Blowby advice

[Violet Elizabeth]

My xflow is smoking rather a lot from the oil breather. I have been reliably informed that the piston rings are getting worn (engine has done 14,000 miles) and a rebuild (or swap) is on the cards. If I leave it for another 6 months or so what are the possible outcomes ? Will it just get smokier, or is something terminal going to happen as the wear increases ? I don't actually mind the fumes, its the chance of something doing further damage that worries me. Advice gratefully received.

[AMMO]

My Supersprint also smokes from the breather. It has done 16,000 miles. I've got a catch tank but nothing seems to collect in the bottom of it. Even at tickover smoke comes through the louvres of the bonnet. I think the correct technical term for this is "knackered". I have started telephoning around today for a Zetec as driving it like this is just no fun. The idea was to poodle around this Summer and convert it next winter. Can't wait another year to start enjoying myself.

 

AMMO

[Drumster]

My x/flow started smoking around 18,000 mls and finally had it upgraded by Roger King at approx. 21,000 mls. If you wany any real advice then Roger is your man. My only advice would be stick with the x/flow and a rebuild rather than a swap.

 

Chris Alston

[Roger King]

From Roger to Noger,

 

What you have is absolutely typical of a Supersprint and at exactly the right mileage. Whoever told you it is ring blow-by is spot on.

 

As to what will happen. Possibly nothing except a worsening of the situation, but it is not unknown for Supersprint pistons to break - usually not catastrophically.

 

The only long term solution is to fit forged pistons, but they have the added bonus of around an extra 8bhp thanks to lower friction and weight.

[AMMO]

Maybe I'm a bit too hasty to slag off the old Crossflow. My engine building mates tell me that it is a good engine if put together properly. I've never driven a car with a sorted Crossflow so maybe I shouldn't be commenting on this. Maybe Caterham have just stuck nasty cheapo pistons in and they wear out really quickly. I think the mileages we are talking about here are really pathetic. I bought my car with the specific intention of converting it to Zetec. I think this engine will give me the sort of performance and longevity I want, so I suppose I'm biased. However, pricing up all the bits I need to do the Zetec conversion comes to a lot of money. So maybe freshen up the Crossflow and do the Zetec later. How much for a set of pistons Roger?

 

AMMO

[Violet Elizabeth]

Thanks for the advice Roger. Piston failure (whether catastrophic or not !) doesn't sound like something I want to get involved in, so will investigate the possibilities. Cheers.

[PeterS]

AMMO

My crossflow engine had a precautionary rebuild by Roger King at 45000 miles. It had done a number of track days, and many runs up Prescott Hill, as well as trips to France, Switzerland, Germany, Holland.

When I sold it at 67000 miles (from memory) last year, the engine was still working beautifully.

So I don't think that the basic design was all that flawed.

[Tim Seipel]

Really does depend on how the car is driven. If thrashed alot but more importantly at high revs then more wear.

 

If you mind the fumes............buy a K series car!

[AMMO]

PeterS, was your engine a 1600 or 1700? I'm sure yours was very nice after Roger King re-built it for you. The trips and excursions you describe are exactly what I would like to do too. I've also had an email today from someone who has done 20K in a 1600 with no problems. It seems to me that the 1700 cc Crossflow as supplied by Caterham is a bit of a dog. If you bought a Ford Focus (or Ford Escort when it was new)and it needed an engine re-build after 16.000 miles I'm sure you would be pretty pissed off. Say the 1700 cc makes about 125 bhp when not breathing heavily, that's less than 75 bhp per litre. Should go 60.000 miles between re-builds, full stop. Even on cast pistons. If it doesn't the parts are crap. There are three people on this page saying their engines are blowing oil and Roger King saying that this is normal for this engine. No point defending it then really. For the same money it would cost to re-build the Crossflow properly you could put the money towards a Zetec which would be more powerful with more civilized engine characteristics. I like old engines that produce lots of horsepower reliably. They are good fun. Especially when you see off modern machinery. But old engines that produce little horsepower unreliably (as in my case) are no fun at all.

 

AMMO

[Graham Perry]

Ammo, I think forged pistons are about £ 450 a set

[Graham Sewell]

My 1700 xflow has no crankcase ventilation and hence has emitted a small quantity of rust prevention oil throughthe filler cap from the day it was bought (20,000 miles ago) and this has not got any worse. Depending on the day, it has been measured between 126bhp and 132 bhp which is about right for an 8 valve engine that peaks out at 6000 rpm.

 

I will be doing compression tests and other checks in a couple of weeks to see what state the engine is in this year. Note that my car will never go near a track in anger and hence use of WOT is limited by the boys in blue.

 

Cheers,

 

Graham

[Petrolhead]

When I built my Xflow for a Westie I used the Twin Cam Flat Pistons with the height reduced to allow a 11:1 compression ratio. I married this up with a Kent 244 cam, Aldon Dizzy, 2 x 40's, lightened and ballanced. The engine went like a train and was very reliable giveing 20 - 25 MPG depending on right foot.

 

This was a while ago, Roger what do think about using Twink pistons are they still available and an alternative from a cost point of view?

[Roger King]

The Supersprint engine uses pistons from a 1300ccm Mk2 escort. It is therefore not surprising that they give up fairly early in life because they were designed for an engine producing around 55bhp. The breathing problem is not indicative of a poor piston design, but stems from the application.

 

It has nothing whatever to do with the engine being a Crossflow either. If a more suitable piston is used, the problem simply doesn't happen.

 

The Twincam piston is much more robust, but there are theoretical problems with running a flat piston with a flat head. There is effectively no combustion chamber and therefore no squish. On top of this you have a rather long flame path. Both of these can lead to combustion problems.

 

I am well aware that several people have built engines like this successfully, but we find better results when there is a proper combustion chamber.

[Petrolhead]

So which pistons do U recommend Roger?

[Roger King]

Best pistons to use are forgings. If of suitable design and using modern ring technology you will lose lots of weight and friction, but gain strength and longevity.

 

The friction difference is surprisingly large and you can gain up to 10bhp through this alone! Of course this comes at no expense to driveability (quite the opposite). Common sense might suggest that lower friction would indicate poorer ring sealing, but again the opposite is the case.

 

Not sure as a commercial operator that I should be recommending specific products in this forum. It could be construed as taking advantage for the simple reason that we sell some of them.