Xflow Compression Query

[M1ke]

HI, I'm a newbie 7er and I wondered if you could help.

 

I recently bought an '87 1700 Xflow with 17500 miles, which at the time of buying, was running well with no smoke (see where this is going?). After a few weeks of blatting I've started to notice more and more smoke from the engine, especially when pushing hard at higher speeds 60+. The car hasn't been reved excessively, I'm still changing shortly after 5K when really going for it. Although the car is happy to rev much higher.

 

I was aware of this weakness when buying the 7 but couldn't see any signs of trouble (no compression readings taken). Taking them now I get (Front to back) 180, 150, 132, 145.

 

Q1 Are these Ok, bad or really bad?

Q2 What are the most likely causes? Wore piston rings I assume, others?

Q3 Does the large variance indicate anything?

Q4 What's it gonna cost?

Q5 Anything I can do to reduce the problem?

 

 

Thanks all and happy blatting

 

Mike S

Ps. Thanks L7CGB for the excellent blatchat.com

[Graham Sewell]

It certainly looks a little strange. The readings should be within 10% so if 180 is highest, the lowest should be greater than 162.

 

Firstly, checking technique, the engine should be warm and all spark plugs removed. If you are using the Gunson gauge then I have found that this can sometimes unscrew itself between screwing it in and getting back to the starter key. It is worth double checking.

 

If you still have low values, put a tablespoon of engine oild down the bore about to be tested. If things improve then you have a problem with piston rings - otherwise it could be head gasket or valve seats.

 

Quick check for head gasket would be that either your oil will discolour with the air being forced through it , or you will lose coolant big time. If you have the time, and it is not the piston rings, then a head overhaul should help. New gaskets and re-lap the valves. That should make the top end air-tight and restore the compression. If you are lucky and it is head work, then it is a day of your time and a few tools - otherwise it is time to upgrade and talk to Roger King as it will not be much cheaper to remain standard as the labour cost is the same.

 

Good luck.

 

Graham

 

Low tech luddite - xflow and proud!

[M1ke]

Engine was warm(ish, idle for 5-10mins,but it's not too warm today) and I only had one plug out at a time. Will re-check tomorrow with all plugs out.

 

When you say a table spoon of oil down the bore, am I right in assuming you mean down the plug hole?

 

Thanks for the advice so far

 

Mike S

[Roger King]

Yes, Graham will mean down the plug holes.

 

All plugs should be out and you should be on FULL THROTTLE, otherwise the air can't get into the cylinder to give a compression reading.

 

Typically, a Supersprint should show 180psi - 210psi, but gauges vary tremendously in their accuracy. The most important thing is to have the figures within around 10% (again, as Graham says).

 

Afraid this is common with Supersprints at this mileage and the usual cure is to fit forged pistons.

[YW Sin]

Roger king,

Thanks for your usual technical info which I am sure many readers such as myself very much appreciate.

 

As an X-flow owner, I wonder what is the typical life span of a standard X-flow (Caterham) Engine? 17000 miles just seems waaay to low.

 

A ll standard, Classic 1.7 X-flow

[Roger King]

The best I have seen from a 1700 Supersprint is 60,000 miles and the worst was 2000 miles. Both were used on the road not the track and both failed for the same reason (broken piston). Typically 15,000 - 20,000 miles is about what you will see with road use (awaiting protests from much higher mileage owners now) and the most common failure is the piston rings.

 

Basically, the Supersprint is an excellent spec, but the pistons and rings are actually from a 1300ccm 55bhp engine and aren't designed to take what is thrown at them. If the pistons are changed for forgings and a few other details are dealt with you can extend the life by tens of thousands of miles as well as seeing a power increase.

 

The 1600ccm engine is pretty much in standard trim and tends to last much longer. In other words, it isn't that Crossflows are inherently short lived, just that the choice of components has to suit the application.

[Roger King]

The best I have seen from a 1700 Supersprint is 60,000 miles and the worst was 2000 miles. Both were used on the road not the track and both failed for the same reason (broken piston). Typically 15,000 - 20,000 miles is about what you will see with road use (awaiting protests from much higher mileage owners now) and the most common failure is the piston rings.

 

Basically, the Supersprint is an excellent spec, but the pistons and rings are actually from a 1300ccm 55bhp engine and aren't designed to take what is thrown at them. If the pistons are changed for forgings and a few other details are dealt with you can extend the life by tens of thousands of miles as well as seeing a power increase.

 

The 1600ccm engine is pretty much in standard trim and tends to last much longer. In other words, it isn't that Crossflows are inherently short lived, just that the choice of components has to suit the application.

[YW Sin]

Thanks Roger, I will watch out for that blue smoke 😬

[M1ke]

Ok, results now in for my poorly xflow....

 

200, 163, 165, 170. Which are much better than before but still way out of the 10% limit. Adding a little oil to the sparkplug bores gives 240, 195, 190, 200. So, it looks like the pistons are worn.

 

Major re-build time?

 

Thanks for all the help so far, it really is appreciated and I hope I can rturn the favour some day.

 

M1ke S

 

[YW Sin]

Mike, if your car is smoking with blueish colour, it most probably means worn piston rings. If the smoke colour is black, you just need to retune the carburettors.

 

 

 

A ll standard, Classic 1.7 X-flow