Some pics of 308 bottom end after 100k and piston check

That bearing doesn't look too bad, considering.

Plastigage?

Mike the crank journals, check for out of round?

 

When you say 3K, you are saying just parts ? Or are you including labor ? What type of hours would be needed for such on the 308 rebuild.

Thanks.

 

k...so to do it from top to bottom then how many would you say ?

(Just figuring out a budget, thanks).

 

How positive are you of the mileage, or if the motor ever had previous work or not? I have long suspected these motors were built to a very high standard, and should wear on at least as equal footing as any Mercedes. If this is in fact a bonified 100K mile engine thats never been apart, then it would appear many of these cars could have 10 times or more miles than they indicate.

I have .0025" wear in the tops of my liners, and looking at the bottom side tonight, I found number 3 and number 6 rods are non original, so its been apart at least once in its past. The connecting rods are stamped with the cylinder number. 3 and 6 have not stamped, just a hand engraved number ground in where the stamp would have been.

And this car didnt even have split seat bolsters or worn carpets. Hmmmmmmm. That REALLY makes you question the ratty cars, eh?

 

OWM shows standard bore nominal size 81.000 to 81.020mm (3.1889 to 3.1897"). Going around with a bore gauge I'm getting 81.064mm, or about 3.1915 just about everywhere, cylinder to cylinder and at 90 degrees either direction. There doesnt really appear to be much of a ridge, but all the hone marks are gone except the very bottoms of the cylinders. Im going to try sneaking the gauge in the bottom and try to read the original bore size before I do anything silly. The measurments seem far too consistent to believe it would wear that much.

So your not really sure of actual mileage, just taking a wild stab in the dark based on valve wear? I dont know as I would compare valve wear with other engines. The way these buggers spin up valve wear is probably 50% faster than on just about anything else.

Mine is "indicating" 44K, but the oil was pretty black when I found her, and even after 4 oil changes in 2K miles it was still making the oil black, and there is some light sludge on the oil baffles. Thats the trouble with a 30 year old machine, you just wont ever know, even with a pile of records.

91tr did a top end overhaul on a 308 many years ago with 100K on it. Maybe he will recall how much wear he seen.

 

I was going to try slipping the bore gauge in the bottom and try to measure the bottom of the liner where the rings never run, but I think the rods are going to be in the way. I will also try slipping a feeler gauge up past the skirt to get some idea of piston clearance.

 

Let me preface by saying that I've never built a 308 engine, but it's not that different from other alloy block/head engines like Alfa Romeo, for instance.

Am I to understand that the factory honed the cyilinders only after putting them into the block and with a tq plate in place? Seems unlikely. What causes the distortion?
Or is it the case, that the cylinders get distorted due to use (apart from wear by the piston/rings), and need to be made round when re-used?

It'd be great to see some measurements of cylinders taken in situ and the same cylinders out of the block, and also the distortion of the block itself. If the sleeves distort, no problem, but if the block itself causes a certain degree of distortion, that will also have an effect if new sleeves are put in.

Some insight would be appreciated!

 

The OWM speaks about the liners, that they should be removed for regrinding, but its prefered they be replaced. It seems many prefer to bore them in the block with torque plates, and there was just a thread posted within the last few days giving some mesurements before and after the liner was subjected to torque pressure. On the face of it it would appear to offer some advantage, but its still an entirely unknown aspect.

Boring a block with torque plates was known long before the 308 came along, but was used primarily on cast iron blocks with stationary cylinders that dont move around. One would have a hard time to imagine Ferrari didnt have a good reason to request removing the liners for boring. My feelings are that the engines are rather plastic, and flex, twist and bend during heating and cooling cycles. The fact is that the physical dimensions of the engine are always in a state of flux, always moving. Perhaps the liner would retain a more overall cylindrical shape during its lifetime being turned round on a jig outside the engine, than if it were bored in an distorted process? Who knows?

Personally I trust Ferrari knew what they were doing, and am likely to stick with their procedure until or unless I am fully convinced otherwise. The amount the liner was off under torque, about .001" doesnt bother me, simply because once its hot it could just as well be something else, and something else again tomorrow in a different direction. The piston has clearance in the bore when running, so unless we were talking several thousanths of change I dont see it being of any great effect one way or the other. But I am also willing to be enlightened if there is valuable evidence to support a change.

 

Paul,

Fully agreed on the plasticity of the block, hence my question: if it were the block itself causing the distortion of the sleeves, it would do the same thing regardless of reground sleeves (out of the block) or putting new sleeves into the same block.

However, the plasticity of the block and things changing shape due to the cycles it is exposed to should, in this case, be rather minimal, or we would read tales about broken cranks and camshafts.

I think I'd be quite happy to work the sleeves out of the block, in fact, I think I'd prefer to do so; it is much easier to correctly prosition a sleeve for machining than it is to do so with a block.

 

I have no experience rebuilding 308 engines, but quite a bit rebuilding Porsche 911 engines. On those it is quite common to find that cylinders and piston to cylinder bore clearances are still acceptable (within tolerance) for high mileage motors, but often the ring land gap (vertical gap between the thickness of the ring and the ring groove hieght in the piston) is worn to unacceptable levels. (from memory 002" is new and 007" is worn out).

This slop of the ring (usually top ring) causes the ring to slap back and forth every time the pistom changes direction, and often causes the ring to break.

Interestingly I dont read about these ring land gaps in piston/cylinder discussions of 308 motors. Does this mean that ring land gaps are not a wear point for 308 motors??
Martin

 

once before I rebuilt my 308 2 valve I forced nitrous through the motor until I ran out of jets! It never blew up and basically could have run forever. There was no bottom end wear.

 

To score all your cylinders like that, IMHO one of three things, or all, happened. Either piston to cylinder clearance was too tight, the engine siezed or ran dry in the cylinders, or debris got into the engine. Some of those scratches look pretty severe. The first big motor I ever built, I put together a bored 400 Pontiac when I was 17. The motor had maybe 10K on it when I decided to put a three duece carb setup on it, and in the doing, dropped a 5/16" washer down the #2 intake port. I spent two days trying to fish it out and gave up. Then like an idiot I thought if I started it it would "blow" it out. I actually drove it back home about 10 miles with that washer in there. When I pulled the heads, there was only one light score on the cylinder, the rest, all other 7 were wearing in beautifully. Actually the washer was still in there, imbedded in the edge of the piston and trying to score the cylinder. But to be honest, your scoring marks look just about as bad as what that washer did. Something definetly went wrong somewhere.