The Stovebolt Site Forums The Shop Area Engine Shop Leaking intake manifold rebuilt 261

I have read the previous postings on the subject but still have some questions.

First let me share some basic data.

This is a totally rebuilt 261 stock condition.

Engine circa 1959. First fired up a few weeks ago. Detected some high frequency shrills/whistling..... engine is sitting in frame with no sheet metal......access to components is still good at this point.

I sprayed starting fluid very close to the intake manifold.... both the center and front location created a noticeable increase in RPM. Will verify again with a propane torch and small rubber hose this weekend....(less chance of blowing up the barn).

Here are the questions.

Now that the engine has been up to 180 degrees for a few minutes can I just retorque the bolts or do I need to loosen and retighten...?

I intend to work from the center out during the tightening sequence. I have heard some conflicting torques values....ranging from a low 20 foot pounds to 45 pounds. What are the correct torque values...?

I also read about 3 consecutive tightening sequence after 3 consecutive warm up...... how tight will they be by the 3rd try...?

When I first installed my manifold on the newly rebuilt engine I chased all the thread holes in the head and.... used brand new grade 8 bolts... NOT STUDS..... I made sure the bolts woudl not bottom out and cut and grinded to fit....
Was that a NONO...??? would the proper studs insure a better fit...?

Also.... tending to overdo things..... I removed the locating studs which are found at the extreme end of the head and replaced with good old grade 8 bolts again. Some have indicated that this will this cause the exhaust manifold to stress and leak when it cycles cold to hot to cold to hot.....as it will lack room to expend properly.....Did I do another NONO???

When the mainfolds were first installed, I left the heat connection between the intake and exhaust loose.....tighten everything from center bolts outwards..... the four bolts of the heat chamber were snugged up tight after the intake and exhaust manifold were tightened.

When both manifold were set against a straight edge prior to installation they appeared very straight, not pitted on the contact surface and did not show evidence of being overmilled or ever milled/ground.

Seriously considering buying the previously recommended thick gasket "leak fixing kit"....
as anobody used it with success..... sounds like a good investment.....

Are there any special spells or "incantations" that must be said and washed down with beer when installing the manifolds....??? I will even consider witchcraft....

Thanks for your help guys.....!

Bob Carriere

Are you using the alignment rings between the intake and the head? if not, you'll never stop the vacuum leaks.
Jerry

Yep ...forgot to say that the 3 rings were installed......

Bob

Bob,

You have done everything perfectly. If the intake manifold were to grow with temperature, the head would grow too, so it's a wash.

I haven't used the thick gasket, but it might be the ticket. I have always had the combo machined flat and stuck it on with no problem. Starting fluid is pretty high powered...could your increase in RPM have been a result of some of the concoction finding its way into the carburetor versus a true leak?

If the assembly is truly flat it will seal. If it is warped a tad, the fat gasket, plus all the rest of your great work should pull it flat. Good luck.

Stuart

Procedure is good maybe gaskets are bad. I would try another gasket set with more beer. If it still leaks it's trying to tell you to buy it a dual intake/exhaust. Good luck.

Curt B.

It (literally) sounds like you are real close. Try the thick gasket set (what is this - where do you get it?). The original gaskets were thicker than the Fel-Pro gaskets that I have seen (I have an old NORS set of gaskets that are much thicker than modern gaskets).

I have also used a double thickness of manifold gaskets with good results (with and without using copper-colored, hi-temp, RTV sealant). Some might say that this is an admission or error or defeat - I say if it works, go with it.

The other "final solution" would be to have the pair of manifolds planed/ground to be flat (I do not know what this process is properly called).

I used the thick gasket and it worked like a charm! I can't remember where I purchased it but I'll look after dinner and find out.

Here is the link:

http://www.merchantamerica.com/chevyhotrod6/index.php?ba=product_enlarge&product=57030

OK let me recap.....

Bolts instead of studs is not an issue....

More beer...

Thick gasket kit is probably a good thing.... have one NOS circa 1956 gasket set coming form EBay but will order the one from the link...

Thightening sequence of center out is good....

Will remove outright and check flatness again... mill if necessary....

OUTSTANDING questions...... what is the proper torque values....?

.... what torque value do I follow when re torquing after a good hot cycle...?

.... how many times do I retorque...? some say 3 retorque sequences.....

Appreciate your help guys..... it can get awful lonely out there in the barn......

Ah yes.. one more beer.

Bob C.

RAC1812,

I wouldn't have given much thought to torquing those bolts had you not asked the question. I looked in a manual, granted it was for a 235, but interestingly enough, it showed a torque of 25/30 ft/lbs for the two bolts nearest to the heat chamber and 15/20 ft/lbs for the remaining bolts.

I don't think this is a critical issue at all. If you tighten from the center outward, and don't over tighten and stretch the fasteners, you are going to be fine.

A flat manifold bolted to a flat head with a good gasket is far from rocket science.

The pregnant question is...what kind of beer are we talking here!

Stuart

Rickard's Red or Alexander Keith Ale.....good stuff.

As a follow up..... new thick gaskets have been ordered......

Meanwhile I went back over the bolts. A bit of a problem ... in fact impossible to use a torque wrench in the center bolts.... so we approximated. After warming up th engine we gave it about an extra full 1/4 turn.... then using the dial troque wrench set at 30 / 32 gave a similar 1/4 turn tot he bolts and got a "click"

Had a beer.....kidding!!!

Fired up the engine and the whistling had gone... we then went over all the suspected vacuum lines and doped up the PCV fittings just in case and tweaked the dizzy advance lines.

Idling is marginally better...... still need to use the choke fully and fast idle. Imay have overcarburated the engine with a NOS surplus military Rochester and getting tooo much air at too slow a speed to suck the gas out of the venturi....

If CarbKing is on the side..... I am using a Rochester 7015011.... but may go back to the original 261 "B" I rebuilt using a kit from CarbKing......

Thanks for all your help.....

...parts ordered will not be wasted as we have another 235 and a Pontiac 261 in the works as well....... beside we hear that manifold gaskets have been known to burn out when these engines are driven at high revs for sustained periods.
Our trucks are geared down right hand drive WWII Canadian military models with a top speed of 45 mph going down hill..... axle ratio is 6.39... on 16 inch tires...

Wish it was easier to post a picture on the forum.

Bob C.

Talked to soon..... still have a leak on the intake ...front intake port for 1&2.... and an exhaust leak at the rear port on 3&4

Amazing what you discover once the muffler is installed.... also removed fan belt for a short run...... without the blast from the fan you can test for leaks a lot more accurate.

Even disconnected the PCV to see if the idling would improve... not such luck.

Will now wait to get the special one piece thick manifold gasket set before doing anymore harm.

Frustrated....Bob

Update...... picked up my new gaskets at the UPS store. Quite surprised at the 1/8= thickness fo the gasket.

Question for Virginiafiretruck and others who may have used the thick gasket......

The gasket looks like some heavy duty stiff carboard......any idea of what it is composed of.... How long will it last under the heat and fire of the exhaust pipe...... When one considers the torching/cutting damage that can be done to the head and manifold when driving too long with an exhaust leak??

To be safe I also got a new set of 3 rings for the intake ports.

Any comments...?

Bob C.