Stroking it!

[Kman]

My son just bought a 4.2 crank for his YJ at Advance Auto.$173.00-his old crank was worth $20.00 as a core.It's been turned .020 on both rod and main journals.

[rick]

Looks fast anyways... I think that is the last 4.2L crank core in the US. Napa didn't have one when I first tried to order it (right after you did Chuck), and I have been through 3 places that say "yeah, sure we have one of those..." only to find out after they actually look on the shelf that they are out of them. I have started expanding my search...my father is looking for one in the engine scrap yards of good ole Detroit...

[NAILER341]

it sure is perty

[cbremer]

even if it doesn't run, at least it looks good







going to indiana over this weekend, so I hope to work on swapping it in next weekend. maybe it'll even start

[Kman]

Sounds Good!My son and I are going to rebuild the '82 258 in his '89 YJ(he now wants to paint it AMC blue..LOL).It's going to be a basic rebuild with a 4.0 head on it.
Keep this thread going we want to see your finished product!

[cbremer]

thanks! you learn something new every day

as a small update- i've got the bottom end done (just have to make a little clearance for the oil pump and bolt on the oil pan) and i'm almost done with the long, painful process of porting the head and intake. not so much to enlarge, but more along the lines of port matching, at least on the intake. the exhaust is getting opened up a bit to take advantage of the header

with any luck... another 4 to 6 weeks just because i'm a lazy bastid

[Kman]

I just read this thread and wanted to comment on the machining issue.When a block is align bored the main caps are removed and the bottoms cut on a cap grinder.They are reinstalled on the block and it is then machined to factory OEm specs.This actually moves the crank up in the block slightly but that is how it is done.
Like wise when a rod is rebuilt the bolts are removed,the cap and rod shaved and bolted back together(preferably with new bolts).The hole is now smaller and obviously out of round.It is then honed to the correct diameter and checked for size and roundness.This process actually slightly shortens each rod.
Just adding my 2 cents...

[Elusive]

thats actually the 4th one I have seen, and every time it was the number 6.

[rick]

Duh, sorry... I guess I was in a hurry when I replied. Hmmmm, stock and broken rod? That beats the heck outta me. I have never heard of broken rods in either the 4.0 or 258. There's a first for everything...

[Elusive]

I broke the rod when the engine was stock. I have not had any problems since I built the stroker.
CR is about 9.6/1 or so... not really that bad.

as to detonation problems... um.. I talked about that in the previuos post...

[rick]

If you didn't dish the pistons and you used 258 rods, isn't the compression ratio approaching 9.7:1? Maybe this higher compression is part of the rod failure? I guess that kind of increase should not cause a rod to fail, but maybe related? Did you have detonation problems?

[Elusive]

I just noticed this thread...
I built my own stroker 2.5 years ago.
I used the 258 crank and rods, but I had the 258 crank offset ground a bit to help with the quench. I have done a lot of research on this and it is now generally accepted that the quench isnt nearly as important as the compression ratio when trying to control spark knock.
That said.. I have always run premium in the stroker, but I noticed that when I was on the east coast I could buy 93 octane premium and it was a lot better mix than the 91 octan california crap. I started to get a little spark knock out here, so I built an adjustable MAP sensor and it eliminated it....though at the cost of some MPG.

My stroker is a 97 OBDII stroker though... 24# injectors from the factory.. I'm sure this helps.. I also have the desireable coated pistons from the factory. I had to cut the tab off the distributer and index the distributer a bit for the computer to pick up the signal. I also had to space out the bottom skirt plate thingy with some washers so the bottom of the rods didn't hit.... But my stroker only had 19000 miles on the block when I broke a rod.. I didnt even bore it, and the ONLY changes I made were the crank and rods.( OE pistons)Oh, I have a very low RPM cam in it too.. probably too mild actually, but I have incredible throtle responce.

If I was going to build another stroker ( I am going to) I'm gunna deck the block and dish some silvolite pistons with the 258 crank and rods again. I think the 24" injectors are enough for a rock crawling stroker with a mild cam.. If I were turning serious RPM I'd get bigger, but I think that the piston speed in a stroker is too high to expect the engine to last at redline all the time.
The only thing I really dont like is using the stock rods. I have broken 2 connecting rods. If I were gunna spend $$$ on aftermarket internals I'd buy rods first.

my stroker runs very very strong.. I really notice it when I get into my wifes 2000 tj and drive her 4.0.. I have so much more power than she does. Before the MAP sensor, I got about the same milage as before I stroked it. My stroker has 11000 miles on it, and many many of those miles are wheeling and/or idling at 2800 rpm running the OBA or welder.

[rick]

Yes, he has a good site for stroker info. I think the MAP adjuster setup he made is a little crude, so I am thinking of maybe putting it in a nicer box or something from Radio Shack to keep it a little safer. I'll post pics when I get to that point.

[NAILER341]

Originally posted by rick
Thanks man. I saw those on ebay... the problem with his auctions is they are for V8s so you pay for 8 instead of 6... I found the Jeep injectors on their site here. I'm still not sure if 24 lb/hr is enough...

just call, or email him, and he will sell you what you need.

[cbremer]

i found a good deal on ebay for a set of 26 lb/hr accel injectors, so i went with those. i felt that 24lb would probably run a little lean (or running too long a duty cycle), 30lb a bit rich. without looking, i bet erik's link is to 5-0 motorsport i bought my stock 19 lb/hr replacement injectors from him (originals were leaky) and had them the next day- they're still running perfectly!

i've also seen (on ebay) some newer Delphi (GM?) fuel injectors that will supposedly fit bosch-type FI systems. don't know about those for sure- didn't want to be the one to find out that they don't work

Dino has good tips & tricks about how to fine-tune your flow rate by making an adjustable MAP sensor here: http://www.angelfire.com/my/fan/MAP_adjuster.html

his main site: http://www.jeep4.0performance.4mg.com/index.html