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Old 02-29-2012, 01:12 PM
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Compression Values For Engine That Refuses To Run

Over a period of time after running so well my SBC started to
idle bad and shake like it was out of balance. There was a chuffing noise coming from the motor heard better with car trying to idle and hood down.
I decided dismantle the motor after trying a different carb, coil, fuel pump,
adjusting the valves and installing my new MSD6A Digital box.
Upon removing the intake manifold I found this had happened on the front cylinders.


Assuming I had got the culprit I ordered up my intake gaskets and a few days later reassembled the motor.
Today I "started" it, itīll only run if I peddle the gas and keep the revs up,
if I do not it just dies, the chuffing noise was not evident.
A compression check showed;
1. 170........2. 175
3. 175........4. 175
5. 180........6. 175
7. 170........8. 175

Pretty disappointing numbers, my Brodix head is 64cc and the valves are 0.020 down the bore and I used a thin 0.015 head gasket, my comp calculator says 10:95.
Iīm going to readjust the valves again, but could I be looking at head gasket replacement ?

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Old 02-29-2012, 01:23 PM
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Quote:
Originally Posted by malc
A compression check showed;
1. 170........2. 175
3. 175........4. 175
5. 180........6. 175
7. 170........8. 175

Pretty disappointing numbers, my Brodix head is 64cc and the valves are 0.020 down the bore and I used a thin 0.015 head gasket, my comp calculator says 10:95.
Iīm going to readjust the valves again, but could I be looking at head gasket replacement ?
What's disappointing about the numbers? Higher numbers could detonate on pump gas, depending on the remainder of the build. The chuffing was probably a header/manifold leak and you fixed it. It won't remain running because you have a vacuum leak, either external or internal at the manifold/head interface. Check the manifold for level and smooth. Check the heads for level and smooth. Check the angle of each one where they meet. I'm bettin' the heads and manifold are not parallel in either X or Y planes, or maybe both.
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Old 02-29-2012, 01:57 PM
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Is there a reason you installed to gaskets dry? RTV is your friend! I wouldn't goop it on there but I use it on every intake gasket and have NEVER had one leak, I've even used it in place of an intake gasket without leak. The other issue is make sure your gaskets are NOT covering the port as they are in the picture. you can trim them with a razor blade or a dremel. you want them to be as close to the exact port dimension as you can get.
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Old 02-29-2012, 02:38 PM
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I installed Fel Pro Q1206, sized to my Brodix heads.
It appears I didīnt use or failed to use enough GasGacinch on there,
but this time I did it right, glued them first to the heads and later the intake to the gaskets.I then let that and the RTV on the water ports setup up over three days.

The heads are just three years old and like new still on the intake surface,
the AirGap manifold is somewhat older, still cleans up nicely.

I see there is another gasket I could use Fel Pro Q1266 which is 120 in. thick,
the other is .060 in. thick, thatīd take up any discrepancies, if any, ītween heads and intake.
Maybe I should choose a gasket sized to my inlet manifold and not the heads,
the inlet manifold has smaller ports.

Edit: Iīve just been to Summit and the FelProQ1266 gaskets are the ones
recommended for the Edelbrock AirGap.



(Before this "final" rebuild of head/intake I did a real goof up, over my lifters is an oil splash shield, which I removed to check my lifters.
After getting the intake on and most ancilliaries I went to install the distributor, wouldīnt go in.......I had replaced the splash shield back to front,
a 1/4" of metal said the distr. wasīnt going back in.....
I also found out two days is not enough for the glue and RTV to set when the nights are cold and days chilly.)

Last edited by malc; 02-29-2012 at 02:48 PM.
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Old 03-02-2012, 05:12 PM
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I agree with Techinspector1 I've seen some of his posts and he gives good advise.
You might check your brake booster and anything else that your vacuum lines run to.
You might also figure out why those gaskets crept like they did.
Also think those compression numbers are fine, if your not blowing compression into your radiator no need to replace them.
One reason those gaskets could creep is the surfaces are not flat, a straight edge and a feeler gauge will make quick work of that.
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Old 03-02-2012, 05:21 PM
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Sometimes gaskets creeping like that is because of inproper torque on the intake gasket. If you start at one end and work to the other it can move the gasket. If you start in the middle and work out each direction it will seat better.
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Old 03-02-2012, 07:00 PM
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Gasket creep like that can also be caused by no dowels installed in the block for the heads , the heads shift and the trouble begins.
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Old 03-02-2012, 08:06 PM
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Quote:
Originally Posted by ap72
Is there a reason you installed to gaskets dry? RTV is your friend! I wouldn't goop it on there but I use it on every intake gasket and have NEVER had one leak, I've even used it in place of an intake gasket without leak. The other issue is make sure your gaskets are NOT covering the port as they are in the picture. you can trim them with a razor blade or a dremel. you want them to be as close to the exact port dimension as you can get.

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Old 03-02-2012, 11:35 PM
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I use GasGacinch on my intake gaskets around the ports, RTV on the water ports, just a smear.
Once the intake gaskets are on the heads I let them sit for awhile so as not to move them when I lay the intake on.
After laying the intake on I tightened the bolts to finger tight and let it set,
then I tightened them down starting in the middle criss crossing out to the ends.
The block has dowels.

As I stated before it seems I didīnt use any or enough glue around those ports.

I started the car yesterday and itīs still showing the same sypmtoms.
The leak or whatever is so big the car just cannot idle, I only have a brake booster, vacuum gauge and distributor sourcing vacuum from the motor.

Thicker intake gaskets are on their way, Iīll do it again.

In the meantime what can I do to check the brake booster,
Plugging the line to it maybe ?

Thanks for thinking about this.
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Old 03-02-2012, 11:52 PM
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This type of "gasket creep" is almost directly related to not retorquing your intake after a few warmup cycles, I've seen it many times...there is no such thing as non-retorquing gaskets unless they are cork when mixing AL and CI components.

The differing expansion rates are the cause.

I agree you have a vacuum leak somewhere, you can spray ether starting fluid around the intake to assist in finding it.
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Old 03-03-2012, 02:52 AM
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Quote:
Originally Posted by 4 Jaw Chuck
This type of "gasket creep" is almost directly related to not retorquing your intake after a few warmup cycles, I've seen it many times...there is no such thing as non-retorquing gaskets unless they are cork when mixing AL and CI components.

The differing expansion rates are the cause.
I agree you have a vacuum leak somewhere, you can spray ether starting fluid around the intake to assist in finding it.
I do tweak the intake fasteners occasionally, not wanting to over torque the aluminum parts threads, I keep it all tight.

Heads and intake are both aluminum.
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Old 03-09-2012, 02:17 PM
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Finally got this SOB back together today.
Cranked the motor.
Something goes Bang......motor locks up.
The starter pinion had ridden up onto the flexplate ring gear,
two pinion teeth sitting on two ring gear teeth.
I had to unbolt the starter to release the mating pair.

I took out the sparkplugs and turned the motor by hand,
nothing internal seems to be damaged.

Could this be a one off bad experience or does that starter have to be looked at ?

Itīs one of Summitīs small high torque starters, been on the car a looong time.
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Old 03-09-2012, 02:55 PM
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Sounds like a one-off thing to me, perhaps the rough idle moved the starter some? Was it cocked when it jammed?

When chasing a possible vacuum leak, be sure to look all around vacuum hoses for cracks, then can be hard to see and won't always leak until moved around. Unplug any lines you can at the source and block the openings with a finger one at a time.
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Old 03-09-2012, 03:08 PM
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Quote:
Originally Posted by 68NovaSS
Sounds like a one-off thing to me, perhaps the rough idle moved the starter some? Was it cocked when it jammed?

When chasing a possible vacuum leak, be sure to look all around vacuum hoses for cracks, then can be hard to see and won't always leak until moved around. Unplug any lines you can at the source and block the openings with a finger one at a time.
"Cocked", do you mean starter on block ?
The starter was in itīs place, the flexplate must have "flexed" a little.
Iīll check the starter shimming next time I go under there.

Doesīnt even get so far as to idle.....

The only vacuum connections I have are brake booster, PCV and distr. vac advance.
All hoses are new.
The manifold has just been reinstalled with the thicker gaskets,
when I took it off it came off clean hardly any resistance, just the RTV
seemed to hold it down.
The gaskets stayed on the heads but hadīnt stuck to the intake,
Iīve got a feeling GasGacinch isīnt so efficient.
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Old 03-09-2012, 03:39 PM
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how about your base gasket.. (carb to intake)
if intake has egr and plate is that gasket good, my edle intake has the port for an egr and it's blocked off with a plate, and it was sucking air..

also are you running an HEI or a seperate coil.. if you hook the coil up backwards it not idle with a msd box. it'll run but like crapola
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