Piston Blow By & Oil Seal Question?

[russelld]

My VHPD is running rather sweetly, it is a bit gutless below 3k rpm but that is normal for these engines with the Lotus ECU, it then produces quite good torque up to 7.5k rpm where it flattens off. Rolling road results from a day at Monster motorsport over a year ago showed max torque of just over 140 lb/ft and max power of 181 horses.

 

The engine seems to run with exactly the same characteristics now as it did back then when it went on the RR, it uses about half a litre of oil every 1000 miles and always has in the 2 1/2 years I have had the car. The engine does not smoke at all. The exhaust pipe exits have always been black and sooty, I put this down to the ECU overfueling the engine for safety reasons.

 

I recently did a compression test on the engine.

 

Here are the results :

 

COLD ENGINE : 12.8 / 14.0 / 13.8 / 12.4 as you can see 1.6 bar difference between no 2 & no 4 or 11.5% of the highest reading.

 

I'm not sure that I cranked the engine for exactly the same number of revolutions for each cylinder although it was close.

I made a much more concentrated effort for the second ( warm ) test.

 

WARM ENGINE : 13.6 / 14.2 / 13.8 / 13.3 a lot closer this time only 6.3% differential !

 

I was pleased with the above results.

 

The reason for my post is that my engine is leaking oil and I would like some advice on what my next course of action should be.

 

The leak is definitely engine oil and is coming from the joint between the engine and bell housing I'm 99.9% sure it's the rear engine oil seal.

 

I have had the seal replaced twice recently, the first time was when my gearbox came out for repair and it was done again shortly afterwards as it was leaking worse than before ( It has had a very slight misting of oil in this area for a long time so I decided to have the seal changed when the gearbox was removed ).

 

I have read as much as I can find on the subject and it seems that high crankcase pressure can cause the oil to be blown past the seal.

 

I have checked the steel gauze under the rocker cover as this has been sited as a possible cause of pressure build up if it gets clogged with sludge. The gauze is very clean and there is no sign of anything that would cause a restriction. The breather pipe which comes from the rocker cover and goes into the airbox is also clear so no restriction here.

 

If I have a problem and my engine is producing blow by would this be more than the crankcase breathing system can cope with thus causing pressure at high rpm ? If this could be the case is there any way that I can check or test for this ?

 

Any help or advice will be be much appreciated.

 

TIA Russ.

[Martin R]

Russ what you need to do is this. Modify the dipstick tube at the bottom. It has a plate on that bolts to the engine block. You need to drill this and get a small ( 5mm ? ) pipe braised in to act as a crankcase breather. Join this with a rubber tube to the breather on the cam cover. Should be job done. Ah i have found it.

 

http://forums.seloc.org/viewthread.php?tid=343317&page=1#pid5808257

[russelld]

Thanks Martin,

 

Someone has pointed me to this on Seloc. Very interesting ! I think I will do the mod as it can't do any harm and looks quite easy.

 

Russ.

[John FISH Curtis]

Couldn't you just link the top of the dipstick tube to the cam cover breather?

 

Remove the pipe from the dipstick tube to check oil level?

[Martin R]

John, no reason why not except the end of the dipstick tube might be a bit low in the sump ? It also could become a pain when checking the oil. Apparently if you get blow by really bad it will pop the dipstick out. I suspect VHPDs are more prone to this due to the forged pistons. They slap when cold due to the looser fit in the bore.

[jimbo07g41]

I think the idea is to reduce the pressure nearest to the crank and this is why they use the bottom of the dipstick.

[russelld]

A guy on Seloc has suggested using the second cam cover outlet to effectively double the amount the crankcase can breath, I think this would have a similar effect to the dip stick tube mod.

 

The hole on the inside of the cam cover to this second outlet is only about 1mm in diameter. The idea is to drill this hole out to 8mm and then plumb the outlet into the airbox. This outlet is currently T'd into the charcoal canister purge line on my car, I have no idea why ??

 

What do you reckon ?

 

taken from Seloc :

Quote:

posted on 27-9-2012 at 06:31 PM you may also drill out both vent opening on the cam cover. Many covers have only one of the stubs drilled through. I think mine are drilled to 8 and 10mm if I remember correctly. This provided enough venting for the blow-by of a supercharged Rover K with a broken ring land. Crank seal took no hit. Marko

 

 

Yes I can see that this would work !

 

I have just checked mine & the second vent only has a hole of about 1mm dia on the inside of the cam cover. The pipe from this vent joins into the charcoal canister purge line !!

 

I pressume you drill out the 1mm hole to 8mm vent this into the air box & block up the T into the purge line ? ?

 

I cant understand why this second vent is plumbed into the charcoal canister purge line ??

[Martin R]

Not sure on this one Russ. It may well be smaller for a very sound reason ?