Compression test result - comments please

[shn7]

Well as advised following a suspected crankshaft oil seal failure I’ve done a compression test and here’s the results:

 

Cyl 1 2 3 4

Dry 215 216 220 212

Wet 255 278 242 246

 

What do you think to these figures? The dry ones seem to be fairly consistent to me but the Cyl 2 wet figure seems high compared with the others. what does all this mean 🤔

 

Steve.

[Peter Carmichael]

Means you overdid the wet on #2?

 

Blowby would have to be astonishing to blow a seal and would show up on a dry compression test. Your numbers look fine. The problem has to be something buggered up in the breathing department.

 

The reason you run a wet test is to determine whether any gas escape you have is from the rings or past the valve seats. The fact that the wet compressions are higher indicates that any blowby you have is past the rings, but the dry numbers look perfectly fine.

[Roger King]

I don't know which engine type you have, but these figs are pretty good unless you've got a very high C.R.

 

The dry figs are nice and even. By wet, I assume you mean that you've squirted some oil down the bores? Oil in the bores is sometimes a useful diagnostic tool, but it is an artificial situation and it may be that some bores got more oil on the rings than others.

 

The real world figs are great though, so it doesn't seem like you have a problem. Poor compression figs are most unlikely to lead to a seal failure unless you also have a blocked engine breather. In fact, even a healthy engine can suffer seal failure if the breathers are blocked.

[shn7]

Peter,

 

You may well be right about the wet on #2 as I didn't use a measured amount of oil, just poured some in.

 

Roger,

 

Thanks for the re-assurance. It's a 1.8K Series SuperSport for reference.

 

So from both of your comments the thing to do next is check the breathing. I have one breather coming from the top of the dry sump tank and two (2) from the cam cover. All go into the catch tank. I'll remove the pipes and check they are clear. I suppose I should also remove the cam cover and check internally where the breathers are fitted. Any other suggestions on what else to check before taking the engine out to replace the seal 🤔

 

Steve.

[Peter Carmichael]

Now that is interesting. A dry sump has a scavenge pump removing volume from the internal spaces of the engine. A breather on a dry sump system will usually only breathe inwards.

 

Whose dry sump system are you running? You don't sound like you are running a standard Caterham system with that breathing setup, so you'd better come clean and tell us EXACTLY what DS components you have fitted.

[Peter Carmichael]

And why is the crankshaft oil seal failure only "suspected"?

[Jason Plato]

The rear oil seals on the K do pop out anyway . The procedure has now been ammended to include a 1mm bead of sealant to help secure the seal in place

 

You can actually see the seal if you look up through the bellhousing at just the right angle . Sometimes you can see the lip has moved .

 

Dave

[shn7]

Peter,

 

Std 1998 spec Caterham DS setup with no (AFAIK) modifications. Seal failure is only suspected as I know I have oil weeping from the joint between the engine and bellhousing but haven't taken it apart yet. The oil must be coming from somewhere within the area enclosed by the bellhousing as there's no signs of oil anywhere else. I've run the car up whilst on stands and watched it start to seep from the joint so am certain it's not running down the outside from somewhere higher up. That IIRC leaves the crank seal and the front end of the gearbox as possible sources for the oil. I doubt it's from the g'box as that's newly rebuilt by Road & Race and has Redline MTL in it. The oil that's leaking out doesn't have the red colour of the MTL.

 

Dave, I don't think there's anyway I can see into the relevant area with my set up but will have another look.

 

Steve.

[shn7]

Another quick question. When refitting the cam cover must a new gasket be used? Should any sealant be used or just tighten down onto the gasket?

 

tks.

 

Steve.

[shn7]

OK I've now checked that the breather pipes are clear and removed the cam cover to check for blockages inside. All clear as far as I can see. The cam cover does have two bits of rolled up wire gauze in the channels leading to the breather pipes. Is this normal? Pictures here and here.

 

Steve.

[davidvoas73]

The wire gauze is normal - suggest you clean it now you have it out.

 

I have a 2001 1.8K SS with Cat DS, I have 2 cam cover breathers which should go back into the inlet manifold or plenum (they no longer do this as I have converted to Throttle Bodies - I blanked one off and redirected the other to the airbox) The only breather on the DS system goes as you say out the top of the tower into the catch tank.

 

Your set up sounds a bit peculiar - have you got photos of the breathers?

 

Edited to say - Haynes manual for Freelander recommends replacing the cam cover gasket, however I have had the cam cover off several times and have not needed to replace the gasket or use any sealant .

 

Edited by - wavydavy on 4 Aug 2004 19:43:10

[Rob Walker]

I was plagued with what I thought was a weeping rear crank oil seal. I formed the view that it was due the vacuum remaining after the engine was shut down pulling the seal inwards. Well it wasn`t before you blame the rear crank oil seal do a simple test, stand the dry sump tank on the bench leave its pipes connected but set them pointing verticle and fill the bell tank with oil and leave it to stand for a couple of days, my problem was a porous casting and it weeped from one of the through holes for the bolts that attach it to the gearbox. The belltank had to be ultrasealed to cure the problem. I must add that I had replaced the crank oil seal twice before finding the true fault and tried running with the engine vented and sealed. If you remove the sump pan its possible to have a fairly good look at the crank rear oil seal and determine if the oil is coming from that area, if its leaking the back of the flywheel will be covered with oil.

[Roger King]

Second Peter's comments about dry sump breathers sucking air in rather than blowing it out. I had assumed you were wet sump. A dry sumper will only breathe out if it is very sick and a seal will only fail in this way if excess pressure is trapped in the engine.

 

It's not unknown for seals to simply fail because they get some abrasive dirt on them. Have you had an 'off' at a track day? As also stated, K seals are prone to moving and need to be fitted with some sealant

[shn7]

wavydavy,

The breather set up may be different from std. as the engine whilst being a supersport is fitted with the VVC plenum. The whole thing is as it was when I bought the car (used) from CC with three pipes going to the catch tank: 1 - from top of DS tank and 2 from the cam cover. Thnks for the re-assurance on the gasket.

 

RobW,

Will check carefully for leaks in the casting, though I don't this is it. Was your problem there from new? This is a six year old setup so I doubt it would suddenly become porous.

 

Roger,

The failure due to abrasive dirt could well be the answer as before re-installing I changed the flywheel and cleaned (carefully I thought) around the area. So I may have disturbed something and caused the problem myself.

 

Steve.

[robmar]

sorry to go slightly off topic but why if dry sumps should only suck via the breather, do you get oil in the catch tank

[shn7]

Rob,

 

I don't think that's off topic, just a good question.

 

Steve.

[Peter Carmichael]

The oil in the catch tank comes from the breather from the top of the dry sump tank. The breathers on the engine only breathe in.

 

With the arrangement Steve has, the evacuated fumes are recirculated to the crankcase via the catch tank. With the wavydavy arrangement, fresh air is breathed in and the fumes vent at the catch tank. There is a larger net throughput of air with this setup, but there is better evacuation of combustion by-products.

 

Sahf London;

every 1st Wednesday from 19:30 at The Duck just around the corner from Clapham Junction station

[robmar]

aha - I took the comment of

 

A breather on a dry sump system will usually only breathe inwards.

---

 

to generically mean all breathers in the system not just the ones from the engine

 

rob

[shn7]

Interesting to see Peter's explanation here. Whilst I have the two breathers from the cam cover going into the catch tank, there is also a blanked off tube on the back of the VVC (remember this is not a VVC engine) plenum.

 

Should I leave well alone or is there a good reason to change the arrangement so that the cam breathers connect to the plenum?

 

Steve.