15 replies to this topic

[1275GT zeemax clubman]

Model:
1275 GT
Year:
1977
Description of problem (please be as in depth as possible):
Just entered my mini in for its MOT. It failed its emmisions on the HC (Hydrocarbon Levels). The max being 1200 ppm and my best result being 1800 ppm. I had a mobile engine tuning guy today to check everything over. He believes the carb is fine and has correct jets and needles. He thinks it must be something inside the engine.

Any non-standard parts that might be involved with the problem?

I think the issue might be linked to the Piper Cam BP285 Scatter. (The tuning guy didnt know about the exact specs of the cam) The engine also has JE race pistons, carrillo race conrods and all the usual little mods. It is a single carb but probably not the cause of the issue.

If what other people I have phoned say, the scatter cam is likely to be the cause of the issue. I am willing to remove said item and replace unless someone thinks this is not the problem. So I suppose I am asking for advice on its replacement. I want to retain the engine as a fast road engine as it is a second vehicle for fun, would just replacing it with the BP285 non scatter solve my issues? Or are there any other cams that would be recomended over this model number or make.

Many thanks

Jason

[L400RAS]

Replacing the cam is an engine-out job on a 1275 (1293) large bore. Have you considered simply turning the mixture screw down to pass the MOT, then turning it back up ...?

[DannyTip]

What are your tappets set to? Setting mine to a larger gap with a kent 286 made a big difference.

[1275GT zeemax clubman]

Having the engine out isnt a problem, out and back in, in a day. Tappets have been reset today by the tuner. He says that the engine is not running correctly at all. When he has his meter in. Starts the engine and leaves it on tick over, the meter starts at say 250ppm and then begins to rise and then eventually gets to say 1800 + ppm. It will then begin to settle down and then back up again. When he revs it to... say 2000 rpm which is probably what the MOT guys will do because it fails at tick over it gets even worse maybe up to 3500ppm.

Tried the mixture screw. The guy at the MOT test did 3 different emmissions tests having fiddled with the mixture screw. The best result being the 1800 ppm.

I dont mind changing the cam shaft. If it solves the problem! I built the engine about 3 years ago... it only passed the MOT the first time because the tester fudged it. The tester this time wont! It also drinks fuel at such a rate (throwing it neat out the exhaust) it costs a fortune to run. Spend the money now and I will reduce it in running costs.

I would try the tappets, but I would have to pay £35 + Vat for every time matey comes and checks it.

Thanks for your comments.

Jason

Edited by 1275GT zeemax clubman, 12 August 2010 - 08:32 PM.

[Pauly]

As said, lean the mixture out until the readings come down. Then ask nicely if the tester can look the other way while you richen it up again.

If its drinking fuel then its running too rich anyway, have you ever had it RR tuned?

[1275GT zeemax clubman]

No I havent. Finding a rolling road in Somerset seems to be tricky. The tuner seemed to think that the carb was fine and was set up correctly. Could it be that a valve isnt seating properly? Im going to get hold of a compression tester hopefully this weekend and make sure its not leaking on a valve. I dont want to take the head off just to look!

What are other peoples experience with scatter cams? I am assuming that actually having checked the timing and setting it up correctly when I rebuilt the engine a year ago that it shouldnt be causing this sort of problem.

Jason

[Turbo Nick]

i know my mate had a 300deg scatter cam and had no issues with the emmissions test.

I'd suggest leaning it out while connected to the tester and remember how many turns you do it so you can reset it when you get outside.

[1275GT zeemax clubman]

Yes i think I am going to do as most of you suggest! Just spoken to the tuner and he said that it will get it passed. He does have a suspicion though that it is miss firing even though he's checked the timing, distributer etc. Obviously I want to get it passed on the 10 day free re-test period. I think i will then try and solve the issues after.

Jason

[samsfern]

i thought a scatter cam was suppose to make it a bit more efficient on idle? Am i right in saying hydrocarbons are unburnt fuel? Does the car smoke at all?

Edited by samsernie, 13 August 2010 - 01:36 PM.

[Cooperman]

The trick used to be to turn the tickover up to around 1800 rpm, lean off the carb so that it would only just run and open up the valve clearances to 0.018". That was a trick I was told, although I have never had to use it (yet).
I got that from an MGB specialist as MGB's also can have that problem with SU carbs and high-lift, high overlap cams.
Apparently the Triumph Dolomite Ownersw Club issued a directive to their members to do something very similar. It's an allowable thing to do at the MoT station as nowhere is the tickover mandated at a specific figure.

[aavayro]

I had the same poblem with my 1293 emissons!, has itgot a 3 to 2 steel type manifold?, Failed due to high emissions.. We changed steel manifold an fitted a cast iron british leyland maniflold belived to be from a 1991 cooper and adjusted the fuel mixture (weakend). Took back for retest still 700 hc but down from 1200 hc, argued the fact that we could not weaken any more and that rebored minis with high compression heads was never made to be subjected to emission testing, then the garage owner allowed the car to pass on condition that we did not sell it.

Emission testing on Classic cars is not a 100% requirment and that MOT garage can adjust to suit

[1275GT zeemax clubman]

Yesterday I changed the carb to the original 1" & 1/4, took it to my local garage and used the hc tester. With the carb set as lean as possible (nut on bottom wound right in) it still was pushin out 3500ppm. The garage owner said for that to happen must be the cam. Fuel and air mix must be going in and being pushed out again without being ignited. He said their didnt sound like a miss fire issue, sounds like its running normally. It must just have a problem with the valve overlap and so loads of fuel is escaping before ignition spark.

This weeks job is to have the cam out. It might even be faulty, miss machined etc. I assume that if I pull the engine out, flip it upside down so the cam followers dont drop having removed the push rods. I can pull the cam out and replace without spliting the engine etc? Its only recently been replaced so bearing etc will be as new. Only done 30 odd miles.

With the lightened pistons, and con rods what would be a good replacement camshaft? Maybe a bit milder than the 285?

Any help would be appreciated.

Jason

[Cooperman]

An MG Metro or a Kent 266 would be a good choice. Those two are almost identical and should put you within limits for emissions.

[Rosslin Racing]

could not see what oil you are running? to "thin" will not help.

[1275GT zeemax clubman]

yes, the oil was a comment made by the garage owner. But I have put the correct oil in and it is brand new. It doesn't smoke, and meets all other items such as CO2 etc. I am going to try one more thing tonight before resulting in taking engine out. Re gap the rockers as suggested, but also replace the capacitor and points and put on one of these leads that boosts the spark. Just to make sure everything electrical is working to its best. I will take it to my local garage and try it tomorrow morning.

If that fails then its definitely time to change the cam.

Jason