Crankcase pressures and ventilation 1

[NickJ67]

I'm trying to reduce leakage and general slobber from a Triumph 2.5L 6 cylinder engine. Actually in a '72 PI saloon but substantially the same as used in TR5/TR6. Mid 60's engineering with accountant intervention.

As standard they have only a single 1/2" outlet from the rocker cover, going to the atmospheric side of the inlet tract. The same arrangement and sizes are used on Triumph 1300 4 cyl engine where they work better. The 2.5s are known to have slobbering tendancies, although it is probably fair to say mine is worse than usual due to being well overdue a rebuild! I'll get to it eventually.

Meanwhile, I've been working on improving this rather primitive system and aiming for some vacuum in the crankcase as is the case or more modern engines.

I've added a larger, second breather/separator onto a redundant fuel pump connection in the crankcase. This comprises of a 80mm dia x 120mm tall pot connected at its base to the engine by 20 x 40mm tube. The pot has a dished base to alow oil to drain back and a perforated partition 30mm above this with 70mm of loose packed coarse SS wool (two scouring pads in fact) and another perforated partition. The outlet is 1/2" ID and exits vertically with a further plate baffle in fron of its entrance. This is connected to the engine side of the inlet via an orifice. The orifice section can readily be changed.

The original breather is retained, but has a pcv valve added in line so it only comes into play if the crankcase pressure goes above atmospheric. The engine has proper lip seals both ends of the crank and these are new.

At present I have a temporary vacuum gauge connected to the breather pot and mounted in the car so it can be seen while driving. Having worked my way up from a 1.5mm orifice,I'm now at 3mm. This gives -6psi at idle and light cruise and about -2psi at 70mph cruise on the flat. Pressing harder results in no vacuum. The gauge doesn't read positive (something to address).

My questions:
- What is a reasonable level of crankcase vacuum to have as a maximum? 6psi at idle/low load is starting to feel like quite alot, but this engine could still do with a bit more flow when working hard. Just excessive blowby perhaps?

- Touring the internet suggests that smarter PCV valves exist offering more control over pressure/flow. However, a fairly detailed scavenging expedition to my local scrapyard didn't turn up anything more sophisticated than than simple non-return valves - some sprung, some not, presumably used in conjunction with an orifice somewhere. Ironically, it looks like the PCV valves used on 60s/70s MGs and Triumphs (not mine though) might be the way to go.

http://mgaguru.com/mgtech/engine/cv103.htm

Any other valve suggestions welcomed! I'm UK based -real PCV valves seems to be much more common in the US.

Thanks

Nick

 

[blacksmith37]

Put in a Nissan engine; My 5.6L with 112K has only traces of dust which I hose off.

 

[evelrod]

Hey, Nick....The TR is, after all, British by birth and design! It's supposed to leak. If our Lotus and Mini did not "weep" a bit I might forget and think I'm driving something the Japanese copied from the Brits!!!

Rod

 

[NickJ67]

Blacksmith,
Doubt the Nissan motor will go in the engine bay. I've previously measured for either Audi V8 or Lexus V8 - both are too wide. There might be some other matters needing attention too with >300bhp where now there is 130ish! Car only weighs about 1200kgs so it would go well though. The current engine has done about 140k and is the original 39 year old factory build, so it hasn't done too badly.

Rod,

Yeah, they do have a tendency to mark their territory. This one certainly does and resists all attempts to stop it. My other Triumph (Vitesse 2L) with the short stroke version of the same engine is actually fairly leak-tight, although I did cheat and replace the original gearbox (a major leak source) with a Toyota W58. The breather on that one is still coping - just, although that engine is also very well used.

Nick

 

[NickJ67]

To simplify the question and remove the need to read my original ramblings:

When designing a PCV system, what pressure (or range of pressures) should I be aiming to get in the crankcase?

I am not planning an engine swap any time soon.

Thanks

Nick

 

[thruthefence]

Have you considered a compression check?

Here's one guy's fix:

http://www.home.earthlink.net/~roethler/engine.html

Same engine I installing in the Lotus Europa

 

[NickJ67]

Compressions are between 195 & 200psi on all 6 after 5 strokes, engine hot. Getting about 60% of that on the first stroke. Surprisingly good.

Did a 320 mile run last night on open roads at 70-80 mph. The prototype system was holding 1 - 2 psi below atmospheric at that load and actually improved slightly over the run. Used about 1/2 pint of oil (better than usual) and no slobbering - must be doing something right.

Did a quick write up with pics if you are interested

http://sideways-technologies.co.uk/...case-breather-mod/page__pid__75002#entry75002

Some nice work on that Midget. Good engine the Toyota but not really right for my big old saloon..... Liked his "rotary silencer" reference to a turbo!

Nick

 

[Tmoose]

Drag racers in search of best possible ring seal and keeping (low octane) oil out of the combustion chambers have resorted to various crankcase evacuation schemes (in addition to cylinder finishing procedures resembling occult rituals, but with less human sacrificing.)

In the Bill Jenkins days it might be scavenging nozzle plumbed into the exhaust system .

Nowadays some take a more direct approach.

http://moroso.com/catalog/categorydisplay.asp?catcode=17200

 

[NickJ67]

Thanks for that - sent me in a new direction and a differently worded search turned up new information.

Must say I didn't know that the drag boys were actually fitting vacuum pumps, though I was aware that dry sump systems have the same effect up to a point due to the scavenge pump.

Nick

 

[patprimmer]

One caution. If you pull to much vacuum, you can boil the oil at normal operating temperatures thus causing failures from poor lubrication.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[evelrod]

Hmmmm? Just got a '72 GT-6 in my shop Sunday for a few race based changes. Battery relocation, paint and body....that sort of thing.
Funny thing...it does not leak, weep or anything. Dry as a bone. It probably was not always that way since there is a bit of oil residue in the foot well. Wonders never cease!!!

Rod

 

[patprimmer]

Are you sure there is any oil in the sump?

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[NickJ67]

Pat,

Yes, I am aware that there can be consequences like that, and also increased oil mist drop-out, potentially reducing splash lubrication of little ends and cam lobes (it's a cam-in-block engine). That was one of the reasons for my OP - fishing for info from those who might really know what is too much. This is partly answered by some of the drag-racing engine info I found once pointed in that direction. Looks like I shouldn't have anything too bad occur if I don't go beyond 6 psi. Always happy to collect other opinions on that though!

I'm not after big vacuums, more a consistent moderate vacuum over a range of operating conditions. Bit tricky with the crude system that I have now. I need to identify a suitable control valve to improve matters, although what I have now seems to be quite a bit better than nothing.


Rod,
The engine I'm working on now is the long stroke version of the GT6 one - just the psitons and crank are different. Also have a '67 Vitesse which has (or had in this case) and identical power train to the GT6 +.

Certainly in Triumph circles, an absence of oil leaks tends to indicate the component (engine, gearbox, diff) is empty! Must have been a superior build...

Regards

Nick

 

[evelrod]

Nick, our '63 Austin Cooper and '65 Lotus Cortina are both pretty "dry" but it took many tears (sorry 'bout that) of practice to make them so. This GT-6 is a vintage racer and suffers horribly from "too many owners" syndrome. The powertrain has been re done by a local member that builds and rents vintage race Spitfires within the local club. His work seems impeccable...the rest of the car pretty much suffers from the "hey we have all these TR parts lying around...Let's build a race car"!!!

A few thousand and a couple weeks in the paint/fab bay along with my part in rerouting the electrical and fuel systems should make a significant improvement. It's basically a good car that was professionally built back in the day...Just seen better days, that's all.

A "cautionary tale" to any of you reading this that contemplates buying a "race car" (or any car, for that matter)...Getting it cheap may not be the best idea, especially if you are the victim of unscrupulous venders. My firm belief is that it will always be cheaper in the long run to get a "turn key" with owner support (at least for the first race). It may cost a bit more in the short term but the long term pleasure will not be obscured by endless repairs/rebuilds.

Rod

 

[thruthefence]

OT for Rod; Ever use a "split weber" carb set up on the Mini, (or the Twin Cam, for that matter)?

 

[evelrod]

I've never done the split Weber deal, myself. I do have several friends and fellow Mini racers that uses the setup. I use a single 45 DCOE-9 on my Mini and a pair of 45 DCOE 152's on the Locort. I have some 40's and a pair of 44 PHH Solex that I once considered splitting....For me, bad idea. I do vintage racing and cutting up an expensive carb is not in my playbook.

Try Bill at "Mincomp", Dave at "APT", Joe at "Huffaker Engineering" or Mike at "7's"

http://www.7ent.com/categories/fortech-racing-components.html?sort=featured

They all have done the split multiple times. It's also detailed in Vizards's book on the Mini if you have access to one.

Rod

 

[LadaTrouble]

The Triumph 2000 and 2.5 had a primitive PCV valve using a diaphram - they were pretty useless,gummed up and cracked the diaphram. BMC used the same system,and I converted my Austin 1800 to a conventional inline PCV valve...it seemed to work ok,at least much better than the original system.