258 vac leak at intake manifold

[qmichael]

I have a 85gwag w258 stock carb . Just R/R carb last summer ,can't reblace carb w/ a better one just yet due to emissions testing once a year.What I have found is that I have a big leak (vac) near # 6 on the intake I found this by using carb spray (W/a straw)and found that the rpm went up! What I need is what is the tighting bolt pattern on this and if I should new bolts when I put it back together (what size so I have them on hand if I break one god I hope not). I plan on R/R intake & exaust gaskets this weekend. Are the bolts all the same size/ length , what is the thread, foot pounds, tips ?

[tgreese]

Tips? it's a pain on an FSJ. The last bolt on the firewall end is v. hard to get a torque wrench on. I ended up using my calibrated forearm on a long-handled rachet. I also used a 2x3 piece of plywood to cover the pass side of the engine compartment so I could scoot out over the plywood and reach the bolts.

I'll post the pattern later this afternoon, although it'll be from a '77 manual.

BTW the manifolds will come off in two pieces if you disconnect the EGR exhaust tube between them. It can be tough to put it back after the manifolds are torqued up though (ask me how I know ;) ).

I replaced all the bolts, nuts, studs and lockwashers and used anti-sieze paste for reassembly. You must reuse the big hardened washers, but the bolts and studs are ordinary grade-5 steel from the hardware store.

Leaky manifolds is pretty common on the AMC I6, so do a careful job, don't cut any corners, and retorque the bolts after a few days, and then again after a week or so.

[LRRH]

are you sure it's the intake and not the valve cover?? either way it's not that big of a deal. if it's the intake follow the steps given above. if it's the valve cover upgrade to a metal one if you've still got the original plastic POS.

[qmichael]

Defintely on the intake, I was going to R/R gasket on the valve cover anyway when I was in there. If it was the valve cover leaking would not the rpms drop off every time you put oil in ,if it was running? Still need info in the frist post. I was going to use grade 8 stainless steel vice grade 5. help!

[tgreese]

Mmm, no need for grade 8. Won't hurt, but it's just an extra expense. Also, there's a stud in each end that you likely won't be able to find easily in grade 8. The anti-seize goop is the real deal though. Breaking off bolts on the I6s isn't a big problem like it is on the V8s, for some reason. At least, in my experience.

I think LRRH's point with the valve cover was that, if there's a leak, the starter spray will get sucked in at the carb base with the PCV airflow and speed up the motor. Sounds plausible to me. Anyway, those plastic valve covers leak even if you replace the gasket and do everything perfectly. There's some kind of special foam gasket from Victor that's supposed to work, but the usual fix is an aftermarket metal valve cover.

Still at work - no torque pattern yet.

[ January 22, 2004, 02:42 PM: Message edited by: tgreese ]

[tgreese]

Ok, here's the drawing from my '77 manual.
http://www.nmr.mgh.harvard.edu/~reese/torquepattern.jpg

All bolts are 3/8-16 size. The two end locations (2 & 3) are studs, useful for guiding the manifolds into place. The '77 has the all-cast-iron design - your manifolds don't have bolts 12, 13, 15 and 16. 1 and 14 are shorter bolts, all the rest are the same length and bridge the two manifolds with the large hardened washers.

hth :cool: Tim

[tgreese]

The foam gasket isn't from Victor, it's from Felpro, and the material is called "Sponge-Lam". Felpro P/N VS50244R

Check the price before you order!

[ January 22, 2004, 05:36 PM: Message edited by: tgreese ]

[tgreese]

Oh yeah - torque settings. Intake and exhaust manifold bolts, 23 ft-lbs. Exhaust pipe to manifold, 20 ft-lbs.

[Ralph]

Also a good idea to use a thin coat of Permatex Ultra Copper on both sides of the intake manifold gasket. From my experience and reading others', there are issues with slight warpage in both the intake and exhaust manifolds over time, so the extra sealant for the intake manifold will help prevent vacuum leaks.