MyFirst90coupe

I changed the intake manifold gasket on my 90 L98 this week. When I went to put the intake manifold bolts back in I noticed that there were 2 different lengths of bolts. Of course I didn't notice this when I took them out so I had no idea where the longer ones went. I guessed and put one longer one and one shorter one in each location then torqued them in the pattern that the FSM said to.

Now when I fired it up it seems like something is binding up. It idles along and there will be like a pop/bang noise.

Is it possible that the longer bolts are in the wrong location and interfering with the pushrods?

Thanks,
Jeff

rlf105

I did my 90 intake over the summer. If memory serves me right the longer bolts go on the outer corners of the manifold and are also torqued a little more to seal the front and rear of the manifold.
I dont think they were long enough to hit any pushrods or anything though. did you check you timing? just a thought

JackDidley

Its been a long time, but I think its very possible, the bolts are hitting the pushrods.

engle1147

I really don't think this is possible.

Why did you change the gasket in the first place?
Your sure you got the distributor has been fully dropped back in on the "correct" tooth?
Oil pressure is good?
Wires on the dizzy are correct?
Checked the base timing?

ch@0s

It is possible. I had that issue when installing mine the fist time. the shorter bolts go in the middle if I remember correctly.

EastCoastHD

Not sure of the correct location of the longer bolts, possibly the outside corners, just a guess. I had my intake off last year and can't remember for the life of me.

This is how I organized my bolts...


This is a close-up off cyl. #4. The exhaust pushrod sure is close to that bolt hole. 1 & 5 exhaust look tight also.


If it were me, I'd tear it down and install the bolts correctly. GM used long and shorts for a reason.


Incorrect per my 90 FSM. All intake bolts torqued to 35 lb.ft., except position 1&4 (passenger side center)45 lb.ft.

engle1147

Holy crap-a-mundo I guess it is possible given a long enough bolt. Looks like I dropped the ball on this one. Nice photo shot EastCost

MyFirst90coupe

WOW! That is an awesome picture! Scary. I would have double checked before I put them in but I already had the manifold down on the sealant.

GREGGPENN

Interesting. The intake-to-head bolts on my 89 were all the same length (1 1/8"). There was a thread that pointed out if 1 1/4" bolts were used, contact with the push rods holes would occur. And, that contact would be on the center two holes on each side.

If you had shorter bolts, it seems like they should have gone in the middle.

MyFirst90coupe

I'm thinking I might just pick up 12 3/-16x1-1/8" SS allen head screws and swap them out one by one so I don't mess up my seal.

Any opinions on if I might have messed anything internal up?

SunCr

When GM redesigned the heads to accept intake gasket retainers, they made the outer water jacket bolts longer. Didn't think any of those heads or gaskets made it onto anything other than the '91. If you take it back off, see if the outer bolt holes on the heads are counterbored for retainers. If so, that's where the longer bolts go and you should use the gaskets with the retainers as they maintain perfect intake gasket alignment which stops most of the leaks.

samsonb

There are some guys who replace the stock GM intake bolts with some ARP bolts. As alot don't like torx type bolts GM liked to use.

One thing you could do is get a C4 parts catalog and see what intake bolts call for a different part number.

Pete K

I have never seen different length factory torx bolts that secure the base to the heads. I wonder if this was the case on all c4's or just certain years.

samsonb

According to my parts catalog. The intake bolt part number is 14091547. And is 3/8-16 X 1 1/8.

I say you'll have to chase the threads and put new sealant on the bolts. I'd look to see what ARP bolts others are using for their intake bolts.

WW7

When I put the intake on my 383 about 4 months ago I ordered new intake bolts from GM and they were all the same size from the factory.I also have a set of Summits intake bolts with hex heads and they measure 1" instead of the GM length which are 1"1/8..You may be able to replace them one at a time like you were saying. I would start in the middle and work my way out just like the tightening sequence,just remember to redo the sealent on the threads..You really have nothing to lose, if it leaks then you can replace it. ..WW

ch@0s

I guess my post was to small and over looked. My 91 had different size bolts form the factory. I had the same problem the short bolts go in the middle. Maybe you are right and it was only certain years.

Pete K

Having a bad day?

Pete K

Hopefully this gets noticed.

Pete K

Now we got it covered.

JackDidley