AARGH! The 1G 7-bolt Frankenblock: Crankshaft. 1Gb rods

[ricky750]

I've got a '94, AKA the 1G 7-bolt. I've spent a good amount of time looking, everyone's talking 1G or 2G, 6-bolt or 7-bolt... but there doesn't seem to be a lot of GOOD information about the 1Gb 7b block. Hopefully some of you gurus can shed more light on a couple questions I have.

So, once and for all...

Specifically, I wanted to know more about the crankshaft and block. Stop me if i'm wrong, but the 1G7 block is basically a 6-bolt, complete with oil squirters, that happens to have a 7-bolt crank, 2G rods, and 2G pistons in it? So, in this case do I need to do any sort of prep to my engine (besides 6-bolt rods) to be able to fit a 6-bolt crank, or will it swap in with minimal hassle?


That was the main question, but this second one gets a little more interesting:

RODS:
6-bolt rods are thinner than 7-bolt. So the 1Gb with a 7-bolt crank had to have 7bolt rods to fit. BUT If all 1G's are 7.8:1, how does the 1G7 block achieve that compression with 7-bolt crank, rods and 2G pistons???

Logic tells me Either:
1)The 1G 7-bolt rods are shorter than 2G 7-bolt rods.
2)The 1G 7-bolt rods are connected to 1G 6-bolt pistons? (but 93-99 is same piston part #)
3)1Gb ratio isn't really 7.8:1, but 8.5:1
4)The universe is about to explode.

I know some of you guys out there have wondered this, I know someone out there has a mess of knowlege just waiting to share with us:

This would be a big help to us guys with the 1gb frankenstein car pieced together out of 1G and 2G components, and save a lot of unnecessary profanities from coming out our mouths whenever we buy/find/fab parts just to discover the whole damn setup won't work.
thanks in advance,
-R



(mods: please move this post where you think it has the best chance of getting answered accurately, and be the most help to others on this forum)

 

[ricky750]

Hey guys, I know it's uncouth to bump a thread, but does no one know the answers to these 2 questions? So much time... no replies. Come on, somebody step up, I'm trying to rebuild/revamp my short block here, and really could use the advice.

thanks a lot,
-R

(For those who didn't want to read post #1, my questions were, simply stated
1) Can a 1G 7-bolt block take a 6-bolt crank setup with minmal hassle? (6bolt rods)
2) How is it that the 1Gb Rod/Piston setup can achieve 1G compression ratio (7.8:1) using 7-bolt (8.5:1) components?

 

[dherron]

For an 7bolt block i am sure that the main journals are a different diameter. Something like 5mm or so. So for a 6 bolt crank to fit in the block you would have to have the block machined to fit the bigger journals. Or just make this all easier on yourself and buy a 6bolt block and crank which i have for sale in the classifieds. Would make things much cheaper and faster.

 

[dherron]

Also the rod length is the same on every 4g63 from the early galant vr4 to the new evo's.

 

[gsxtacy]

Search Function is your friend.

This is one of the more common 6/7 bolt questions.

Repeat after me: I will either build an ALL 6 bolt component 4g63T OR I will build an ALL 7bolt 4g63T.

1G's ALL have 7.5:1 CR PISTONS.

2G's ALL have 8.5:1 CR PISTONS.

See the difference? PISTONS.

Save yourself ALOT of hassle/worry/trouble and BUILD A 6 BOLT.

Drop it in, and forget about it.

BTW, don't BUMP your own posts, I nearly reported this to a Moderator for CLOSURE.

Search more for any answers you need. And stop trying to mix/match parts that were NEVER designed to be mixed/matched.

Its also pretty obvious that you can talk about mechanical stuff but you don't have alot of experience in Vehicle Repair.

IMO you should let a reputable shop handle your repair.

Good luck

 

[timloomis]

the 1g 7 bolts arent as crappy as the 2g ones.and a neat little secret too,it wont crankwalk and the wrist pins are the same as 2g pistons.so you can just pop in some 2g pistons and you wont have to get the rods machined.

 

[Spoolin4Ever]

"the 1g 7 bolts arent as crappy as the 2g ones.and a neat little secret too,it wont crankwalk and the wrist pins are the same as 2g pistons.so you can just pop in some 2g pistons and you wont have to get the rods machined."

Well it's still weaker crank and rods then the 6 bolt.

And the 1G 7 bolts do crankwalk sometimes.

6bolt or nothin

 

[huafist]

the 1g 7 bolts arent as crappy as the 2g ones.and a neat little secret too,it wont crankwalk and the wrist pins are the same as 2g pistons.so you can just pop in some 2g pistons and you wont have to get the rods machined.

I can go today and take pictures of a 7-bolt from a '94 that crankwalked. you can grab flywheel, lift up, and the crank moves nearly 0.5" before the block lifts up.

That aside, I've said time and time again crankwalk is overstated. Just because you have a 7-bolt doesn't mean it'll walk, and just because you have a 6-bolt doesn't mean it won't walk. If you've got an engine that's in good shape (good compression, no excessive bearing wear), there's no reason to swap it for a 6-bolt.

 

[Spoolin4Ever]

True....but he was talking about putting some time and money into it. If you are in that position, the money is better spent on a 6 bolt. That's all I was trying to say.

Then next thing it turns into some 7bolt 6bolt debate blah blah.

He could have searched and found this all out within an hour anyway

Some people build 7 bolts with good luck, but best to err on the side of caution. It'd suck to build it and then have to replace soon afterwards.

 

[RiceKiller_TSi]

Repeat after me: I will either build an ALL 6 bolt component 4g63T OR I will build an ALL 7bolt 4g63T.

I agree with this statement. One or the other for simplicity.

I have a 1gb 7bolt but found it beneficial to use the higher compression 2g pistons with the existing rods and then slap on the mls headgasket to lower the compression a bit.