Hi All,

I have a newly built engine with dyno time only. It came off the dyno leaking from the weep hole in the bellhousing, and I assumed rear main. I had a shop replace it, and they let it idle for 30mins or so and it did not leak.

I got it home, and it did not leak at idle, but did if revved.

The same shop replaced it for me again, and they tested it under revs - again all clear.

A few months later, I have started the car to give it as run, and after warming it for a while, it’s leaking from the weep hole.

Perhaps it is the half moon seal?

The engine has a Boundary pump with 78psi (3shims). Is there any chance the higher pressure pump is affecting the seal?

Any ideas welcome (this is so frustrating!)

 

Make sure they are putting sealant on the flywheel bolts.

Bill

 

sounds very frustrating. How much was done in the rebuild?
Was the crank tested for trueness? Was it polished? Is the rear boss on the crank true?
Maybe scratches or a lip built up on the crank where the seal runs?
Perhaps the seals are all bad? Factory oem or aftermarket?
If the half moon retainer were at fault it seems like it would never stop leaking once it started. (Sounds sort of like you are thee, actually, since idle is not much of a stressor.) But it's worth removing it, cleaning it up and inspecting it carefully for a crack, and for how circular the bore is.

Oil pressure should not be a problem, it is in contact with the sump, not the pressurized channels in the block.

 

I second the flywheel bolts, they go all the way through and you have to use silicone.

 

I’m not sure what was done to the crank for the build. I had ARP main studs installed, and the block was line honed for this.

The seals have all been OEM Mazda.

I did the first flywheel install and used red loctite. I don’t know what the shop used for 2nd and 3rd. The do lots with these cars and flywheel install should be routine.

 

Did you ever find the cause for this?

Literally have the same issue. Complete rebuild with high comp pistons, all new oem seals, boundary oil pump. Can't get the leak coming from rear main seal area fixed. Had gearbox off and went through 4 different seals (oem & aftermarket) so far. Still leaking. Every time the shop tests it and has the engine running for a while it seems to be dry so it's also related to prolonged higher rpm / load.

Just had the engine pulled, checked, new half moon seal + hold/cover plate.....




And it's still leaking....
This is driving me mad.

 

The fourth seal on mine was put in with a ‘speedy sleeve’ on the crank. It does not appear to be leaking now.

Previously it would leak when revved but not at idle. Now it is not leaking when revved. I’m not calling it solved yet and until I’ve been able to put some miles on it.

There was no visible or tangible damage to the crank surface.

That’s the update for now.

 

There are a 3 reasons that cause rear crank leaks with properly installed rear main seals. The first is two much crank case pressure, the second is not sealing the flywheel bolts and the last is a leaking seal carrier/pan. A speedy sleeve will increase the normal force on the lip of seal because of the increased journal diameter.

 

Thanks for the update. According to the mechanic the current seal was sitting much tighter with the new/used replacement seal holder plate. But alas, still leaking.
Going back and getting tranny of again today. We shall see...

 

Update: Mine is still leaking. Not sure what to do now, other than go back for the pan seals.

 

Update on my end
It's been dry now for a couple of weeks. Fingers crossed.. Two issues after the latest repair job.

• An aftermarket rear half moon seal was installed. These are like half a mil longer than oem mazda seals at the ends, causing the seal to twist and move outwards after installation. This was causing a fresh leak by the rear main seal area....
• The front sealing plate on my 6-speed gearbox had lots of wear / damage from a previous catastrophic throwout bearing failure. The shaft area where the bearing sits on was worn down almost a mm. A new oem front plate wasn't available in time so a cracked front plate from a broken 6 speed got welded and installed during the last rear main / half moon seal repair. It didn't hold up and was also leaking.

So (hopefully) the tl;dr for my issues:
Rear main bracket cover sealing surface was worn down, replaced with a used part. This made rear main seals finally push in tight, not immediately slip in without effort. Victor reinz aftermarket rear main seals are also slightly larger diameter than OEM and were therefore used. Half moon seal issue was also suspected and replaced with new oem part. Still bone dry after 60min on track and 700km.

 

The speedi sleeve mentioned earlier did not help, and the car is back in the shop. The engine builder has requested compression and leak down testing, pressure gauge on the crank case when running, smoke machine test on the crank case and measure of the crank surface seal runs on for ‘PCD’ (by which I think he means eccentricity).

I assume these would precede pulling the engine for a year down and measure, as there seams little point in trying a 5th seal.

 

And mine resumed leaking also. gg wp.
With the 1l/1000km oil consumption on top it's also looking like another engine pull and complete disassembly. Someone fucked up. Either the machine shop or engine builder. :(

 

Most turbo Miata engines leak a small amount from the weep hole in the bell housing. I have been through this with mine. Mine was mostly leaking from the flywheel bolts. I had originally used blue Loctite. When I resealed the bolts I used red loctite on the threads and a small amount of silicone sealant on the back of the flywheel around the through holes and under the bolt heads. This reduced the leakage to a very rare occasional drip from the weep hole. Sealing the pan and seal carrier is a difficult proposition. I used the right stuff sealant which is one of the best and used plenty. I knew before hand this was a problematic area of this engine.

 

actually most Miata engine leaks

 

Really? My other car is fine and has been perfectly dry for 10 years+

Update on the leaker: compression test on the brand new engine shows one cylinder that is way way down on compression, which explains the leaking rear main. Insert sad face here.

 

I’m going to edit my previous post. What I meant was most turbo Miata engines leak. I have never seen one that doesn’t leak. Valve covers, rear main or oil pan.

 

For the record LeoNA, I thought your post was balanced and objective.

 

I am also following, I have a fully built turbo miata and I am having my rear main seal leaking as well, about to pull the engine here soon and try to fix the leak. I'll update if I find a solution!

 

this is great info - silly question, how do you go removing the bolts after applying red loctite? i thought it was "permanent"...