Piston to Block specification

[tgoodrick]

Hello all,

Rebuilding an engine and the engineer has asked me if after honing the bores if a total of 4 thou clearance was OK between the piston and the bore??

Your responces would be appreciated as he requires an answer soon!

Thanks in advance.
Troy

[cthargiss]

Troy, It all depends on the engine you are rebuilding. For instance, a 1.3L TC street engine uses .0023-.0031 in. while a 2L TC uses .0019-.0027. and 1.4L TC is .0027-.0035. Race engines on the other hand can vary from .004 to .015 depending on application . High pressure forced induction engines burning Nitromethane have been known to go as high as .020. In order to be exact I would need to know; engine type and size, bore size, piston type (forged or cast, cylindrical or cam ground) , compression ratio, induction type, camshaft specifications, Ring type and number of rings, RPM limit, and piston alloy type. All of these influence the clearance needed to have an engine that will perform for the purpose that you intend it . Hope this helps.
Craig

[Will]

4 thou is absolutely dandy, should be fine.
In fact, you can go a little looser on the 2L and still be within factory spec. If your rings were pre-gapped for the smaller bore, you may need a new set, but otherwise, you shouldn't have any worries. This tolerance tends to close up when hot anyway, and the thrust offset seems to do a pretty good job of keeping the skirts smooth- how many of us have ever seen a scuffed one?

-Will

[Will]

What the?!
1.3L TC? 1.4L TC? WHAT is he talking about???

-Will
BTW: 1.8L uses 3~5 thou. ; 2L uses 4~5 thou total clearance.

[DJ]

I've seen references to these engines a few times before and they always seem to have been referring to European engines. I didn't think they were TCs, though.

DJ

[rossocorsa]

there were several sizes of twin cam over the years 1297,1366,1438,1585,1592,1756,1995

[Will]

That's sure a new one to me- the smallest TC I know of is the 1592.
1592, 1608, 1756, 1995.
The 1297 is the little Berlinas, but i thought the 1297,1348, and 1585 are all SOHC engines! AREN'T THEY?????

SOHC: 817, 843, 903, 1116, 1290, 1297, 1438
is this not correct??

[Will]

Also...Craig's numbers don't match Chilton's for the 1297 or 1438, or Lancia's (Fiat's) for the 1.8 or 2L, so I'm wondereing what he's talking about?
He could be talking about Honda motors for all I know, but those aren't the correct specs for Lancias/FIATs AFAIK!
-Will

[rossocorsa]

the beta was always fitted with tc engines, never single cam, the twin cam originated as a 1438 in the early fiat 124 sport coupé and was later expanded to 1592 then 1756. the range was later rationalised to reduce the number of components that made up the different sizes leading to 1297 (replacing the 1438 in the beta berlina and coupé) 1585 (replacing 1592) and the 1995. the 1366 was a later variation fitted to FL2 1300 coupés

[tgoodrick]

Let me shed some light :idea: on the engine.

It's a 2.0Lt with standard 84.0mm 9.45:1 pistons.

Block has 2 thou difference from top to bottom.

4 thou overall clearance after honing from block to piston.

Regards Troy

PS I'm next going to linish and balance the crank, has anybody done this before, if so what else should be balanced with the crank??

[Will]

Flywheel should be balanced with the crank.
(IMHO)
-Will
Early 124's are OHV engines on this side of the pond, I certainly wasn't aware that FIAT made them TC's on the other side. Possible though, I guess.

[DJ]

Front crank pulley and clutch assembly too, no?

I've heard the pulley can be quite "off" sometimes.

[Will]

Tryiing to delete this double post...

[cthargiss]

Will, the numbers come directly from Lancia, and are duplicated in the Haynes manual on Betas. Lancia made a lot of things for the european markets that we in the US never even suspected. Craig

[Will]

OMG! WHOOPS!!! :oops:
Can't believe I did this, but looking at the spec diagram, I misread it, the diagram shows a piston in the bore with the clearance indicated on one side, I had assumed it was EITHER side, but it is drawn as ONE side (total clearance), consequently I am DOUBLE the recommended clearance for what I posted SORRY GUYS!!!
This is my second time "falling asleep at the wheel" in a week, the pranksters on the Scorpion list played a VERY emabarassing prank on me a few days ago that went totally un-noticed.
Apologies, Craig, your numbers now make sense, with the exception that going from metric to inches always contains an error, and the Haynes people use mmx.04, so they are alwaya a little off. (note: inches to metric is exact at 25.4mm/in)
CORRECTED NUMBERS AS FOLLOWS:
2L: Clearance (total) should be ~.0020"-.0029"
However, this is a factory motor, and the hotter the motor, the bigger the clearance should be. I think Mr. Goodrick is OK with the .004" he has, I would certainly run that rather than acquiring oversize slugs and reboring the cylinders.
Craig; Sorry again, my mistake on the interpretation.
-Will

[Will]

OMG! WHOOPS!!! :oops:
Can't believe I did this, but looking at the spec diagram, I misread it, the diagram shows a piston in the bore with the clearance indicated on one side, I had assumed it was EITHER side, but it is drawn as ONE side (total clearance), consequently I am DOUBLE the recommended clearance for what I posted SORRY GUYS!!!
This is my second time "falling asleep at the wheel" in a week, the pranksters on the Scorpion list played a VERY emabarassing prank on me a few days ago that went totally un-noticed.
Apologies, Craig, your numbers now make sense, with the exception that going from metric to inches always contains an error, and the Haynes people use mmx.04, so they are alwaya a little off. (note: inches to metric is exact at 25.4mm/in)
CORRECTED NUMBERS AS FOLLOWS:
2L: Clearance (total) should be ~.0020"-.0029"
However, this is a factory motor, and the hotter the motor, the bigger the clearance should be. I think Mr. Goodrick is OK with the .004" he has, I would certainly run that rather than acquiring oversize slugs and reboring the cylinders.
Craig; Sorry again, my mistake on the interpretation.
-Will

[cthargiss]

No sweat Will, The piont I was trying to make is that Lancia specifies .00196-.00275 for the factory 9.8 CR 1800cc, so .004 might be a little excessive for a street car that is not continually driven at high piston pressure and temperature. Daily driving with this much clearance will lead to premature bore and ring wear, resulting in blow-by and oil consumplion in less than 20K miles. Sorry if I was obscure in my earlier postings.
Craig

[Ken H]

Block has 2 thou difference from top to bottom.



This number alone would point to the need for a rebore, as significant, uneven wear has occured. Honing and new rings could stretch the life a bit longer, which might be OK if there are no long term plans for the engine (i.e. it then becomes someone else's problem!).

- Ken

[Graeme Wellington]

>PS I'm next going to linish and balance the crank, has anybody done this before, if so what else should be balanced with the crank??

I trust you mean to linish the crank journals. To do the whole crank would be totally un-necessary and a waste of $$$. Lancia 2 litre cranks are super-strong. When balanced they will take just about any punishment you can throw at them. My Lancias are standard, but my Fiat Abarth 124 Rally is running a worked 2 litre. I've got it rev limited at 8000 because of design limitations in the main journals and rods - and often bounce it off the limiter. The motor is super reliable, has a balanced bottom end (crank, flywheel, pulley, clutch), rods are end-to-end balanced, lightened and shot-peened, and pistons are forged, balanced, run 4 thou clearance (bit rattly whilst warming up, but suited to the application).

Polishing the crank can add strength, but if the polished surface is then scratched or nicked it will be significantly weakened because of the stress concentrator that the scratch or nick becomes.

My current project is an X1/9 Abarth prototipo replica with Lancia Beta engine and transaxle. It will run a sprintex screw type supercharger, efi, intercooling etc. with a target output of 300 bhp at the flywheel.

Graeme Wellington

[CorseChris]

Flywheel should be balanced with the crank.
(IMHO)
-Will
Early 124's are OHV engines on this side of the pond, I certainly wasn't aware that FIAT made them TC's on the other side. Possible though, I guess.

My first exposure to the TC was in a FIAT 124AC Coupe 1438cc. Sweet little motor...until the oil pump drive shaft snapped.

...and on the balance front, just had one done. Crank, flywheel, front pulley, clutch coverplate, rods (with shells), pistons (with rings, pins & clips). Clutch cover was the worst item, flywheel next. Crank was pretty close to start with.

Didn't solve the vibration problem though :( (see elsewhere!)

[arc]

I can't believe some of you guys didn't know about the smaller capacity twin cams for Lancia in Europe. You know they had their special local models, the same as you may have much closer to home. Jeremy.

[Will]

Well, in defense of those of us in the USA; Unless you speak Italian, you probably wouldn't ever hear of one of them. The reason for this is that they were never shipped here, English documentation is practiacally nonexistant, and they aren't suitable donors for the sizes of cars we have here. There are no microcars in the US. Sure, you'll find a few 500's, 600's, 750's people brought over, but the next thing up is a (SOHC) 1300 or 1500 X-1/9 or 124 Spider 1800.
There's a 1438 TC special sedan and wagon according to the Haynes manual IIRC, but I've sure never laid eyes on one!

[snoozin]

I can't believe some of you guys didn't know about the smaller capacity twin cams for Lancia in Europe.
A while ago I picked up a copy of "Twin Cam Italia" by Phil Ward w/ Brian Long from pitstop.net in Western Australia because i was interested in history and applications of the lampredi... very detailed book, may be of interest to ppl here.

link (from pitstop) to book: http://www.pitstop.net.au/pitstop/prog/OpenDocument.cgi?id=V0X7S13PUM&PLU=12598

(damn, price has gone up in the last year, i thnk..)

[arc]

Will, they haven't hit our shores here in Australia either- to my knowledge. But I thought most people on this forum would have encountered literature on these models eg. service manual. Or aren't they mentioned in your manuals?? Anyway, it's probably a good thing, the 1300 is pretty gutless (83 hp).
Jeremy.

[omicron]

Still compares well against modern 1.3-1.4 litre engines which have 25 - 30 years further development.

Andrew