Smoking cross flow

[Barry Thompson]

Noticeable smoking exhaust on 28,000 mile supersprint.  Previously always only a puff when starts up and only a little oil burnt   Second run since service  correct oil put in by very good mechanic and mot pass.  It seemed normal trace of smoke only and no problem like now . Does the smoke mean that engine needs to be worked on and any ideas what lies in front of me  before I drive it to my good local garage.  Should I worry driving it. Thanks 

[elie boone]

First you have to define what causes the smoke, maybe it's just a valve stem seal that has come off if there are any to start with. A compression test followed by a leak down test would give you an idea where it might come from or as simple as your oil level is just too high.

[Roger King]

28,000 miles is about the point that a road driven Supersprint typically starts to give up the ghost. You have pistons designed for a 55 bhp engine being used with a much higher than standard compression ratio and producing around 120bhp; not only that, it will be revving much higher than normal.

Assuming that nothing else is found that is wrong, it is usually the piston rings and/or pistons that give up. The rings are much more highly stressed than they were designed to be and lose their tension, failing to seal, and the pistons sometimes crack between the rings. Either way, the engine gets smokey. The only answer if this is the problem is a new set of pistons and rings. If you can stretch to it, a rebore and a set of 83.5mm forged pistons are far preferable, giving longer life and more power.

Before anyone says Supersprints last much longer than that - yes, I have seen a healthy Supersprint with 80,000 miles on the clock, but I have also seen the above failure at less than 2000 miles. 25,000 miles is merely a typical figure and given the average annual mileage that a Caterham does means that the car would have been well out of warranty by that point.

[HendrixsWhiteStratReturns]

Barry - Roger is spot on (what he doesn't know about Xflows isn't worth knowing). Mine's on 23K and smokes but has been like it since 18k miles - soon she'll be off the road for engine refresh but regular oil changes (with the right Valvoline VR-1) and not pushing the car hard has been fine for me...

[Barry Thompson]

Thank you for your replies which informs me.   Printing out to give to my local mechanic who owns a specialist Audi VW garage but was trained in such cars as the 7 and classics and enjoys something different     On the phone he agreed with your suggestions.