valve chest breather/diagnosis of contributing issues

[Graham Barker]

I would like to see the photo of your breather. Does this men that you do not have breather holes on your tappet cover?

[circeonya@hotmail.com]

The fiter is hollow fine gauze.  The breather holes in the valve chest cover have been closed.   The other interesting mod on this car is the radiator overflow bottle.  Radiator cap is airtight and a pipe runs from the outlet of the overflow pipe to the bottom of a bottle in the firewall box.  Overflow water is sucked back into the radiator as it cools.  I suppose some pressuisisation occurs ?

[Bob Culver]

I ran my car with a pipe into the air cleaner, not because fumes were a problem but to try and reduce condensation and short main bearing life. I am not sure that drawing the oil mist from the valves is a good idea. A tube to below is possibly prefereble if you do not get whiffs.
For decades my Minx with a down tube suffered heavy blow by due wide top ring gaps and later broken rings to the extent that followers occasionally stopped me to comment on the "steam" issuing below. Performane and economy and oil consumption were all OK. Eventually remedied, idling and slow running and engine idle noise much improved but other factors barely changed.

[JonE]

Ok, well - an update. Have changed the title to better signpost others.
All running well, breather breathing. Did 3 or 4 miles and thought I had some smoke out the back when up above 30mph on a long straight.
Plume of mist from pinhole in oil filler, and when I took the cap off, the mist (exhaust?) came out for minutes.
Plugs are trying to be brown, but took off head after checking compression:
75 85 80 80
Observations:
oil on piston tops as per photo
pistons +40 but not all matched and one is not facing to the 'front'.
Pistons don't feel unduly wobbly in bores at top or midpoint.
Bores clean generally.

Clearly I can see that I need to disassemble further now, but how far?! Do I have to determine the type of pistons now before replacing rings, or should I be safe and take to +050 and new pistons just to prevent future faff when new rings don't correct things?

       

[Robert Leigh]

'Front' marks are put on split skirt pistons to ensure that maximum side thrust on the power stroke is onto the plain side of the skirt, so the split should always be on the valve side of the pistons. I failed to notice once during a quick kitchen table rebuild,which was discovered after Jim Holyoake owned the car. Sorry again, Jim!

[AustinWood]

No problem Robert. That engine always ran very well with late Ruby head and SU carb. Managed to average 60mph from Perth to Dundee in 1966. I thought I'd kept that carb but somewhere along the line it disappeared. Maybe it's still on UR 7179.
Always a smell of oil. Used Castrol XL then because it had a very pleasant smell.

[JonE]

An update on this.
I wanted to repair things rather than contemplate a full rebuild. I've realised that the time involved for such far outweighs that from the sourcing of matched new parts, but also teaches you things along the way, and many peoples' assistance has got me to a position where I feel that this has almost been a successful first rebuild where I've learnt a lot about tolerances. It may be that I'm posting this too early in the 'running in' process, but my gut feel is that something needs tweaking rather than just bedding in needing to take place.

I've replaced the duff piston, and balanced the conrod assemblies to within 2g each (just the entire units, not balancing each end) and reconnected everything on the crank with some Philidas nuts after slightly scraping/sanding the shells in to allow the getting-rid-of paper shimming, the cause of one journal being loose prior to dismantling. I changed the head to a LC one, replaced the valve guides and reamed them with a new reamer. Cleaned the valves up, checked the seats and reassembled everything, discarding the worst of the rings but accepting a far wider tolerance than 6 thou - some in the second row are more like 20. (The discards included gaps of 1", 1/2" and a couple of 40 thou or so!)
The engine runs well and starts fine, but is only 10 miles into being re-assembled. It does presently breathe worse than before, through front piece, pinhole in filler cap, and the added breather pipe.
After 10 miles, did a compression test with throttle open but when engine was cold - 75/105/105/100. (Low Compression head)
This suggests to me that the tolerances on the pistons rings are fine as my treatment of no 1 piston was likely the same as the others. (I just inserted the pistons in as well as I could with fingertips from below, going with the strategy of letting them space themselves)
I'm planning on
1. checking tappets on 1 and 2, and if no issues there...
2. lifting head to check valve seat on exhaust port 1
...before contemplating taking piston 1 out.
Are there any other observations I should add and check, please? I'm presuming that with the valve guides done, at least that removes them from blame and concentrates things elsewhere. Valve seat 1 had the most attention, and I did use some coarse grinding paste to get to 'no daylight' viewable through from the underside.

[circeonya@hotmail.com]

I doubt my engine has had any seious work done on it for a long time and does not have heaps of compression. At some point in it's history the valve chest cover holes have been closed and a pipe with a gauze filter runs from the oil filler tube to a point near the brake cross shaft. Seems to work OK

[Robert Leigh]

I believe UR7179 is now a Chummy which was in Northamptonshire last time I was aware of it. A pity to have changed in my view, but it was probably cheaper than rebuilding the fabric body.

[Bob Culver]

Curiously, whilst a burned valve severely reduces Sevens, moderate ring gaps seem to have less effect. Older manuals allow quite large gaps for refitting, and ring manufacturers allow large tolerance even when new. Pre gapped rings often result in generous clearance, esp after run in.
For 40 years I ran my 1964 minx with poor comp on the handle and genrous blowby. The cars were fitted with large top gaps originally and the 2nd rings were externally stepped, provideing a large flow path. When eventually fixed idle was much improved but little other difference.