Rebuilt engine,compression 200,but running on.

[eddietiv1]

Right`engine just rebuilt,compression 200 which they think is too high,but on the running in stage it was pinking and running on when turning ignition off,just taken it to aldon in the west midlands.Stripped the distributor and sorted what needed sorting,theyve cured the pinking but its still running on,all they can suggest is that it may be running a peakier cam of which im not sure,hence why its still running on.What do you think and where do i go from here,i feel as though im getting knowhere,the engineer as told me to carry on running it in when hes cured the oil leak and take it from there,please help.

Edited September 7, 2012 by eddietiv1

[Guest Mick RichardsChange...]

Sorry Eddie, give us a clue I don't know what vehicle you're talking about is it a Honda CRV ?

 

Model/Engine/Modifications/Plugs/Carbs-Injection/Inlet Manifold/Exhaust Manifold/Petrol used (gasp) will do for a start. Tedious I know especially if your car and engine is well known to most others.

 

Mick Richards

[eddietiv1]

Sorry Mick,tr6 1971,twin su`s,bp6es plugs(aldon said should be bpr6es with electronic ignition)richer carb needles,jet conversion,150 bhpcam part no 307689,full engine rebuild crank up etc etc etc.

[WWT338J]

Has the head been skimmed and are the bores over-size? If so the static compression ratio may be excessive. I had this problem in an engine I bought from Rimmers a few years ago. CR was 11:1.

 

Are you using Shell VMax petrol? That has the highest octane rating of standard pump petrol at the moment.

 

What timing are you using? 11deg BTDC?

 

David

[Guest ntc]

If your readings are right??? you will not run with std fuel and 11 deg

[Peter Cobbold]

If there are over-run valves in the SI butterflies weak springs can allow mixture in when thottle is shut.

Try a grade or two colder plugs.

If air filters are on carbs breathing hot air, fit cold air intake and remote filter.

As others have said spark timing and RON very important for very high CR.

[eddietiv1]

Timing is 12 deg,aldons figures,they did say definitely run on v power,only just found out it was fitted with an hotter cam previously,could that have an impact on it,i will let aldon know this too.Would different spark plugs make a difference,im now going to run the engine in a few hundred miles see how it settles.

[Peter Cobbold]

Timing is 12 deg,aldons figures,they did say definitely run on v power,only just found out it was fitted with an hotter cam previously,could that have an impact on it,i will let aldon know this too.Would different spark plugs make a difference,im now going to run the engine in a few hundred miles see how it settles.

 

Something in the combustion chamber is hot enough to continue igniting the mixture after the sparks have been switched off. It might be a plug. Or it might be a hot exhaust valve. But almost certainly not carbon deposits in a fresh engine. The plugs are easy to check - its process of elimination.

A cam with more overlap than normal will allow the exhaust valve more cooling mixture past it. But cylinder filling and so heat of compression is increased from normal. Add that to the extra heat of compression due to high CR and the envelope is being pushed. So the latter two win out I think- and we have more hot gas to flow out past the exhaust valve. I'd think about a rolling road session to set the spark and mixture* to give max torque in the mid range rpm - if you are getting the most umph at the wheels you have minimised the heat wasted down the exhaust pipe ( ie extracted the most heat as useful work.).

*Have you measured mixture ( AFR) ? - the needles might not be rich enough for the higher CR and cam. A lean mixture burns hotter and you want to keep as much heat out of the combustion chamber as possible.

Peter

[Stag powered]

Long duration cams normally help with running on as cylinder filling is poor at low rpm. Your fundamental problem is carbs. They keep supplying mixture when the ignition is turned off, when injection is switched off fuel is no longer supplied so the engine cannot run on.

I remember Chris Witor the triumph 2000 specialist on about this years ago when I had a PI saloon. It was a common problem for PI engines converted to carbs to run on, even back then. I think he used to recommend an anti run on valve off an Austin Maestro. IIRC, though you might be struggling to find one these days.

The anti run on valve basically lets air into the inlet manifold when the ignition is switched off, weakening the mixture to the point where it cannot ignite

Neil

[Nick Jones]

If the pinking has been cured then running-on, though irritating, isn't really a big problem. It's very common on carb fed 60s and 70s vehicles, made worse by todays petrol.

 

It's caused by auto-ignition and the heat supplied to bring this about mainly comes from the compression pressure, though inlet charge temperature and combustion chamber temperature obviously have an influence. Also the knock point of the fuel is significant. So you relatively high compression is a factor and so is the fuel. You should find that it does it less when running 98 octane.

 

You want the idle speed to be set as low as practical. High idle speed or blipping the throttle before switching off are both likely to cause running on. Back in the days when my Vitesse still had carbs (and it was a champion runner-on!) I used to find that letting it idle for 20 - 30 seconds would reduce the probability, and I also got quite adept at engaging 4th gear, switching off and lifting the clutch just as the engine was winding down to stall it.

 

Other than that you are looking at the anti-run-on valves mentioned above.

 

Cheers

 

Nick

[Peter Cobbold]

If the pinking has been cured then running-on, though irritating, isn't really a big problem. It's very common on carb fed 60s and 70s vehicles, made worse by todays petrol.

 

It's caused by auto-ignition and the heat supplied to bring this about mainly comes from the compression pressure, though inlet charge temperature and combustion chamber temperature obviously have an influence. Also the knock point of the fuel is significant. So you relatively high compression is a factor and so is the fuel. You should find that it does it less when running 98 octane.

 

You want the idle speed to be set as low as practical. High idle speed or blipping the throttle before switching off are both likely to cause running on. Back in the days when my Vitesse still had carbs (and it was a champion runner-on!) I used to find that letting it idle for 20 - 30 seconds would reduce the probability, and I also got quite adept at engaging 4th gear, switching off and lifting the clutch just as the engine was winding down to stall it.

 

Other than that you are looking at the anti-run-on valves mentioned above.

 

Cheers

 

Nick

 

Nick

I think we still need a hotspot to get ignition, eg:

http://en.wikipedia.org/wiki/Dieseling

 

Compression ignition DI petrol engines run at much higher compression ratios eg 16:1:

http://delphi.com/pd...011-01-1386.pdf

( and need 91RON fuel to get it to ignite - so would be much more diffcult with 97RON)

http://lup.lub.lu.se...&fileOId=544314

 

 

I wonder if the TRs are retaining hot exhaust gases to providing the heat, or crankcase fumes providing the fuel?

 

Another thought:

My blown 6 has several litres of hot mixture in the inlet manifold after the butterlfy, runs maybe 60-80C hotter than an atmospheric engine but never runs on using 97RON. But the CR is 8.5. This low compression USA head is so thick that the squish area is not present. On high compression shaved TR heads the squish area will be greater then standard 9.5 heads, possibly providing the localised compression to initiate dieseling and running on.

Peter

Edited September 9, 2012 by Peter Cobbold

[Vitesse Jason]

My old Vitesse 2.5 on SUs would also run in badly, the previous owner had tried a Metro anti-run on valve which worked for a while but eventually failed. I tried various tricks but ended up just flooring the throttle a second after turning it off, this basically flooded it and it didn't run on. The problem was eventually solved by fitting Lucas PI :-)

[Peter Cobbold]

My old Vitesse 2.5 on SUs would also run in badly, the previous owner had tried a Metro anti-run on valve which worked for a while but eventually failed. I tried various tricks but ended up just flooring the throttle a second after turning it off, this basically flooded it and it didn't run on. The problem was eventually solved by fitting Lucas PI :-)

 

So how does flooring the throttle work? I suppose the dashpot oil slows the piston lift to give a rich mixture, and the extra cooling from the extra fuel cools off the combustion chamber?

So there's something for eddietiv1 to try: switch off while pulling the choke, floor the throttle and use thicker oil in the dashpot- can't get richer than that.

[Vitesse Jason]

I suspect that's it, I have to admit I'm not sure why it works but suffice to say that when I wanted to save my embarrassment of the car running on, it worked :-)

[eddietiv1]

Ive just had a good slow runout and filled up with shell vpower,its improved things and only run on for a second or two,ill carry on running in the engine and hopefully it may correct itself,thanks so much for your knowledge,no doubt more questions to come,cheers Paul.