10 replies to this topic

[Dannyboolahlah]

The engine is a 998, ran okay before, but not great, I put that down to the carb needing a tune up.
Its now supercharged with a VMAXSCART kit, but was running badly with the vacuum line attached to the servo and breather. With both connected the servo didnt get any vacuum, with just the servo connected its fine but theres quite a lot of smoke/fumes coming out the breather pipe.

Before fitting the decompression plate, I was getting around 145psi in each cylinder when dry, I didnt think to test it wet as I didnt suspect anything wrong.
Now I have 100-110psi dry and 135-145psi with a splash of oil.
Am I right in thinking this indicates the piston rings are shot?
Would it be completely idiotic to just plumb the breather into a catch tank and filter and ignore the issue till next winter? As theres a good chance itll be coming out for a 1275 by then.

Thanks.

[Spider]

The Crankcase Breather shouldn't connect directly to Vacuum, it should be connected, in your case, via a PCV.

 

I was asked a little while back to have a look at one of these VMAXSCART Kits as the installation instructions were lacking in some of the finer points. For the most part, the kit seem to be 'mostly there' but some of the refinements are missing I feel, like what ignition advance curves should be used (for example, this kit was supplied with a Weber carb and yet is was recommended that a 'distributor with a vacuum advance' should be fitted) and relevantly here, there was nothing in regards to Crankcase Breathers, how the should be fitted and plumbed.

 

You will usually get some fuming from the crankcase and for a road car in particular, it's best if these can be drawn in to the Inlet tract in an appropriate way, and this is probably more important with boosted applications like yours.

 

The Compression tests I wouldn't get too hung up on but at a glance, appear a little on the low side and possibly show some wear. The reason I wouldn't get too hung up on them is they don't represent how the rings behave & seal under running conditions, they are little better than a leak down test.

[Retroman]

yep the breather and servo should not be connected together 

 

The manifold vacuum should be for the servo

 

The breather should go in somewhere upstream of the butterfly, or to air or use a PCV into the manifold.

 

Is there a vacuum for the dizzy too ?

[Dannyboolahlah]

Theres one 9mm ish for the servo, and one 2-3mm ish for the dizzy.
The 9mm is before the charger rotors, the 3mm is after (also used for a boost gauge), asked VMAX to confirm this was correct, and he said its not an issue.

Ill have to rethink the breather then, may have to ditch the PCV and just go for a catch can and filter.

My main concern though, is the smoke coming out the breather.
Found someone on here suggesting the rings could be gunked up and redex into each bore could clean it up. Its a possibility as I did clean up the piston tops when the head was off. I put some grease at the top of the bore to catch the rubbish and then moved the piston to TDC, cleaned it then wiped the dirty grease away, but its possible some got past. Just hope I havent done too much damage.

Edited by Dannyboolahlah, 25 April 2018 - 05:54 PM.

[minimans]

Is the smoke drifting out or pumping out? If the rings are bad it would pump out the breather like a smoke stack If it's just drifting out I would suspect it's just oil vapor and possibly the vent gauze is no longer there?

[Dannyboolahlah]

Is the smoke drifting out or pumping out? If the rings are bad it would pump out the breather like a smoke stack If it's just drifting out I would suspect it's just oil vapor and possibly the vent gauze is no longer there?

Im not sure which Id describe it as. Theres quite a lot, but I dont think its under much pressure.
Im on holiday at the moment. I will get a video when Im back at the weekend.

[Spider]

Theres one 9mm ish for the servo, and one 2-3mm ish for the dizzy.
The 9mm is before the charger rotors, the 3mm is after (also used for a boost gauge), asked VMAX to confirm this was correct, and he said its not an issue.
.

 

The 9 mm port for the servo makes sence.

 

The other one though? It can be either under vacuum or pressure (when on boost). When under boost, it will damage the vacuum diaphragm, no question. It will also give a full vacuum at idle too, that will likely lead to over-heating while idling.

 

Considering a N/A application and the Carbs used with them, the Vacuum Port on the carb is located such that there's no vacuum on it at Idle and then comes in progressively as the throttle is opened, it isn't the same as manifold vacuum. Some of the HIF Carbs have a port closer to the manifold for the advance, however, they are plumbed via a temperature valve and not directly.

 

There is a post on the forum regarding and showing just this.

 

<Edit: http://www.theminiforum.co.uk/forums/topic/318946-vacuum-advance-fitting/   >

 

 

Edited by Moke Spider, 25 April 2018 - 07:41 PM.

[Dannyboolahlah]

Ok, thanks for your reply. I was told boost at the dizzy wouldnt be an issue. I knew it wasnt an ideal set up, but didnt want to pay out for distributorless ignition quite yet.

Im more clued up on more modern fuel injected engines, the mini is my first classic. But my understanding was that the dizzy should get full vacuum at idle, then as the throttle opens the vacuum decreases until there is no vacuum at full throttle and you get full ignition advance. Is this not the case?

[Dannyboolahlah]

Just read through the thread you linked to.
So the vacuum advance works the opposite way to what I thought?

[Spider]

The Vacuum for the Vacuum Advance will 'rise' and then 'fall'. It will tend to be at the highest Vacuum around 2000 - 3500 RPMs at light throttle, like you would be when 'on the cruise'.

 

For now, I'd suggest disconnecting it and plugging the S/C Port.

[Dannyboolahlah]

So. Im back in the country and had a fettle today. And happily all seems well!
Tried the redex in a hot cylinder trick, but to be honest Im not sure it did anything as it wasnt too bad before I did it.
Either way, I think its just oil vapour as suggested and I may have overreacted a bit!

Ive ordered a catch tank and filter to take care of the breather, and some spark plugs etc to give it a good service then Ill get it on the rolling road.
Still need to have a rethink with the dizzy though.

It looks like Minisport is the nearest place I can get it setup, but its still about 35 miles away. Not sure i want to risk damaging anything on the way there so Ill probbaly look into borrowing a trailer, and maybe a driver as Ive never towed anything before haha. Although my basic license just about covers it and I have a tow bar on the van.