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Discussion Starter #1
okay iv got an alfa 33 1.7 carby
iv got low compresiion on the left side cylinder heads .....my mechanic says i need new valves put in apparently its running ruff because i havent put the additive petrol iv been using straight unleaded petrol 98 ....as i drive my 33 at low speeds it starts stuttering and feels like it guna dies but when i go 60 or over it goes away but when i am slowing down it returns it from the left side i can feel it :( can anyone tell me what it is and do i have leaded valves in my cylinder heads or did my 33 series 2 1988 come out with unleaded valves thanx alfio
 

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All boxer engine can handle unleaded fuel as they have hardened valve guides . So any damage to the valves was caused form another cause , probably bad timing or worst , worn tappets.
 

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Rough engine run in the lower RPM range might be caused by trhottle/mixture
imbalance between the left and right carbs.
 
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do a cylinder leak test to determine where you are losing compression before taking it apart.

a compression check will tell you if one or more is down but not where you are losing it.


turn the engine until the faulty cylinder is at tdc, piston at the top and ready to spark. VERY important that the cylinder is in position ready to spark as the piston comes up twice per cycle. on the wrong cycle the valves will be on overlap and partially open.
now insert into the spark plug hole the home made tool like i made which consists of the bottom half of a spark plug (just the threaded part and nut section) with an air-line fitting welded onto it.
so you now have the ability to put your own compression into the engine with it static.
make sure first though to either lock the flywheel if possible or get someone to put it in gear with the brakes hard on, this will stop the pistons going back down if you haven't quite got it 100% at tdc when the next stage comes...
connect the air-line up and see where the air comes out.
if it's coming out through the exhaust then the exhaust valves are the problem.
out through the carb and it's the inlet valves.
take out the oil filler cap and if it's through there then suspect the pistons/rings/bores.
also check the water expansion tank as if it's bubbling in there then the head gasket/cracked head could be the culprit.

also don't forget to check the plug hole next door as it could be simply blowing between the 2 cylinders.

if you do these checks to determine where you are losing the compression then you will have a clear idea wherer to look when taking it apart :thumbs:





would very much reccomend checking all the items described above, could well be the cause of poor running.
 

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Discussion Starter #6
hey guys thanx for you replys this problems seems to puzzle me alot....
iv recently had my carbys overhauled jets and everything new gaskets put in em also
my mechanic has done a cylinder pressure test on the left side and said im getting low psi reading of 60 to 70psi on the left side ......on the other hand my right cylinder heads is getting 140psi .... so he told me im getting to much air in throught the left side cylinder but im still puzzled as what it could be???? tappets ,valves,valve seals,anythng else thank you guys
 
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hey guys my father has corrected me and told me he done a presure test where the spark plugs go ???
yes, that's where you do a compression test.
you really need to do the cylinder leak test as i described earlier to pinpoint where the compression is being lost though ;)
 

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perfect guideline for a check! i will keep this in mind.
thank you kev.

do a cylinder leak test to determine where you are losing compression before taking it apart.

a compression check will tell you if one or more is down but not where you are losing it.


turn the engine until the faulty cylinder is at tdc, piston at the top and ready to spark. VERY important that the cylinder is in position ready to spark as the piston comes up twice per cycle. on the wrong cycle the valves will be on overlap and partially open.
now insert into the spark plug hole the home made tool like i made which consists of the bottom half of a spark plug (just the threaded part and nut section) with an air-line fitting welded onto it.
so you now have the ability to put your own compression into the engine with it static.
make sure first though to either lock the flywheel if possible or get someone to put it in gear with the brakes hard on, this will stop the pistons going back down if you haven't quite got it 100% at tdc when the next stage comes...
connect the air-line up and see where the air comes out.
if it's coming out through the exhaust then the exhaust valves are the problem.
out through the carb and it's the inlet valves.
take out the oil filler cap and if it's through there then suspect the pistons/rings/bores.
also check the water expansion tank as if it's bubbling in there then the head gasket/cracked head could be the culprit.

also don't forget to check the plug hole next door as it could be simply blowing between the 2 cylinders.

if you do these checks to determine where you are losing the compression then you will have a clear idea wherer to look when taking it apart :thumbs:





would very much reccomend checking all the items described above, could well be the cause of poor running.
 
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