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Mystery oil leak from oil pump/rear balance shaft area?

Old 12-02-2018, 11:37 AM
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Icon5 Mystery oil leak from oil pump/rear balance shaft area?

Okay, first off, welcome back to me as I have been a ghost here for ages. This about my 12th Honda out of about 2 dozen cars so far . . . been busy maybe? Anyway, I bought this one to teach my wife to drive stick, as the transmission feels fantastic despite 165k miles on the odometer, and I wanted to take it to some track days just to get some FWD experience, something different for me to learn to drive fast.

Anyway, I am the proud new owner of a green '99 Prelude base model 5MT. Car runs great in every manner, has a bit of vibration which I figured at this age is probably due to parts store replacement engine mounts rather than factory, namely the OE hydraulic mount, but whatever. It's not bad, and I didn't buy it to be perfect. What IS wrong with the car, however, is that it loses oil, and quickly. Like, I've driven it 160 miles so far and I've added a couple quarts to it. It drips and makes not quite a puddle but at least a small oily area when parked, and that area is right under the front (driver's side) of the motor. When I looked up there, I could see oil mess on the lower timing cover outside, as well as the rear of the oil pump and water pump area, and oil droplets hanging from the oil pan on the driver's side and oil that had hit the lower control arm pickup on the chassis, with a few drips coming from there. The inner CV boot is also plenty wet, but doesn't drip, probably because it flings any oil off of it - probably how the lower control arm pickup point gets oil on it.

Anyway, I've got it stripped all the way down now, missing all timing gears and everything, and I couldn't see where oil would be coming from. There was oil everywhere, it had gotten all over the balance shaft belt, but not really on the timing belt - only the edges were a tad wet, the rest of the timing belt was dry. There was a lot of oil up under the water pump and on top of the oil pump/rear balance shaft housing, but the cam seals look good. Everything from the front balance shaft to the back of the motor and from above the timing tensioner down to the oil pan was wet and caked with black gunk; it looks like it got oil onto the balance shaft belt and got flung everywhere.

Also, the rear balance shaft has seized; I don't know if that helps or hurts its little gear box's chance of leaking at its seal, but that doesn't look like it's designed to be serviceable. There's no RTV around the rear balance shaft housing, so it's not obviously idiot-assembled from the outside.

The motor looks like it has been rebuilt at some point because there is silver paint on it that comes off when I hit it with brake cleaner, and it appears to have been applied after assembly. The oil and and oil pump have also obviously been replaced; the RTV is gray, but it's nowhere near as even and professional looking as Honda's work.

A few photos attached for giggles, but not very helpful as the mess inside was everywhere, every nook and cranny covered in gunk and wet with oil.


Front cover lets you know some stuff wasn't all too good in there


Mostly cleaned up now, but nothing obvious


Mostly cleaned up now, but nothing obvious

So, to the question - is the oil pump hard to reseal, or is there a port or hole somewhere that gets weak or leaky? Maybe whoever did that screwed up? This thing loses a lot of oil, a lot more driving than what it loses running when parked. I think I'm going to need to pull the oil pan and oil pump, but I wish I knew what the problem was before I go resealing things on a maybe. It's just hard to tell.
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Old 12-04-2018, 09:30 AM
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Default Re: Mystery oil leak from oil pump/rear balance shaft area?

Hard to really tell there, but I would go ahead and do the oil pan, valve cover and spark plug tubes, cam seals, front crank seal, and the front balance shaft and the gasket for the rear balance shaft assembly, even if you are leaving them disconnected.

How is the compression and valve seals, aka is it burning a bunch of the oil internally?
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Old 12-04-2018, 03:27 PM
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Default Re: Mystery oil leak from oil pump/rear balance shaft area?

I left it apart for a few days and thought about it. I figured I'd have to just put the timing belt back on, put the balancer belt pulley and harmonic balancer back on the crank, and drive it around a bit now that it's all cleaned up and see what looks leaky after a modest drive.

But then I started thinking, it flung oil around, but only around the lower half of the timing area, and it didn't get all over the timing belt. So that kinda means it's on the plane of the balancer shaft belt. The thing with oil nearest the balancer shaft belt is that rear housing. The rebuild shop probably didn't do much if anything with that, since it's not very serviceable. So I had time today and I pulled that housing, and I discovered a few things:
-The lower bolt hole was stripped, able to remove by hand,
-The gasket had never been replaced, and
-The shaft in the housing is frozen, but the balance shaft is FINE in the block.

So what I should be looking for then is a new/rebuilt/replacement housing and a new gasket for it. I could separate the gear from the shaft and go find a new bearing and seal for it, but it looks like I can get a rebuilt housing for about $100, and then I don't have my block sitting open for days while I mess with it. Maybe either way, but I'm 99% sure that that stripped bolt hole and crusty old gasket were the problem. I'm not sure if it's possible that the seizing of the shaft caused that bolt to rip out, but otherwise someone just overtorqued it and called it a day. Anyway, 1 M8 helicoil and a new gasket, coming right up!
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Old 12-04-2018, 03:29 PM
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Default Re: Mystery oil leak from oil pump/rear balance shaft area?

Originally Posted by snobordboy View Post
Hard to really tell there, but I would go ahead and do the oil pan, valve cover and spark plug tubes, cam seals, front crank seal, and the front balance shaft and the gasket for the rear balance shaft assembly, even if you are leaving them disconnected.

How is the compression and valve seals, aka is it burning a bunch of the oil internally?
Thanks dude. Nobody else even had a suggestion. I'll try the helicoil and gasket, and if I have to tear out all that relatively fresh gray RTV on all those components I will I guess, I just won't be happy about it! Motor has obviously been rebuilt already, maybe 20-30k ago if I had to guess by the looks. Cam and crank seals look really good.

Also it doesn't smoke at start-up at all, even after sitting for days, and it doesn't smoke when you rev it up and make a full throttle pass, so internally it's gotta be decent.
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Old 12-05-2018, 07:15 AM
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Default Re: Mystery oil leak from oil pump/rear balance shaft area?

Yeah, if you have some issues with that rear balance shaft "gearbox" It could be a fairly easy fix. I am usually on the point of replacing stuff if it is apart, but there is a lot to be said for leaving it alone if its in good shape, especially with the engine in the car.
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