Confirming a burned out valve

[sudburypaul]

Hi Folks.

My first foray on this site as a new member (well renewed after a few years). My 17 yr old daughter and I are joint owners of a 1956 Series 2 with 803cc engine. The head is not unleaded converted. We are suddenly short of power with a rattle coming from the top of the engine. The tappets were reset less than a 1000 miles ago, so although I haven't yet checked I suspect they are not the cause of the problem. The engine has just under 41000 miles on the clock - which is genuine.

How would I confirm that it is a burnt valve or diagnose any other problem it may be.

If it is the valve I will convert it to an unleaded head at the same time. Anyone know of good deals/service for this?

Best regards, SudburyPaul

[PSL184]

Do a compression test first. This will determine if it is a valve or a head gasket failure. Also take the rocker cover off and turn the engine over by hand watching the rockers carefully for any strange activity....

[sudburypaul]

Cheers for that - just need reminding to be methodical and work slowly through it all rather than attack it in blind panic!

[bmcecosse]

Don't bother about 'unleaded' !! You really don't need it for normal motoring. In any case - so called 'unleaded' Mini 998 cylinder heads are plentiful - and very cheap. Just fix the problem - but a 'rattle' is unlikely to be a burned valve. As suggested - it's likely to be blown gasket - assuming the engine hasn't lost it's oil pressure ?

[sudburypaul]

Thanks for this.

I'll compression test it in the morning and if that proves ok will take off the rocker cover for a look and listen. There's no indication of a loss in oil pressure but it is going through oil a little bit though not excessively. Depending what the test says I might check for worn piston rings too. Strange, the engine was running fine and then the change almost immediate - a noticeable rattle and loss of power. Hopefully it is just a tappet that's worked loose. The car was off the road for nearly 30 yrs before I re-commisioned it back end of last year. It's bound to have a few niggles. It's a bit like owning a slightly more weatherproof Royal Enfield Bullet.

[phurn]

Sudden loss of power, and the fact it was off the road so long means I'm voting head gasket too. Sounds like a screw in a can of beans when it goes

[sudburypaul]

Hi all and thanks for the heads up on what the problem might be. Turns out that on taking off the rocker cover what looked at first like a sticking valve turned out to be a broken valve spring. On manual crankover the rocker got vaguely near the valve but they soon parted company...
So it is a head off job and replacement gasket anyway. It also gives me chance to examine the valve and replace if necessary. The valve is quite loose so I'm optimistic that the piston is ok.

I've pretty much decided that I won't be converting it to unleaded but will set the valves to the spec advised elswhere on the site. It sounds a good (and cheaper) solution. Loads of useful info on here!

Thanks again

[bmcecosse]

Broken valve spring! Blimey. Usually only happens with high revving engines. I suggest you renew all 8. And yes - set the exhaust gaps to 15 thou and check/reset every 3000 miles.

[mike.perry]

I have had a bent push rod and a stripped tappet lock nut (on different cars) which caused similar problems

[sudburypaul]

Broken valve spring - yeah old Edwina is a racy beast! ll I can put it down to is general fatigue - she is 55 after all and not had any real maintenance for 30 yrs until she came to me. It does give me the chance to do a top-end look-over though, including pushrods etc. First impressions are good though - and it gives my daughter a chance to see how an engine works and do some spannering.

[bmcecosse]

Pushrods last 'for ever' - don't worry about them! Here's a head - it's a bit odd, but would do the trick.
http://cgi.ebay.co.uk/Modified-mini-cyl ... 3cb6c26cf0
Or this one.... http://cgi.ebay.co.uk/Classic-Mini-Cyli ... 3a65010d08

[dalebrignall]

i had a tappett adjusting screw shear last year i found the remains under the rocker shaft,that was very lucky .

[MarkyB]

"A bit odd" seems like an understatement, different length valves and rather large exhaust valves.
A picture down the port would be interesting.
I wonder if it was made for economy, or a particular cam?

[bmcecosse]

I suspect it has been fitted with the larger exhaust valves from a 1275 head - which are longer. It's not be ANY means a 'performance' head - someone has been very free with the 'types' making it appear to be something it very definitely is NOT!

[MarkyB]

Any idea why this might have been done?

[bmcecosse]

Ooops! When I look at it properly - it's the inlet valves that are longer - so I guess larger/longer inlets have been fitted - from a 1275 head. I suppose it may just have some performance improvement - but the chamber shapes are not clever.......

[sudburypaul]

Pushrods last forever - excellent. Last engine I rebuilt was a high compression BSA 250 Barracuda C25: High Profiled cams and a ratio of 10.1 pushed the original C15 engine to its limits. Everything would bend, con rod, crank, pushrods... Nice not to worry about everything being bent out of shape!

[bmcecosse]

The pushrods won't bend unless something makes mechanical contact....... ie valve meets piston.....