Can I use vin M pistons in a vin J 3100 ?

[mongo]

I bought a builder engine from a guy (GM mechanic) who assured me it was a vin M. I had the machine work done (Bore, hone, heads... the whole bit) and bought a complete rebuild kit (pisons, rings, bearings, cam, etc.

I am just finishing up putting the top end on the engine this morning and the intake gaskets won't line up. So I started digging around at the other parts that were included with the motor and see that it was NOT a vin M but actually a vin J.

Does anyone know off hand:

Will the vin M pistons cause a valve clearance or compression issue?
Will the will the main or rod bearings cause a problem?
Will the cam be a problem?
Will the thicker cam chain cause a clearance issue?

Like I said, it was almost completely together when I noticed I had the small port intake....

[mongo]

To add some perspective:

I have a 98 Buick Century in the driveway with a broken cam. I bought the other motor (being told it was the same) to build on the stand and just do a one weekend engine swap to make things nice and easy...

I have two engines to work with... I just want to get this car going with the least amount of additional expense and hassle....

[3400-95-Modified]

Vin M bottom end is the same as the Vin J... You just need the appropriate small port lower and upper intake gasket sets.

No issue with the cam, or chains... If you've looked on this forum you would see many recommending the older Vin M style chain due to it being a bit tougher than the 2000+ counterpart.

[mongo]

Sweet!

Yeah... that chain is at least TWICE as beefy as the vin J chain. I just didn't know if I needed to use the other motor's timing cover to add clearance.

So... No problem that I rebuilt a vin J engine with vin M parts.... and torque specs...

What is the actual difference in the two motors then? The only things I could find was the intake, camshaft and pistons (both related to valve duration, compression, and clearance). No other part differences?

[3400-95-Modified]

The main differences are the heads and intake... Small port is Vin M aka L82 and large port is Vin J LG8... Yes intake valve is a tiny bit larger but not much... but the ports on the intakes themselves are completely different.

The only difference you may see in a cam is the sensor ring on it... They both will do the same thing but they changed how they were designed a few times.

Pistons should be exactly the same... If they are not same PN's then it may be due to later ones LG8 having side skirt coating from the factory and L82 ones didnt...

Look at the specs on this site... Bottom end dimensionally identical.

LG8 Specs

L82 Specs

[mongo]

I am not trying to cast doubt on anything you have told me... because it is EXACTLY what I wanted to hear (which is scary)... but I am still curious about those heads.

The pistons between the two engines are slightly different. Most of it I THINK has to do with the depth of the dish since the vin J is around 9:6:1 compression and the vin M is about one point below that. Trouble is that I can't find any clear data that defines that.

When working compression:

You have your volume of the bore and the stroke (the same in both engines so I am good there)
You have the valve timing, lift, and duration (I have a vin M cam but the rockers are vin J but I believe are the same ratio so I SHOULD be good there)
You have the combustion chamber volume (which can be in the piston, head, or both)

The combustion chamber is where I am having a bit of a problem working out. Do you have any insight on that? Was the vin J's extra compression a function of the dish on the piston and valve lift/timing or did the head have something to do with it?

[3400-95-Modified]

The pistons between the two engines are slightly different. Most of it I THINK has to do with the depth of the dish since the vin J is around 9:6:1 compression and the vin M is about one point below that. Trouble is that I can't find any clear data that defines that.

You can't find this info because that is false... Vin M and Vin J were both 9.6 compression. DONT WORRY IT WILL WORK FINE.

A Vin J motor simply put is a Vin M block with a 3400 top end on it and a 3100 labeled upper intake since the displacement is still 3.1L

READ http://en.wikipedia.org/wiki/General...Generation_III

[mongo]

Thank you for clearing this all up! Now I can soldier on with the project!

[3400-95-Modified]

I found TINY differences in the pistons on RockAuto... Not really sure why they are listed differently, Or why aftermarket companies made them differently. Every spec listed on 60* is the same, including cylinder bore and piston to wall clearance.

Sealed Power says 3100 Vin J ones have Recessed Head .270 deep x 2.750 dia, and Vin M are Recessed Head .260 deep x 2.865 dia... But if you look the Vin J is just smaller DIA dish but deeper... vs the larger DIA dish and shallower version of the Vin M... They probably CC damn close to the same which wont change the CR.

Bottom line... Don't worry about it.

[mongo]

Thank you for the wealth of information.

I am ordering the correct gaskets today and hope to install this motor this weekend (weather permitting).

One final question (that doesn't really matter at this point), if the cam lift and duration are the same, why do the parts houses list the cam as unavailable for the vin J ?

[3400-95-Modified]

Because parts houses and parts listings do not know how many things interchange between GM motors. Ben sells aftermarket cams for the 3x00 motor (3100, 3400 and 3500)... The cores are all identical and I believe like the factory replacement one he sells they are based off the 94-99 cam reluctor wheel... There is a photo floating around somewhere of all three cams side by side but I don't remember where it is. The appearance changed but the data it sent from the sensor was the same for each design, as well as the many year sensors all received and sent the same data.

If you look on RockAuto they have a Vin J cam for a 00 Lumina made by Engine Tech PN ES1570... Sealed power only makes a cam that is said to fit the 94-99 motors and they state that because of the reluctor wheel change. Technically Sealed power doesn't even have a listing for a LA1 motor.

SO to sum it up... the reluctor design appearance changed, it's function and whatnot didn't... Aftermarket companies never tested their previous year cams in the newer engines do they don't list them as compatible, but they are.

[mongo]

Woo Hoo! That means I have a spare cam (from the core engine I rebuilt) that I can use in my engine with the broken cam! Once I verify the block is still good..... and replace all the bent valves... and so on...

[3400-95-Modified]

Probably has spun cam bearings... At least I know one I bought with a broken cam did since they ran it too long after it broke without oil pressure.

Here is a pic of a 04 3500 cam and my aftermarket one I was running in my 04 3400 block which would have had the same cam as the 3500. This is all that's different but the leading edge to the left is in the same spot on both cams. That's all that matters.

[mongo]

You are right.... but I just happen to have a spare set of cam bearings sitting on the shelf as well as a small supply of gaskets....

[3400-95-Modified]

Spun cam bearings means spun cam journals aka damaged block... it would need oversized cam bearings and a line bore/hone to fix it. Just something to look at.