7 hp EXCESSIVE CRANKCASE PRESSURE

kemp1942 · Post by **kemp1942** » Sat May 22, 2010 2:26 pm

Arabella is suddenly sick !. During her 1st outing yesterday (apart from the MOT run) she began smoking badly and suffered a loss of 'pulling-power'.

The smoke/fume is from the crancase breather valve pipe.

This is the recon engine ex Gary Rooke which of course is not yet run in - I have checked compression and am getting about 60psi from one cyl. and about 75psi from the other.
Is excessive c'case pressure a sign of rings gone ? or is there likely to be another cause ?? The breather valve is new.

Any advice appreciated - although I suspect I have run out of time to fix her before the rally ?

kemp1942 · Post by **kemp1942** » Sat May 22, 2010 4:00 pm

Have now discussed with IP who agrees most likely cause is broken rings though the compression being achieved puzzles him slightly.

Am going to reduce the oil level - it's currently at max - might reduce the fumes/might not !, so it looks as if Arabella is out of the Concours since a requirement is that she is driven to the site - 7 miles of heavy smoke and a potential seize-up is a non-starter methinks.

k. rogers · Post by **k. rogers** » Sat May 22, 2010 9:34 pm

Ian, you are still bringing Arabella aren't you? There will be alot of disappointed members (not least of all, me!) if she isn't there and there is an excellent chance you will resolve the problem with the expertise there will be available at the rally! Just out of interest, what oil pressure reading are you getting?

kemp1942 · Post by **kemp1942** » Sat May 22, 2010 9:41 pm

Hi Ken.

Yes still trailering her to the rally.

Peter Atkinson and his good lady are coming along on Sunday to be reunited with her - just a shame they won't be able to have a run in her.

I have 20 to 25 oil pressure which I have had since I installed the engine.

Ian

k. rogers · Post by **k. rogers** » Sat May 22, 2010 9:49 pm

That sounds ideal, so it isn't to do with excessive pressure. I'm clutching at straws here with my own limited knowledge, but sometimes I find any suggestions can lead you to the problem, sometimes indirectly: you mention the new breather valve, I know it sounds a bit obvious but is it positioned correctly as per the manual and is the drain hole clear?

kemp1942 · Post by **kemp1942** » Sat May 22, 2010 9:57 pm

Yes - it's a new one I fitted. With the cover off I can see the c'case pressure forcing a couple of the vanes open against the pressure of the star. The drain hole is clear

k. rogers · Post by **k. rogers** » Sat May 22, 2010 10:05 pm

Provided the vanes of the diaphragm are directly over the holes in the valve and the 'prongs' of the star shaped plate are over the vanes, then it can't be that! The annoying thing is that I am sure I have read somewhere, may have been on this forum, of a case where someone was experiencing a similar problem - over to the rest of you to see what else can be looked at!

k. rogers · Post by **k. rogers** » Sat May 22, 2010 10:27 pm

Ian, thinking of your sudden lack of power and the difference in compression between cylinders, it may be worth checking to see if any of the valve springs are broken or if one of the tappets has worked itself tight, although I can't see how this would effect crankcase pressure - just trying to eliminate other things before going down the cylinder removal route!

Keith Andrews · Post by **Keith Andrews** » Sat May 22, 2010 10:29 pm

Rings....
Have they beeding in correct?
Was the final hone patterns correct?
When the cylinders where bored where they sized/matched to the individual pistons? If so was the right piston put in the right bore?

60psi from one cyl. and about 75psi from the other.

Thats around 25 to 30% difference between cylinders....Thats a huge difference, espec on a new engine.
To put that in perpective...take sb block chev with around 165 lbs a variation of 5to 7% is acceptable...25% is 120 lbs to 165 lbs...considered to be very worn after well over 200,000 miles

With a 25/30% between 2 cylinders is loading the crank, bearings unevenly way to much....it is this sort of thing that breaks cranks, espec on a 2 cylinder engine.

kemp1942 · Post by **kemp1942** » Sat May 22, 2010 10:45 pm

Hi Keith. This engine was reconditioned back in about 2003 for an ex-member who eventually emigrated. Sold his car but the engine was left in the care of another member and efforts were made to sell it over several years until I bought it 'as seen' as a temporary replacement for this season until my original engine was reconditioned!
So have no idea as to how well or otherwise the recon was done.
I will be refitting my original engine sometome after the rally now rather than later this year - am picking up it's rebored barrells at the rally so it's not the end of the world - just a nuisance that I won't be able to drive it around !

Post by **Forumadmin** » Sun May 23, 2010 9:20 am

To check rings try putting some oil in cylinder before doing compression check. Also check tappet clearance and make sure valves are all going up and down correctly. Could be collet out or push rod bent.

I do not know about your engine but you can get a lot of smoke if the oil return hole from rocker box is blocked or a bent valve has opened up valve guide.

Head off low compression cylinder should tell you in an hour what is wrong.

kemp1942 · Post by **kemp1942** » Sun May 23, 2010 3:18 pm

Having 'oiled' both barrels the psi's are now o/s - 65, n/s - 63 which would seem OK ?

Have spotted another issue, related to the excess compression - the gasket (if there is one) or the sealant has 'blown' near the base of the o/s barrel flange to crankcase. So its's blowing/sucking in rapid succession at that point - see photo.

There is also now evident a trace of a rumble or muffled knock intermittently from the engine, possibly from towards the rear. Have checked the flywheel - it doesn't appear to be loose (noise still there after depressing clutch) so something is amiss internally I think

Have decided to leave all alone for now and take the engine out after the rally. I will have my rebored barrels back for my own, original engine by then so will rebuild it and put it in in place of this 'recon' engine

PAUL BEAUMONT · Post by **PAUL BEAUMONT** » Sun May 23, 2010 3:44 pm

Ian, I reckon that you should have kept quiet, trailered to Wakefield and when you started it .... Oh dear..... you would have had an army there removing the engine fully servicing it etc...
But now, as Ken says I am sure everyone will be grateful that its there even if incapacitated.

See you at the weekend!

kemp1942 · Post by **kemp1942** » Sat Jun 05, 2010 3:50 pm

I have been stripping my 'sick' engine to try to see what was giving me the excessive crankcase pressure and lo & behold - found it ! (You were correct Keith in your 22nd May post re the rings)

See attached pics - main reason was the rings had 'set' in their grooves on the piston underside whilst the engine was standing for some 7 years since the reconditioning and the bore had rusted. Rust still evident below the end of the piston skirt travel. Gasses going straight through into the c'case.

The 'blow/suck' with oil coming out on the 'blow' cycle at the base of the barrel (see May 23rd post and picture) was due to the mod in photo 2, done presumably to re-attach the baffle plate support ?. Only two of the holes had screws in them - the 3rd with no screw in it, and which was not completely covered by the pot base flange, was allowing the c'case to vent.

Next time I buy a 'recon' engine I will want to see it running first !!!!!

My original engine will be going back in next week once I have head gaskets and in the meantime - does anyone have an 8HP standard size piston c/w rings in new or S/H condition ?? (This is the size the recon engine had been bored out to - 3.034")
Or a pair since one on it's own may not match weight-wise ??

PAUL BEAUMONT · Post by **PAUL BEAUMONT** » Mon Jun 07, 2010 12:57 pm

Ian, Think I might have a new Bricovmo piston for 8hp. Will try to remember to check after spares tonight.