Cam timing & Emissions
Discussion
My westy has a Toyota 4AGE running on Dellorto 45's.
Has a 290 duration cam (Kent Cams T1604) which, I think, is reasonably agressive?
Vernier pulleys, but no markings on them.
Last MOT the garage wound back the idle mixture and it scraped through emissions.
This time they've been wound back and it still won't pass.
Mecahnic thinks cambelt is a bit slack (stretched? Not tight enough?) and he needs to re-time the cams.
Another symptom he mentioned is that the compression is "a bit low" accross the board.
He thinks the exhaust cam is a bit retarded.
(Sound, knowledgeable bloke he's not messing me about or anything)
I think that there may also be a slight leak on the exhaust manifold... could affect CO & Hyrdrocarbons?
Just interested in hearing soem wisdom on the science of cam timing & emissions...
Cheers
Has a 290 duration cam (Kent Cams T1604) which, I think, is reasonably agressive?
Vernier pulleys, but no markings on them.
Last MOT the garage wound back the idle mixture and it scraped through emissions.
This time they've been wound back and it still won't pass.
Mecahnic thinks cambelt is a bit slack (stretched? Not tight enough?) and he needs to re-time the cams.
Another symptom he mentioned is that the compression is "a bit low" accross the board.
He thinks the exhaust cam is a bit retarded.
(Sound, knowledgeable bloke he's not messing me about or anything)
I think that there may also be a slight leak on the exhaust manifold... could affect CO & Hyrdrocarbons?
Just interested in hearing soem wisdom on the science of cam timing & emissions...
Cheers
All that typing...and you never even stated the emissions levels it failed on.
An exhaust leak will very much affect emissions, so much so that if there is an exhaust leak, the test should not be conducted. At least that's what happens here, unless it was a very very minor leak.
Cam timing will affect emissions, as will plenty of other things. But until it's known the emissions levels are known, impossible to suggest a remedy
An exhaust leak will very much affect emissions, so much so that if there is an exhaust leak, the test should not be conducted. At least that's what happens here, unless it was a very very minor leak.
Cam timing will affect emissions, as will plenty of other things. But until it's known the emissions levels are known, impossible to suggest a remedy
stevieturbo said:
All that typing...and you never even stated the emissions levels it failed on.
An exhaust leak will very much affect emissions, so much so that if there is an exhaust leak, the test should not be conducted. At least that's what happens here, unless it was a very very minor leak.
Cam timing will affect emissions, as will plenty of other things. But until it's known the emissions levels are known, impossible to suggest a remedy
Yeah, I don't know the actual results, was a 2 min phone convo this morning.An exhaust leak will very much affect emissions, so much so that if there is an exhaust leak, the test should not be conducted. At least that's what happens here, unless it was a very very minor leak.
Cam timing will affect emissions, as will plenty of other things. But until it's known the emissions levels are known, impossible to suggest a remedy
I think if there is an exhaust leak it is minor, and might not even exist. I mentioned it because during MOT prep I had noticed that bit of soot had been blowing out of the exhaust manifold. I replaced the gasket and used some manifold sealant just in case, so it might not even be relevant. I'm sure he would have picked that up if it was a problem!
So a mildy retarded exhaust cam... theoretically this can affect emissions because?
Its interesting! This car taught me about carbs, and now cams & timing.
Its one of the few things I haven't attempted myself... cambelt & timing etc...
Looks straightforward, but the consequences of getting it wrong are quite severe!
I was going to get the cambelt done in the next few months anyway, so hopefully this will fix the emissions and it will actually be running better than it has while I've had the car!
Its one of the few things I haven't attempted myself... cambelt & timing etc...
Looks straightforward, but the consequences of getting it wrong are quite severe!
I was going to get the cambelt done in the next few months anyway, so hopefully this will fix the emissions and it will actually be running better than it has while I've had the car!
theshrew said:
If the timing is out it wont be running as well as it could even though it still will run. Even if its 0.5 deg out it will make a difference.
1/2 degree out from what ?I defy anyone to actually measure the difference in emissions from a 1/2 degree change in cam timing.
CO 8.88 vs 3.5
HC 5496 vs <1200
on fast idle test.
Exhaust gets very hot very fast, chap thinks that either ignition or valve timing is too retarded.
Think I'm going to poull it back somewhere where they can adjust carbs, ignition map and cam timing all together on an RR, and ask them to find me a nice place between emissions and performance.
HC 5496 vs <1200
on fast idle test.
Exhaust gets very hot very fast, chap thinks that either ignition or valve timing is too retarded.
Think I'm going to poull it back somewhere where they can adjust carbs, ignition map and cam timing all together on an RR, and ask them to find me a nice place between emissions and performance.
Glade said:
CO 8.88 vs 3.5
HC 5496 vs <1200
on fast idle test.
Exhaust gets very hot very fast, chap thinks that either ignition or valve timing is too retarded.
Think I'm going to poull it back somewhere where they can adjust carbs, ignition map and cam timing all together on an RR, and ask them to find me a nice place between emissions and performance.
I've built race engines with 300+ degree cams that managed to get idle HC readings of 200 or so and normal CO ones so your cam duration is not the issue if everything mechanical is in good order. Your massive HC readings show huge amounts of fuel not getting burned so a compression test is the first port of call to make sure no valves are bent or severe bore wear and then do cam and ignition timing checks if comp readings are even across the board.HC 5496 vs <1200
on fast idle test.
Exhaust gets very hot very fast, chap thinks that either ignition or valve timing is too retarded.
Think I'm going to poull it back somewhere where they can adjust carbs, ignition map and cam timing all together on an RR, and ask them to find me a nice place between emissions and performance.
I found out those test results were from the first MOT test as was, without any setup. So being so high might not be so crazy.
I had the carbs stripped and re-built over winter, then just put them on and it ran - obviously very rich.
He didn't seem to have results after any adjustment, only that it still failed when he backed them right off.
He said compression is even across all cylinders and doesn't think there is any valve damage.
I had the carbs stripped and re-built over winter, then just put them on and it ran - obviously very rich.
He didn't seem to have results after any adjustment, only that it still failed when he backed them right off.
He said compression is even across all cylinders and doesn't think there is any valve damage.
AER said:
It's just running really rich. Zilch to do with cam timing or ignition, albeit they will have a small effect. Your carbs need some further attention.
Are they properly balanced? One cylinder not out to lunch or something?
Spot on, may be a float height issue, if the mixture screws are not leaning your idle out, wind the mixture screws in clockwise gently to the stop then wind them back out 2 full turns, this is def fuel related.Are they properly balanced? One cylinder not out to lunch or something?
Car is in with someone who knows what they are doing.
Cambelt changed, and cams re-timed.
Carbs weren't balanced. Only drawing through one carb at idle.
Fuel pressure too high making it difficult to start because too much fuel.
Had it on a gas analyser and the HC's are really good for an engine with those cams and CO is OK too...
Hopefully have the car back by the weekend!
Cambelt changed, and cams re-timed.
Carbs weren't balanced. Only drawing through one carb at idle.
Fuel pressure too high making it difficult to start because too much fuel.
Had it on a gas analyser and the HC's are really good for an engine with those cams and CO is OK too...
Hopefully have the car back by the weekend!
Glade said:
Car is in with someone who knows what they are doing.
Cambelt changed, and cams re-timed.
Carbs weren't balanced. Only drawing through one carb at idle.
Fuel pressure too high making it difficult to start because too much fuel.
Had it on a gas analyser and the HC's are really good for an engine with those cams and CO is OK too...
Hopefully have the car back by the weekend!
Enjoy Cambelt changed, and cams re-timed.
Carbs weren't balanced. Only drawing through one carb at idle.
Fuel pressure too high making it difficult to start because too much fuel.
Had it on a gas analyser and the HC's are really good for an engine with those cams and CO is OK too...
Hopefully have the car back by the weekend!
sweet engines Jap Twin Cams 
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