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Mythbusters time - Oil pan and motor mounts

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Old 12-06-05, 08:59 PM
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Mythbusters time - Oil pan and motor mounts

Hey everyone -

Just stripped down an FD long block this weekend, and learned a LOT. I have a BUNCH of pictures to go through to document everything - keep your eye on ClubRX for some big writeups .

Anyhow, tonight I was in the garage examining parts and trying to straighten up a bit. One thing I wanted to look at was how the motor mounts bolt to the rear iron.

I have only slightly participated in re-sealing an FD oil pan - I've never done one personally. But, more than one person had trouble with oil dripping from the motor mount bolts after installation. I believed that the motor mount bolts went into a pressurized oil passageway, so they needed to be sealed up good with RTV.

Well, I did some looking and experimenting with the motor I just took apart. I flipped the rear iron housing upside down and cleaned the junk out of the motor mount bolt holes. Then, I squirted a small puddle of PB Blaster into each hole and let it stand for 5 minutes. The level of PB Blaster stayed the same, indicating that the hole is just by itself and not connected to any oil passage. If you've ever used PB Blaster, you know that it seeps into the TINIEST cracks.

So, it seems on this motor at least that there's no correlation. I see 3 options -

1. On some motors, the bolt holes go into an oil gallery, and on some they don't.

2. It's all just bunk - all the bolt holes are sealed, and people are just imagining things.

3. People goop too much RTV on the bolts, which put pressure on the rear iron, causing a small crack into an oil gallery.

Anyone with other insight?

Attached is a bad closeup pic of the hole - you can still see a tiny amount of PB Blaster in there .

Dale
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Old 12-06-05, 09:21 PM
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I think it has to do with just the proper sealing of the oil pan and the oil just starts to trickle down to where the motor mounts are. That's my guess. BTW, when I had oil leaks from my engine it was around the turbo side and also a bunch of oil and gunk around the motor mounts.
Once I sealed it up with RTV and dimpling, no more oil leaks. But who knows.
If you're going to do some type of engine R&R or related write-up, let me know. I can provide you with pictures of my engine R&R. I'm too lazy to write it up myself...
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Old 12-06-05, 09:44 PM
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It's called improper torquing of the bolts. When the bolts are improperly torqued, it causes the oil pan sealing surface to distort and break the seal. As a result, oil leak.
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Old 12-06-05, 09:51 PM
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yep

Basically the mounts just help seal the pan. I was told by friend who had his FD repaired at PFS that the drivers side mount has a small raised area that helps to hold the pan in place. This statement might not be 100% accurate but that's how I remembered it being explained to me. Basically if the motor mounts are not placed on the car correctly this can also cause a leak.

It seems to me that sealing the oil pan correctly is practically an art form as is most any type of mechanic work on an FD LOL



Originally Posted by chillin_rx7_guy
I think it has to do with just the proper sealing of the oil pan and the oil just starts to trickle down to where the motor mounts are. That's my guess. BTW, when I had oil leaks from my engine it was around the turbo side and also a bunch of oil and gunk around the motor mounts.
Once I sealed it up with RTV and dimpling, no more oil leaks. But who knows.
If you're going to do some type of engine R&R or related write-up, let me know. I can provide you with pictures of my engine R&R. I'm too lazy to write it up myself...
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Old 12-06-05, 10:30 PM
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theres 2 problems with the fd setup.

1. the motor mounts bolt thru the pan, and thus vibrations and torque gets transmitted thru there. notice 1st gen pans rarely leak, even after 20years? while the fd was leaking under warranty.....

2. the pan bolts need to be sealed to the pan with the pan, if you put em on seperate, it wont seal well. torquing the bolts has an effect on the seal of the rear of the pan.
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Old 12-06-05, 11:05 PM
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Originally Posted by j9fd3s
2. the pan bolts need to be sealed to the pan with the pan, if you put em on seperate, it wont seal well. torquing the bolts has an effect on the seal of the rear of the pan.
Yep. I always wondered if Mazda (or whoever does the remans) actually bolts up a set of mounts to seal the pan for a day or two, then removes them to ship it out (since mounts don't come with the remans). Or, if they just do a have **** job and seal the pan without the mount bolts.

Another thing to help is to add some RTV around the outside hole of the motor mount bolt. So as the head of the bolt contacts the mount, it will help seal it up too. Just don't get any in the thread of the hole, it will tear up the threads if you try to bolt it up with that junk in there.
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Old 12-07-05, 05:01 AM
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here is what I have noticed. All the above mentioned plus a little bit extra on bolt torque. After you torque down the mount bolts, You MUST go back and re-torque the 10mm head bolts that go around the pan.

Every pan that was leaking the perimeter bolts( directly behind and to the side of the mount bolts) were finger tight or even backed out a few turns. So my procedure is to torque the perimeter and then the mount bolts. Then, back around the perimeter bolts. It has worked welll for me so far.No leaks after the repairs.

Also it is very important to have the oil pan lip/sealing surface flat. When overtorqued prior, most are wavey and will not seal well.
Dave
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Old 12-07-05, 06:00 AM
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Originally Posted by Fritz Flynn
yep

Basically the mounts just help seal the pan. I was told by friend who had his FD repaired at PFS that the drivers side mount has a small raised area that helps to hold the pan in place. This statement might not be 100% accurate but that's how I remembered it being explained to me. Basically if the motor mounts are not placed on the car correctly this can also cause a leak.

It seems to me that sealing the oil pan correctly is practically an art form as is most any type of mechanic work on an FD LOL

This is true, the driver's side (aluminum) mount has a small "nub" on it that pushes against the pan. It takes the place of a pan bolt. On the steel replacement mounts that Mazda sells the nub has been removed. It is necessary to install a spacer sandwiched between the mount and pan to stop a huge oil leak.

We install a set of mounts for a day prior to shipping engines back to FD owners, to allow the RTV to seal the pan in the correct fashion. I do not know if the Mazda reman facility does this also.
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Old 12-07-05, 08:27 AM
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VERY interesting stuff!

So, we've de-bunked a few things:

1. You do NOT need RTV on the threads of the motor mount bolts. BTW, the motor I just took apart had RTV CAKED on the threads. But, some RTV around the motor mount holes on the outside is a good idea.

2. To properly seal, the RTV needs to dry with the mounts attached.

I'll have to investigate the motor mounts in my garage and look for that dimple - that's interesting.

BTW, has anyone tried the oil pan gasket to any great success? I know most people just use RTV - dunno if the gasket would help or hinder.

Dale
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Old 12-07-05, 09:07 AM
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Originally Posted by DaleClark
BTW, has anyone tried the oil pan gasket to any great success? I know most people just use RTV - dunno if the gasket would help or hinder.

Dale
IMO, using the gasket is an almost certain path to an oil pan leak. Almost anything non-metal will stress relax over time. Therefore, anything that prevents direct metal-to-metal contact under the motor mounts will result in the mount bolts working loose, followed shortly by the pan losing its seal in that area, and finally, a leak.

The same is true - you mentioned this - if the pan is sealed and the sealant left to harden w/o the motor-mount bolts torqued. This would leave a layer of sealant to stress relax, very similar to what would happen using a gasket. It would be difficult to torque the bolts w/o the engine installed (as in a rebuild) and then remove them so that the engine could be installed with other motor mounts, without breaking the seal in the bolt areas, since the pan would flex and break itself loose.

The best way to do the sealing would be to torque the engine mounts in place and never remove them until it was time to seal the pan again.
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Old 12-07-05, 09:48 AM
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hrmm i gotta fix my oil pan so this is interesting. dunno if this helps about gaskets... but i do know the miata has NO real gasket for the oil pan, hence why it never leaks. just a bead of rtv all the war around. the only thing it does have is a 2 rubber half moons, that go under oil pump and the rear main seal. but i put a light bead there JUST to make sure. funny thing is miata oil pans have 2 pieces, the cast alum pan, and the steel splash baffle. all done with rtv.


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Old 12-07-05, 10:30 AM
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Originally Posted by Nat6c
hrmm i gotta fix my oil pan so this is interesting. dunno if this helps about gaskets... but i do know the miata has NO real gasket for the oil pan, hence why it never leaks. just a bead of rtv all the war around. Los
There's a thread in the archives that may be useful:


https://www.rx7club.com/3rd-gen-archives-73/easier-oil-pan-removal-305386/
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Old 12-07-05, 10:34 AM
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SWEET THANKS. ut i'll prolly lowert the sub frame anyway previous owner busted 1or 2 studs on the turbo mounting point and a stud on my downpipe. i'd tried to rig for the mean time to stop my exhaust leak but no luck. so i gotta pull my turbo's, down pip, gonna replace my OMP lines to braided, and fix a tiny oil leak at the oil filter neck all in one shot, so i figure it'll be easier to just lower the sub frame... anyone think otherwise?


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Old 12-07-05, 10:37 AM
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Read that page you just linked to. IMHO, you REALLY should drop the subframe to do the job. You need PLENTY of room to examine and clean everything.

Also, one thing that might help -

http://store.summitracing.com/defaul...=egnsearch.asp

Moroso sells an oil pan stud kit. Replaces the bolts with studs and nuts. Dunno how well it would work on an FD, but I used it on my FC with great results. The neatest thing is the studs have a hex socket at the top so you can torque them in with an allen wrench.

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Old 12-07-05, 10:49 AM
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Originally Posted by DaleClark
Read that page you just linked to. IMHO, you REALLY should drop the subframe to do the job. You need PLENTY of room to examine and clean everything.Dale
Dale,

That is obviously the best way to do it, but I was fairly easily able to thoroughly clean the bottom of the engine, clean out the bolt holes, etc. with the sub-frame deflected as I described and the car on jack stands. I then didn't have to realign everything when I was done.

I also have always resisted (mental defect?) disassembling more than I have to to do any job.

BTW, Dale, your humble opinions are almost always right on!

Last edited by DaveW; 12-07-05 at 10:56 AM.
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Old 12-07-05, 11:44 AM
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Originally Posted by DaleClark
Moroso sells an oil pan stud kit. Replaces the bolts with studs and nuts. Dunno how well it would work on an FD, but I used it on my FC with great results. The neatest thing is the studs have a hex socket at the top so you can torque them in with an allen wrench.
The Moroso kits works great but you'll have a few issues on the FD:

1. Some of the holes are open ended. So, if you want to use the studs here, you need to add some Lock-Tite and then let it sit for a day. You will then be able to torque the nuts without a problem.

2. The studs extend quite far to make it a hinderance to get the pan in place around the oil pick up and also onto the studs. I cut off about a 1/4" or so on each stud and it made things much easier.

I highly recommend them as it makes getting the pan lined up a snap. I imagine it would be a pain to put those in while the engine is already in the car. In that case, maybe using 2 or 4 of them would be helpful just for lining up the pan for reinstall.
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Old 12-07-05, 12:00 PM
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Here's my theory...the motor mounts are torqued to 50+ft-lbs and the pan bolts are torqued to 12in-lbs or something. GENIUS I tell you...what side, front or back leaks again?? go figure

this is what I did, learned from a guru on another board...did this to the pan and the block and used "The Right Stuff" by permatex...black can orange writing...NO GASKET
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The motor in my car is the first that I've built and I have NEVER had a drop of engine oil on my garage floor.

Last edited by dubulup; 12-07-05 at 12:03 PM.
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Old 12-07-05, 12:15 PM
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Did you just dimple the rear, or the whole pan and mating surface?

Dale
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Old 12-07-05, 12:23 PM
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Originally Posted by DaleClark
Did you just dimple the rear, or the whole pan and mating surface?

Dale
When I did mine, I dimpled the entire pan (more around the bolt-holes), but not the engine, so the raised edges of the dimples would dig into the engine as the bolts were torqued, somewhat locking the pan in place.
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Old 12-07-05, 01:31 PM
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Originally Posted by DaleClark
Did you just dimple the rear, or the whole pan and mating surface?

Dale
dimpled the entire pan and entire block, careful not to bend the edges of the pan...use a block or something to support the edges.

theory behind the dimples (pan and block) is to create something for the sealant to "dig its fingers into".
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Old 12-07-05, 02:15 PM
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Originally Posted by Mahjik
Yep. I always wondered if Mazda (or whoever does the remans) actually bolts up a set of mounts to seal the pan for a day or two, then removes them to ship it out (since mounts don't come with the remans). Or, if they just do a have **** job and seal the pan without the mount bolts.

Another thing to help is to add some RTV around the outside hole of the motor mount bolt. So as the head of the bolt contacts the mount, it will help seal it up too. Just don't get any in the thread of the hole, it will tear up the threads if you try to bolt it up with that junk in there.
mazda puts bolts in there, but no mounts. taking the bolts out and putting the mounts on makes it leak....
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Old 12-07-05, 02:18 PM
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Originally Posted by DaleClark
VERY interesting stuff!

So, we've de-bunked a few things:

1. You do NOT need RTV on the threads of the motor mount bolts. BTW, the motor I just took apart had RTV CAKED on the threads. But, some RTV around the motor mount holes on the outside is a good idea.

2. To properly seal, the RTV needs to dry with the mounts attached.

I'll have to investigate the motor mounts in my garage and look for that dimple - that's interesting.

BTW, has anyone tried the oil pan gasket to any great success? I know most people just use RTV - dunno if the gasket would help or hinder.

Dale
you dont really need to seal the threads, but you do need to seal around the bolt holes, between the pan and the block, the mounts and the pan, and the bolts and the mount.

doesnt hurt to seal the threads too.

can you imagine having to scrape the oil pan surface with studs on it? its bad enough as it is....

the older rotaries (pre rx7's) had studs and these metal support things to spread the load out.
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Old 12-07-05, 02:22 PM
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Originally Posted by j9fd3s
mazda puts bolts in there, but no mounts. taking the bolts out and putting the mounts on makes it leak....

That's what I thought - releasing bolt tension (with or without mounts) at the mount area to put on new mounts allows the pan to pull away from the sealant, creating a leak path.
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Old 12-07-05, 02:23 PM
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Originally Posted by DaveW
That's what I thought - releasing bolt tension (with or without mounts) at the mount area to put on new mounts allows the pan to pull away from the sealant, creating a leak path.
and they do.....
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Old 12-07-05, 03:23 PM
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Originally Posted by j9fd3s
mazda puts bolts in there, but no mounts. taking the bolts out and putting the mounts on makes it leak....
I don't necessarily agree with that. I've known many people to change motor mounts without causing a leak.

Originally Posted by j9fd3s
doesnt hurt to seal the threads too.
I would use "Thread Sealant", not the same stuff you are sealing your pan with.. I had some sealant get into a hole and thought it was ok. A helicoil later, I changed my mind.
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