Sigh, the valve seat in #3 is cracked. If you put in another exhaust valve, it will burn through again. The block and head , in the 948, both have design flaws, with too little iron reenforcing the exhaust seat an #3 cylinder, causing the seat to crack, and the cylinder to warp. The first can be fixed by cutting out the exhaust seat and installing an alloy seat. The second was somewhat fixed by installing a special piston that was made with an extra oil scraper ring at the bottom of the skirt. They are likely impossible to find today. Possibly resleeving it with a steel liner might work.
I haven't inspected the valve seat yet, but I think that head has hardened seats (there's an invoice in the paperwork). It's a 1098. It's happy enough with the spare head until I get the chance to deal with thus.
Old fashion advice,1 egg cup of petrol Redx down each spark plug hole leave over night.then make sure your your plugs are clean don’t put them in turn the engine over for a few minutes then put plugs in start up this will make a lot of white smoke loads of smoke rev up until clear and then a good run old fashion decarbonise, but it is only my opinion I use to do this on my old BMC engines from the 1950s and oil and filter change . Also the rule of 9 for the valves adjustment,and a egg cup of redx in the petrol tank will be a good idea now and then.
Your engine steady bar is on the wrong way round. It sits better the correct way.
This was a very common fault on the A series engine, and I’ve replaced several over the years, and usually no.3 cylinder!
I was speaking to someone earlier who experienced the same. It'll go to a proper machine shop.as probs needs new valve seats.
Sigh, the valve seat in #3 is cracked. If you put in another exhaust valve, it will burn through again. The block and head , in the 948, both have design flaws, with too little iron reenforcing the exhaust seat an #3 cylinder, causing the seat to crack, and the cylinder to warp. The first can be fixed by cutting out the exhaust seat and installing an alloy seat. The second was somewhat fixed by installing a special piston that was made with an extra oil scraper ring at the bottom of the skirt. They are likely impossible to find today. Possibly resleeving it with a steel liner might work.
I haven't inspected the valve seat yet, but I think that head has hardened seats (there's an invoice in the paperwork). It's a 1098. It's happy enough with the spare head until I get the chance to deal with thus.
Old fashion advice,1 egg cup of petrol Redx down each spark plug hole leave over night.then make sure your your plugs are clean don’t put them in turn the engine over for a few minutes then put plugs in start up this will make a lot of white smoke loads of smoke rev up until clear and then a good run old fashion decarbonise, but it is only my opinion I use to do this on my old BMC engines from the 1950s and oil and filter change .
Also the rule of 9 for the valves adjustment,and a egg cup of redx in the petrol tank will be a good idea now and then.
Misfires always worry people if it's not electrical
Surprising it was making any compression at all with that valve. Looked like it had been nibbled on!
It was! I'm surprised i drove best part of 500 miles with it!
Lovely, ...
Good luck. Don't you have a suicide switch on the starter relay ?
No suicide switch.
Did you ever find the missing valve bit?
Don't think I did tbh!
Nice one 👍👍
Thanks
This is me just finding out you have a TH-cam channel 🥲
I'm crap at publicising it on insta!