6 replies to this topic

[1984mini25]

Standard 998, 66k
Basically the mini has recently started puffing out clouds of blue smoke on start up, and running rough untill it clears from cold. It doesn't seam to do it every time, but seams to be worse if its cold or damp.
Other than the occasional running on when switched off (might be related to the oil burning?), theres no other running problems or loss of performance.
Would I be right in thinking the valve seals have gone? As unfortunately being my only mode of transport for work, I'm having to keep a close eye on the oil level.

[bmcecosse]

Could be all manner of things.....start by checking and resetting the valve gaps. A compression check would be a really good idea too..........

[1984mini25]

Well it only smokes for the first few minuets of running and once it's cleared, it runs perfectly fine. Also it's not running hot or losing any coolant and the breather connected to the carb isn't blocked either.

Edited by 1984mini25, 07 July 2012 - 11:46 PM.

[bmcecosse]

Oil running down the valve guides............

[BVY]

I think the run on is caused by a build up of carbon on the face of the pistons and valves etc. Because it's so hot it can ignite the fuel. Mine stopped running on after using some fuel system cleaner in the fuel for a couple of tanks...

[Stevie W]

I'd go with Roy on this one.
Initial smoke on start-up from cold indicates oil sitting in the cylinder head channels around the valves, is running down the valve guides overnight and being burnt off on first start up.
This could be simply be due to worn valve guide seals and/or worn valve guides themselves.
Steve.

[1984mini25]

Well i've since whipped the head off earlier today. The head and piston tops were a bit coked up, but by no means the worst i've seen and it cleaned off pretty easily. Hopefully tomorrow i'll be able to strip the head down, clean it and the valves, lap them and change the seals. Then once it's all back together, hope it doesn't smoke. The only other thing I noticed now the heads off and theres a clear view down the back of the engine, is the exhaust bracket on the diff has sheared clean in two.