V1 Rod change question. Clearance between crank and rod

[mike_sno]

Hi all,

Talked to a very experienced engine mechanic, but no experience with ecotec about the rod and piston swap.

Regarding the rods he mentioned that the rod to crank connection have to have a certain clearance and if not need to be machined to fit together. What's your opinion on doing that?

Secondly, I think it would be possible to swap the rods with just removing the oil pan. The screws should be accessible, right?

 

[Ross]

Use some plastigage, and check if you have the proper clearance at the connecting rods big end.

The bolts on the big end of the connecting rods are accessible, but replacing the connecting rods thru the oil pan will require removing the crankshaft girdle (the 3" of cast aluminum that the oil pan bolts to), then the crankshaft, then pull the pistons.

You should check/modify your ring gap too. The rings will need more gap if you are running more boost than stock... otherwise your engine could seize up.

I'm not sure which ecotec you have but you could Mod your signature here to let us know.

 

[mike_sno]

Thanks, sorry I wasn't quite clear, i was thinking of removing the oil pan to access the screws of the rods from the bottom. Remove the valve assembly and get the pistons out to the top.

Where do I get the clearance information from? Is there a good engine manual?

I'll update my signature as soon as I receive the goblin. I believe so far it's a LAP 2.2L engine.

 

[Ross]

AllDataDIY Login has the specs for the LSJ engine... I don't have access to the LAP engine specs.

Connecting Rod Bearing Clearance 0.029-0.069 mm (0.0011-0.0027 inch)

Crankshaft
Connecting Rod Journal Diameter 49.000-49.014 mm (1.9291-1.9297 inch)
Crankshaft End Play 0.050-0.380 mm (0.0012-0.0150 inch)
Crankshaft Main Bearing Clearance 0.031-0.067 mm (0.0012-0.0026 inch)
Crankshaft Main Journal Diameter 55.994-56.008 mm
Connecting Rod Journal Diameter 49.000-49.014 mm (1.9291-1.9297 inch)
Crankshaft End Play 0.050-0.380 mm (0.0012-0.0150 inch)
Crankshaft Main Bearing Clearance 0.031-0.067 mm (0.0012-0.0026 inch)
Crankshaft Main Journal Diameter 55.994-56.008 mm

Connecting Rod Bolts
^ First Pass 25 Nm (18 ft. lbs.)
^ Final Pass 100 degrees
Connecting Rod
Connecting Rod Bore Diameter - Bearing End 52.118-52.134 mm (2.0519-2.05252 inch)
Connecting Rod Bore Diameter - Pin End 20.007-20.021 mm (0.7877-0.7882 inch)
Connecting Rod Side Clearance 0.070-0.370 mm (0.0028-0.0146 inch)
Connecting Rod Straightness - Bend - Maximum 0.021 mm (0.0083 inch)
Connecting Rod Straightness - Twist - Maximum 0.04 mm (0.0157 inch)
Crankshaft
Connecting Rod Journal Diameter 49.000-49.014 mm (1.9291-1.9297 inch)

 

[mike_sno]

Thanks! That's awesome. I did not know this side!! How likely is it that the clearance is not correct and the rods/bearings/crankshaft have to be remachined? I think that would be an expensive adventure...

 

[Ross]

Probably the clearance is good, but plastigage is cheap insurance, and nobody likes a seized engine.

 

[mike_sno]

Yeah, the problem is just, once I spent the money for pistons and rods and find out that the clearance is not ok, this route of getting more HP is not making financial sense. I wonder why I have not seen any of the YouTuber doing this… If they all don‘t care?

 

[Gtstorey]

Engines are not Lego's. You can't just swap parts without measuring things. I would want to check piston to valve clearance with a rod change. And I would also be a little concerned about a compression change if I couldn't measure the rods to confirm length.

 

[mike_sno]

Yeah it's just not as easy as it looks in the first place. And the other options like new donor and engine swap are not to expensive

 

[Desert Sasqwatch]

If your wanting to build a higher HP engine, it IS highly recommended that it is out of the car so all the critical measurements can be made and you have the 'elbow room' to build it the right way. AND it typically is not cheap, a 300 HP TC is mostly tuning. Higher HP TC builds require pistons at a minimum and doing engine dynamic balancing (not balance shafts) and blueprinting becomes a must as the HP target goes up. Do it right the first time and put the time in to make certain it all measurements match up to specs for engine longevity.