x-flow harshness

[lowlander]

My 1600cc x-flow sounds harsh above 5500 rpm. I originally thought this was valve bounce but I've fitted stronger valves and it still sounds harsh. The engine is standard and runs on twin 40's (aaprox. 100 bhp). The engine pulls well and certainly wants to rev to 6000+rpm.

 

Any suggestions?

[Simos]

Oh, they all do that Sir!

[James Arnold]

I find wearing ear-plugs cures a variety of strange noises not only from the engine, but also the passenger.

J

[cskip]

I thought it was value bounce as well. I still haven't got to the bottom of the problem. Mine sounds bloody dreadful above approx 5250 RPM. Like the whole engine is going to implode. I never take mine above 5250RPm as the engine will not rev any higher.

 

Going to have it tuned later this week. Hopefully this will help.

 

I will be interested to here anybody's comments on this.

 

Clive.

 

Crossflow - Loud and Proud!

 

[lowlander]

Clive

 

The engine in my car certainly wants to rev higher. It will quite happily go to 6000+ but as you say it sounds really harsh above 5400 - 5500 rpm and as I have a certain degree of mechanical sympathy I don't tend to rev it that hard. Would be interested to hear of other peoples experience of standard crossflows.

 

Martin.

 

[lowlander]

Clive,

 

Does the engine rev freely to 5250 rpm and then refuse to rev any higher or is it a case of the engine getting sluggish above say 4500rpm? Does the engine run O.K. at lower revs? (i.e. smooth with good throttle response). I'm assuming that you've checked things like the ignition timing, points (if you have them), plugs, leads, etc. Sounds a strange one to me. Is your x-flow standard or is it had a bit of tuning work done?

 

Martin.

 

[Violet Elizabeth]

My crossflow will rev quite happily to 6000 and beyond indeed a friend took it up to 7000, 'cos he thought the redline was where the dial finished. It starts sounding like a bag of bolts above 6000.

[Super_Rich_Bernie]

On tuned BMC A series engines a different contact breaker set was available to stop the points bouncing at higher rpm. This just had a stronger spring to stop the heel of the contact breaker bouncing off the lobe of the distributor shaft.

 

It could be that some CB sets for X-flows are not as good as others and the ignition is breaking down at high revs.

 

I'm no X-flow expert, but it sounds feasible and would cost less than a fiver to fix!

 

Jonathan

[Roger King]

Martin,

 

If you have one of the so-called 'unleaded' distributors (post 1989 vehicles, unless you've changed it), you will be running around 10 degrees retarded at higher revs compared to what the engine wants. This is a feature of the appalling advance curve in that distributor.

 

This leads to the engine running inefficiently at higher revs and can have the effect described. In some cases the advance is even worse.It can even change while the engine is running if you are using the Caterham supplied system that Lucas originally made as a cheap electronic conversion for things like the Morris Ital.

 

The answer is to change the distributor and ignition system - but I am only guessing that this is your problem.

[Old Septimus]

I had my standard GT spec 1600 balanced statically and dynamically 15 years or so ago, flywheel, clutch the whole lot and the difference was striking. It will rev smoothly to 6500 without sounding rough although the power drops off at 5500. Sometimes you need to over-rev to avoid an upchange on twisty circuits - eg Croix. When put on the rollers it produced 82 at the wheels. Old, slow and fun.

[cskip]

Martin,

 

The engine Revs up to 5250 very freely and will keep going up to 6000rpm, but is very sluggish from 5250-6000 and sounds very harsh.

 

It is a completely standard 1600 sprint.

 

I'm not technically minded, but very willing to learn!. So I have booked a Tuning session at a local Rolling Road.

 

Roger, what recommendations do you have for a replacement ignition system?

 

 

Clive.

 

Crossflow - Loud and Proud!

 

[lowlander]

Roger,

 

My distributor is electronic (aldon) with a lucas side exit cap. It has a mechanical advance. On the basis that the it is electronic it can't be points bounce. Could the advance curve be that much out at higher revs with a mechanical advance?

 

Cheers.

 

Martin.

 

[Roger King]

Yes, it can be miles out, because that is how the unleaded dizzy is specified, i.e. there is nothing wrong with it, it simply doesn't suit the engine. If the ignition if of the Lucas type as supplied by Caterham you can get extra massive errors when the rotor arm works loose (bizarrely, the rotor arm controls the timing).

 

With regard to replacement, 3d mapped is best, but there is also the Lucas constant energy system (not related in any way to the above system) which is very reliable and gives a monster spark. The advance curve needs a small tweak to suit a Crossflow, but we do this before they go out of the door - as I assume, do other suppliers.

 

We have always told customers that we will refund if they can't tell the difference and so far no-one has ever asked.

 

Edited by - roger king on 16 Apr 2002 15:11:25