1700 Super Sprint Compressions

[Temple Cloud]

What should the compressions in psi be for Cross Flow Super Sprints ? Standard cam I think. The to and from if poss. Thx

[Nigel Blandin]

All the same. The actual number may vary, but you are looking for consistency.

[Roger King]

If it's standard spec, around 180psi, but as already stated, consistency is the key because gauges vary so much.

[Temple Cloud]

Thanks for that. Three are fine at 180,170,165 but the number 4 is just 145 with 30% leakage from the inlet valve.

So I think I need the head off and take a look

[Roger King]

Firstly, are you doing the compression test with a warm engine, the throttle held fully open and the ignition disconnected? That is the correct way to do it.

15psi is about the variation you can accept, so yes, four is too low. Before you do anything, take the plugs out and squirt a little engine oil into each cylinder, crank it over and try the test again. If no. 4 has improved significantly, it is more likely to be rings than valves. Ideally you should also use a leakage tester which will not only give you a reading, but you will also be able to hear if the leakage is coming out of the crankcase breather, the inlet manifold, or the exhaust, thus identifying the source of the leak for certain.

[Temple Cloud]

Thanks. It's certainly leaking from the inlet valve and we were using a leakage tester. I did this with someone who supposedly knows what he's doing but I just wanted to get someone like you who also knows what they're doing to give me a second opinion about what needs to be done and how urgent it is. The guy who did the test and who was in a garage obviously has a vested interest in getting work for himself lol

[East Kent AR]

Temple Cloud  I suspect you are not aware that Roger King is the Cross Flow Guru. He's probably built more Kent engines for 7's  than most. His advice is very sound.

Piers

[Temple Cloud]

Sure, I appreciate that and exactly why I posted the thread in the hope that someone like Roger could give me the benefit of their advice

[Temple Cloud]

Well, the good news is that as the car is still under warranty, the dealership I bought it from have agreed to take it back and do the necessary work to resolve my issue. Better that than risk dropping a valve into the cylinder....

[OldAndrewE]

Do you (or anyone else) know if the Super Sprint had anything done to the exhaust valve seats, i.e. hardened seat inserts for unleaded?  This may be the time to get that done

[Temple Cloud]

Thanks very much for the suggestion and I'll make sure that idea is implemented if it hasn't already been. This forum is just so valuable for a Caterham noob like me. Brilliant.

[Roger King]

From Caterham, no they didn't have hardened seats.

[Temple Cloud]

Thanks for that. And would that be a good idea to do at the same time as sorting the leaking inlet valve ? And if so what do you think would be the cost implication, over and above the leaky inlet valve ? Thanks for any info....

[Roger King]

If you have the head off it would be madness not to fit unleaded exhaust seats at the same time. I can't give you a price since I stopped building engine twenty years ago, but it shouldn't be a huge expense. Just make sure the job is done by someone who knows what they are doing.

[Temple Cloud]

Thanks for the advice Roger. Most useful...