Can I use 3400 heads on a 3100 block.

[evartsboy73]

Finally found me a good looking block. Thought it was a 3400 Block until I started to put my new rings on the pistons. It is a 3100 block I assume. Was told it came from a 1997 Lumina. Already have crank in with new main bearings. A little tight to turn but it will turn. Will that be a issue? My main concern is will my 3400 heads work on the 3100 block. I know the head gaskets are different. If the heads will work will everything else up be compatible. (Lower intake and push rods and everything else) My van is a 1999 Chevy Venture. It had a broke camshaft and messed the cam bearing bores up. Please reply soon with some advice!

[1QUICKHATCH]

Yes the 3400 top end will work fine. After 2000 on 3100's it's the same top end except the throttle body. Did you check your clearances with plastigage? And did you use any lube on the bearings/ journals?

[evartsboy73]

So the heads from the 3400 will be fine on the 3100 block? Sorry But I misunderstood. Just need 3100 head gaskets, Right? Yes I did plastigage the crank and was near the fat one .003 The plastigage bothered me when I checked it because all others I have ever did has never been close to the last reading on the plastigage paper. Think I should use the 3100 crank and see if there is any difference in the plastigage? I have the 3400 crank in the block right now. Thank you for the reply and advice. It is much appreciated.

[SappySE107]

Crank is the same. If the crank is tight to turn, something is wrong. By itself with lube, the crank should spin very easily. Get a 2000+ 3100 head gasket kit. Your 3400 heads will match up with the newer 3100 intake gasket, and give you the right head gasket bore size.

[evartsboy73]

Thanks Sappy I was hoping you would chime in also. All I did was install main bearings and yes I did use assembly lube and torqued them to 37 pounds. It does not spin easily. Matter of fact I have to use slight force with my hand to spin it. And I had not done the extra 77 degree turn on them yet. I have another question. The oil hole main bearing for the rear main cap has 2 oil holes, Right? Well mine does anyways, and only one hole matches up with the oil hole in the cap and it only lines up with half of the hole. This just did not look right to me. I hate when I forget to pay attention when taking something apart. I guess I just assume everything is exact and would go back together smoothly. That is what I get for assuming. Please reply soon.

[evartsboy73]

So you are saying my 3400 intake gaskets will not work also? I can get a whole engine with a bad rod bearing from a 2001 Alero for $50. Is that what I should do? Please reply soon.

[evartsboy73]

Here is a pic of one of the main bearings that I was referring to that just dont look right. Yeah I know the bearing looks bad. It is the number 4 one where the oil pump mounts. Also when I torque all the main caps bolts and get to the last 2 on the number 1 cap it is when it tightens up the crank and I can not turn it by hand. I loosen them a turn and then I can turn it by hand. I torque them to 37 pounds and did not do the 77 degree turn because I knew it was not right. Should it be turnable by hand after torquing the bolts? Please reply soon with advice.

[evartsboy73]

Figured it out. Had a main bearing in the wrong place.

[evartsboy73]

Hi can you please verify that my 3400 heads will work on the 3100 block. I really did not understand what you meant when you said get a 2000+ intake gasket set, Did you mean 2000+ head gasket set? Please reply soon.

[walterdude]

Yes they will work,,, in fact it is a pretty good upgrade.... Before 2000 3100s and 3400s used different heads and intakes... After 2000 they used the same heads and intakes for both engines...Only difference is Throttle Body size.. As far as the gaskets go, I believe Ben was referring to matching the bore size (of the block) to that of the heads... 3100 block/3100 gaskets.. Always wanted to do that to my 99 Lumina... Never needed to mess with the top end,,, not even for LIM Gaskets... And the car had close to 300,000 miles when the frame rotted out of the car....
Hopefully you made some sense out of all that!!
Good luck!!
Tom B....
PS... Somewhere on the WOT Tech site there was a how to that gave a lot of info about the swap....
PPSS Here's a link to some articles that discuss the history of the heads and intakes and info on the upgrade....

https://wot-tech.com/60v6-articles.html

[evartsboy73]

Thank you so much for the reply. This is great info. Now all I need is 3100 head gaskets and I will be ready to go.

[evartsboy73]

Ok I have started putting the engine back together after getting the main bearings figured out. Somehow the rod caps got mixed up. Long story. Yes I should have marked them but I didnt. I have tried and tried to match them up. I even tried with the old bearings because honestly they looked fine. Just wanted to install new ones because I had them. It binds up or something. I put the first two in from the front of the engine and I can turn the crank fine but when I put the third one in and torque it I can not even turn it with a wrench on the crankshaft bolt. Can someone please tell me someway to solve this. Can I order undersize bearings and be ok? The old bearings were well within tolerance. When I torque the first 2 caps they torque fine. Next one seems like it does not want to torque. Totally have hit a wall here. Please reply soon.