improve after shes broken in. bonus bonus

[So Cal Mark]

The piston situation isn't the best these days. We had Ross make a mold for us for forged pistons so that we can dictate the dome height. It can go from a flat top to whatever dome we ask for. it's great piston and very strong and uses a standard ring pack rather than a unique set for Fiat-only. And uses a pin retainer that isn't so darn difficult to change. The only problems are lead-time (4 weeks) and cost. A set with rings is in the $600 range, but they are forged rather than cast.

[Fiatmonkey]

I am not sure I follow the problem. First, I doubt very much a vendor would sell something that just simply doesn't work. Second, aren't there countless cars now on the road running 10:1 and higher compression? So what's the big deal if the vendor gave you a proper way to eliminate any problems. Then why not listen to them? It's been my experience with most of the vendors that they know more about my car than me or my mechanic.

[vandor]

I see no reason you can't live with a 10.5:1 cr on the street, with 91 octane pump-gas.

Dunno about that... I have a true 9.8:1 CR, run 93 octane gas (widely available in Texas), and the engine still pings sometimes. Static advance is ~11 degrees, and the car has the later distributor with only 22 degrees of mechanical advance.

More compression with less octane sounds like trouble.

[vandor]

>I am not sure I follow the problem. First, I doubt very much a vendor would sell something that just simply doesn't work.

You are such an optimist
I know a vendor sold these 8mm dome pistons to a customer along with a 1800 head to put on his 2000cc engine, so the guy had over 11:5 CR!
Another told the owner of a Turbo Spider that his car came from the factory with special low-compression pistons (BS). I could go on... Most vendors are very good, but every now and then you come across someone just trying to sell you something. It never hurts to get a second opinion.

>Second, aren't there countless cars now on the road running 10:1 and higher compression?

Yes, with knock sensors and constant computer control of fuel and spark. Not the same as the ADFA carb

[maytag]

I see no reason you can't live with a 10.5:1 cr on the street, with 91 octane pump-gas.

Dunno about that... I have a true 9.8:1 CR, run 93 octane gas (widely available in Texas), and the engine still pings sometimes. Static advance is ~11 degrees, and the car has the later distributor with only 22 degrees of mechanical advance.

More compression with less octane sounds like trouble.

Csaba:
of course I value and respect your opinion. But if we review what the octane does for you, you can do the same with advance / retard. Simply put: Octane delays combustion. The higher the octane rating of the fuel, the more it will resist combustion, allowing higher cylinder pressure to develop before it ignites spontaneously (without a spark). If you delay that spark so that combustion (without the inhibitors of higher octane) happens at the same relative timing, then you still get fantastic cylinder pressures, and avoid the dreaded knock.
This is precisely why so frequently you will find motors which actually develop LESS HP with higher octane fuel. No, not the "norm", but a motor in a high state of tune will develop less power with more octane, all other factors being equal.
At my high altitude, we frequently have to get creative in the advance / spark plug temp combinations for any given CR. That's why the "quench" area (or "squish", as some call it) is so vital on motors up here too. Because we need that flam-front to travel as fast as it can, once it has actually been ignited.