I did the PCV replacement back in July 4th. When undo all 7 screws of the intake manifold, one of the 4 lower screw had difficulty to come out during the unscrew process. All other 6 screws came out so easy and smooth except this one. I encountered resistance while unscrewing. I worked it out slowly and finally it came out. I could see the screw threads had aluminium on it. Now, the oil separator and all hoses are replaced. I worry about this particular screw may not be able to be tightened. I am going to use all new 7 intake screws to install the manifold. Would this problem screw hole in the engine block cause any leak after installation ? This screw hole is the 3rd hole from thermostat housing. This was my very first PCV job. So I think that the screw hole may already bad before I unscrewed the intake manifold screw.

Also, I was so surprised that the lower hole between oil separator and engine block itself was so clean, no built up after 16 years/250k miles. I saw other members' pictures and most of them were clogged up with gunk. The throttle body hole into EGR valve was plugged up with gunk !!

Any comment on the stripped intake manifold screw hole is appreciated. I have not installed the manifold yet because I am waiting for the Volvo part (metal nipple between EGR valve and EGR tube). I could not reuse the old one because it stuck inside the old EGR valve so bad. I just broke the nipple when trying to unscrew it !! Same thing to the EGR temperature sensor. These 2 parts were there since 1995.

Ching-Ho Cheng
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1995 855 NA, Bilstein Strut & Shocks, Volvo Protective Grill, K&N Filter, E-Code Lens, ClearCorner Light, Alpine CD-Changer, AutoDim RearView Mirror, 6000K HID

If I were in your shoes, I would want to do a test install of that one screw BEFORE mounting the manifold back up.

Having not ever done this job yet on our white blocks, and only picturing the situation, screw sizes, etc., I would offer up the following which is just an opinion and subject to discussion/critique as usual.....

Run the correct size/thread tap down the hole just to clean things up a bit. Then insert the screw with a bunch of flat washers stacked up to the same thickness of the manifold, making sure the first washer in the stack (the one against the engine head) is fairly large area so that you don't leave an imprint in the aluminum due to the washer being too small. A flat piece of metal with a hole drilled in it would be even better, so that you distribute the load better. Then see if you can tighten the screw to the recommended torque without it stripping whatever threads are still remaining in the head. If the the theads are so bad off that they won't support the recommended torque, then you don't have much choice other than to drill and tap the hole out to the next size. Never increase the hole diameter any more than absolutely necessary. Drilling or rat tail filing the manifold hole may also be required. If you end up having to do that, you may want to mark the bolt head and the surrounding area on the manifold with some sort of bright paint to alert the next guy (maybe you a few years from now) that something wierd is up and not to mix up the screws.

Chris,

Thank you for your response. I have never tried to use a drill & tap and don't have any tool to do that :(. Why we have to use tons of flat washer to simulate the manifold thickness ? How do we recreate the thread in the hole using drill and tap ? Do we have to re-create the thread to the next size up ?

Ching-Ho Cheng
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1995 855 NA, Bilstein Strut & Shocks, Volvo Protective Grill, K&N Filter, E-Code Lens, ClearCorner Light, Alpine CD-Changer, AutoDim RearView Mirror, 6000K HID

The best outcome is if you can stick with the same size screw and NOT have to drill it out larger. I'm just saying it's often a good idea to run a tap down into the hole to clean out any loose threads that may be lieing in there and would hinder the smooth installation of the new bolt. In this case the tap would be the same size and thread as the original screw - no drilling required. Running a tap in there isn't an absolute requirement though, as long as the new screw will screw in without a lot effort. Also, any time you do use a tap, you want to be very careful not to snap it off in the hole. That can ruin your day. If it's too hard to turn, stop, wait a minute, and then carefully back it out.

There are a couple reasons you want to simulate the manifold thickness when test fitting the bolt. One is to keep you from accidentally driving the screw too deep into the hole and "bottoming-out" which might do serious damage like punching a crack into the water jacket. Another reason is so that you are engaging close to the same number of threads that will be engaged when the manifold is in place. This will give you more confidence that the threads can support the finish torque without stripping.

One thing you can sometimes do is to measure the depth of the hole with a sturdy piece of wire and see if you can get away with using a SLIGHTLY longer bolt in order to engage some more threads. But you have to be VERY CAREFUL in measuring the hole depth, adding the manifold thickness, and comparing this to the screw length, due to the possibility of bottoming out as mentioned above. If you decide to try this, make sure you can EASILY insert the screw at least a bit further than it will need to go when you are actually tightening the manifold.

At any rate, it's only if you can't get the screw to hold torque, that you would ever have to consider drilling and tapping oversize.

Chris,

One question about rethreading, the intake manifold screw/bolt is M7x1.0. What size of rethreading tap should I use ? I search the Internet and could only find M6x1, M8x1.25, etc from Heli-coil. There is no M7x1 rethreading tap ??

I have not tried to put in a new screw, I will do it this evening.

Thanks,

Ching-Ho Cheng
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1995 855 NA, Bilstein Strut & Shocks, Volvo Protective Grill, K&N Filter, E-Code Lens, ClearCorner Light, Alpine CD-Changer, AutoDim RearView Mirror, 6000K HID

Right now, you are NOT trying to retap the thread, just to clean the threads out.

Therefore, you DO NOT want the helicoil tap, they're different. This set will have the M7, and covers your needs. You're just looking to clean the treads out/remove any spurs not re-tapping the thread.
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If you're not driving it "like its stolen," are you really driving?

You would want to use the same size / thread pitch tap that the hole is already tapped to. If you can't find that particular tap then try inserting the screw as-is.

Chris,

I just tried new screw, my heart sink !!! The screw could not even be screwed in. I tried other 6 holes, it went right into the hole. Thread in the beginning of bolt hole was stripped already.

I have never done any rethreading so no idea how to do it. I also worry about damage to the engine block :( I may have to have the car towed to garage to rethread the hole ....

Ching-Ho Cheng
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1995 855 NA, Bilstein Strut & Shocks, Volvo Protective Grill, K&N Filter, E-Code Lens, ClearCorner Light, Alpine CD-Changer, AutoDim RearView Mirror, 6000K HID

Chris,

Thank you for the detail explanation. I will try the new screw first with flat washers and find out the screw thread size for getting a same size tap. I hope that the situation would be that bad .....

Ching-Ho Cheng
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1995 855 NA, Bilstein Strut & Shocks, Volvo Protective Grill, K&N Filter, E-Code Lens, ClearCorner Light, Alpine CD-Changer, AutoDim RearView Mirror, 6000K HID

The bottom bolts on the intake manifold should not have been removed, just loosened. The bolts can be reused because of the low torque value (14 lbs).

As for the stripped bolt, try putting a new or cleaned off bolt back on, with enough washers to simulate the thickness of the manifold. Then torque it down to 14 lbs. If it holds tight, you should be good to go. Otherwise, you will need some work.

The bottom bolts need to be put in place before you put the manifold back on, those bolts will hold the manifold in position while you 'finger' tighten the top bolts.

Remember, the bracket under the manifold should be loose on the bottom bolt and only tightened after the top bolt is secured to the manifold.
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My name is Klaus and I am a V♂lv♂holic

Klaus,

Thank you for your response. I am going to use 7 new screws on intake manifold. That's why I removed them all. The support bracket is pain in the neck. I will have to remove the fan shroud to get more space to tighten the bracket to the bottom of intake manifold with the bottom bolt loose. I did not do that when I unscrewed the bottom bolt. It took me almost 1 hour with 2 swirl extensions to get to that bolt (weird angle) from the bottom of the car. If my daughter was there to help me, it would be faster. The Oil dipstick bolt was easy from the bottom straight up using extension.

Ching-Ho Cheng

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1995 855 NA, Bilstein Strut & Shocks, Volvo Protective Grill, K&N Filter, E-Code Lens, ClearCorner Light, Alpine CD-Changer, AutoDim RearView Mirror, 6000K HID

I didn't do anything from the bottom of the car, except pick up dropped screws.

The bottom bracket bolt, and the top, I did with a 1/4 inch ratchet and NO extensions. I did not remove the fan shroud either, but it would have given me a little room with my big hands. Now that you know where the bottom bracket bolt is, just feel for it with the ratchet and tighten it up. You just have to screw the bolt in before putting the manifold back on, you cannot start it with the manifold in place. I made a mistake and tightened it down first, which meant that the bracket was too high and the manifold wouldn't fit in place.

The top bracket bolt is just put in by feel, and then tightened, before tightening the bottom bolt. Do the dipstick bolt after so it is not in the way.

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My name is Klaus and I am a V♂lv♂holic

Klaus,

Thanks for the tip. I will use your method but with fan shroud off ;) Volvo service manual always states to remove fan shroud first ....

Ching-Ho Cheng
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1995 855 NA, Bilstein Strut & Shocks, Volvo Protective Grill, K&N Filter, E-Code Lens, ClearCorner Light, Alpine CD-Changer, AutoDim RearView Mirror, 6000K HID