75 replies to this topic

[calgibb]

Hello,

 

I have just completed an engine swap on a Mini from a 998cc (carb) to a 1275cc cooper (injection covered to carb during swap) engine, I have installed all of the parts I think I needed to and set up everything I know how to in order to get the engine running however after adjusting everything I could think of I have had no luck. I decided to test the compression as I have spark and fuel, when i find that cylinder 2 and 3 have around 30psi I assume its the head gasket like as I have had that problem previously so that has been replaced. In comes the mechanic, after a little bit of investigation he discovers that both cylinders are actually sucking are in rather then expelling air when covering the spark plug holes.

Basic mechanics has taught me the order goes suck squeeze bang blow so the piston should pull down, the inlet valve opens followed by the piston pushing up and the spark plug igniting the gas forcing the piston back down then exhausting.

However these two cylinders don appear to be working in that order, they appear to be pulling the piston down, sucking in exhaust pushing the piston up and exhaling the exhaust out of the inlet.

Both the Mechanic and myself have agreed we think it is the wrong cam shaft however I am coming to The Mini Forum to see if there is anyone out there who has suffered this and know its something completely different.

 

Thanks in advance

 

Callum

[sledgehammer]

This is a guess , 

 

I would check the valve lash / gap , also check compression with throttle open & all plugs out

 

has the cam timing been changed ? (new chain / sprocket) - if so , check it is correctly timed

 

firing order should be 1342 , dizzi anti clockwise , number one cyl at 1 oclock

 

if head gasket has gone between 2&3 , there may be no compression on those cylinders , so I would ignore the sucking plug holes for the moment

 

look at simple cheap things first ,

 

my guess is head gasket - (if the cam timing has not been adjusted from a known to run engine)

 

or badly adjusted valve lash / gap

Edited by sledgehammer, 21 October 2015 - 11:47 PM.

[calgibb]

The guy i bought it from said it ran fine in the car he took it from.

I have checked the compression, 120 in 1 and 4 but almost nothing in 2 and 3

As far as i am aware nothing has been changed however if it was timing would all cylinders not be off?

Firing sequence is correct.

Its a brand new head Gasket, literally bought and fitted today even thought the old one seemed fine upon inspection.

As you look at it with the rocker head off you can see that the valves aren't opening correctly as when the inlet is open it should be the exhaust and the exhaust when the inlet should be open but only on cylinders 2 and 3. 1 and 4 appear to be running close to perfect.

[Dusky]

Remember that the valves on a mini are arranged like this :

EX-in-in-ex-ex-in-in-ex

[calgibb]

I am aware that the valves are ordered like that, the mechanic I mentioned has worked on a lot of minis over the years.

[nicklouse]

Ok the cam shaft.
for it to be the wrong one it would have to be on that fits the block but uses a different head.

can you think of any? nope. dont think that it will be the Cam.

check your clearances. double check your firing order.

[Carlos W]

Re-set the tappets.

 

Have you had the cam chain off, or the cam out at all?

[KernowCooper]

Another engine that was running right before being taken out! I would have had the head off and checked for the gasket gone between 2 and 3, and if your current mechanic thinks it the wrong camshaft then change your Mechanic thats a rookie statement and not one made by a mechanic.

[midridge2]

You have said that you have replaced the H/G, if you still have low compression its possible that its the head cracked between cylinders.

[Yoda]

 if your current mechanic thinks it the wrong camshaft then change your Mechanic thats a rookie statement and not one made by a mechanic.

 

I agree. Find someone who knows what they are actually doing.  

 

you need to first double check your valve clearances and if OK remove the head again and check that the gasket has seated properly and have the head inspected for cracks. also check the block deck, Most cases like this i have looked at has usually been a gasket issue or burnt cylinder wall between the two cylinders.

 

Forget the issue of air sucking in for now, that is probably a red herring. Your suck squeeze bang blow theory works for one cylinder, but if air can move between the cylinders via a crack, erosion or open valves then think again. blow might just become suck!!!!!

[dklawson]

As above.  Since you have removed the head, you must reset the valve clearances.  If that does not raise the compression values, do a leak-down test to determine where the problem is.

[dyshipfakta]

Timing or clearances need sorting

[dklawson]

If the cam and/or timing components were not changed, and if the timing chain has not slipped, the valve timing will not be changed.  The ignition timing does not affect compression test readings.

[calgibb]

I think the sucking is relevant due to the valves not opening in the correct order, the engine effectively has 2 working correctly the other two are creating an engine brake.

I have reseated the H/G twice now and replaced it once with the correct torque. A crack in the Head wouldnt explain why the engine is sucking in exhaust and blowing out the inlet by visual inspection of the tappets while turning the engine over bit by bit.

The timing clearance has been checked twice.

The mechanic does know what he is doing he has about 20 years experience, a lot of experience with Minis over the years and is now running 2 garages. To be honest I am thinking I don't trust the guy I bought the engine from because there is nothing stopping him swapping the cam if he wanted the one off the engine I bought as he also took of the injection system hence the conversion to carb.

 

As above.  Since you have removed the head, you must reset the valve clearances.  If that does not raise the compression values, do a leak-down test to determine where the problem is.

I am doing a leak test tonight, the mechanic is bringing the relevant testing tools as he didn't have them with him last night.

[Carlos W]

I think the sucking is relevant due to the valves not opening in the correct order, the engine effectively has 2 working correctly the other two are creating an engine brake.

I don't know enough about the A series engine to say whether or not there's another cam which would fit, but has a different firing order. 

 

But I have my doubts.

 

If the cam timing was a mile out it would reduce compression on all cylinders. 

 

What method are you using to set your valve clearances? Did you lap in the valves when you had the head off? Any evidence of the valves not seating correctly