sudden rattling noise engine and one cylinder with only 50% of the compression pressure

A simple way to establish where the compression is going is to rig up or buy an adaptor that allows you to blow air from a compressor into the plug hole, set the engine to tdc firing stroke for that cylinder (valves should be shut) blow the air in and listen, to establish where it comes out, three likely places : inlet, exhaust or engine breather. Indicating which part is faulty, if the air is coming out of the breather then the fault may be piston/rings or an internal crack, if inlet or exhaust air loss then it is a bent or burnt valve.

A burnt valve will not noticeably alter the valve clearances, a slightly bent valve would only make a tiny difference to valve clearances, so if you know what they were before then it could give a guide, but air blown in is the quick and easy way to establish where the problem is.

from your description a foreign body has made its way through the engine bending valves on the way, or the head of a valve has fallen off.

If the cambelt had slipped, then all cylinders would be affected.

It's going to be internal to that cylinder. Head off.

Telling us what car it is might help.

Well,

Any hope of it being a slight small problem seems to be inappropiate. I allow myself to go throught various options, a leak-test had entered my mind, but you need the tools. Hopefully I find someone with an endoscope, if it can detect the fault.

A foreign object inside could have bent the valve, indeed.

Despair setting in ... I'm only a poor amateur ...

Thanks for all advice,

edwin

18 kg/cm² is 255 psi!!!!

There is no way on god's green earth you have that much cranking pressure on a stock petrol engine. Either the gauge is faulty or the bores are awash with oil or you misread the dial but anyway, it's pretty academic trying to guess what's wrong with the engine. A leak down test will tell whether it's top or bottom end. It's perfectly conceivable that one cylinder has been very low on cranking pressure for a long time if you haven't tested it before and the rattle is just the final death throw of something that's been broken for ages.

Hi Dave,

Well, I've measured it two years ago all four cylinders at 18 bar, then after having revved up too high to avoid being hit by a passenger bus, the gauge measured 3x 13 bar and one cylinder 16 bar. Fuel consumption rose substantially ( 30% more consumption : 5 l vs. 7-8 l ) and power diminished.

Now after having been very gentle on the throttle for two years apparently it's at 18 bar again, except 9 bar for the cylinder that is possibly damaged. I agree that cylinder could have had low pressure for a while already. But I don't think the gauge is faulty. Power and fuel mileage corresponded to high pressure two years ago.

It could be oil causing high pressure but the engine is not consuming any significant amount of oil. Maybe carbon deposit ?

A small hope is that any loose objects rattling in cylinder #1 could be retrieved without opening the head/engine, possible with a vacuum cleaner and a plastic tube through the plug hole after determining with an endoscope what it is and where it lies on the piston ...

A new compression test and leak test is an option for next week, but not before I changed the cambelt, it's really worn out.

Has anyone suggestions for a maintenance and repair manual available through Amazon or similar channels ? I don't live in the UK. It is a Mitsubishi Space Star, which has already been strangely behaving before frequently.

Thanks again, I really appreciate your attention.

Edwin

A small hope is that any loose objects rattling in cylinder #1 could be retrieved without opening the head/engine, possible with a vacuum cleaner and a plastic tube through the plug hole after determining with an endoscope what it is and where it lies on the piston ...

That won't cure the compression loss.

A new compression test and leak test is an option for next week, but not before I changed the cambelt, it's really worn out.

Don't waste your money changing the cambelt before the head has been off, the engine is almost certainly scrap.

Steve

Steve,

I tend to hope thay the compression loss is temporary, I've had it before, the rings got stuck or something.

But you offer a realistic and practical approach.

The problem is I have not enough money to buy anything else, and the car isn't worth anything anymore on the market.

It is a pity, because the high compression on the other cylinders looked promising for the future performance and low consumption.

Thanks,

edwin

Helo,

Still an update from me on this topic :

Some years ago, I drove this car on a speed limiting ramp and also started hearing a rattling noise.

It surfaced that the bearing on the shaft next to the clutch ass'y had broken off with a piece of the gearbox housing without this impeding operation of the car, engine or gearbox.

It was repaired within warranty period, but it took a while before the dealer agreed to look into it.

Since I drove up an elevated parking strip next to the road last thursday, and maybe me not pushing the clutch while doing this, the same thing could have happened.

To check wether the rattlig noise I heard thursday stops when pressing down the clutch, I will still have to replace the very worn cambelt first. If the engine is total loss, I can always give the new cambelt to someone nearby having the same car.

Any more suggestions ? MTIA

I hope you don't think about me being too unexperienced to post on this NG, but there is almost an infinity to learn for me.

Thanks again,

edwin

Have you actually established whether the engine is running (or not) on the cylinder you suspect?

I'm beginning to smell troll. Never quite enough details offered and no clarifications. As for getting a broken gearbox housing repaired under warranty due to smacking a speed bump, well.....

Tim

Hi Tim, Mr.Cheerful,

I understand it is a bit unclear. But there really is a problem. I am not waisting your time, just trying to establish some insight.

As for details and clarifications, there is just my experience and it is limited. So if there are details, things omitted, it is not intentional.

The speed bump was probably responsible for the damage, but I did not realize this until long after the gearbox was changed. The descending part, I noticed, was too steep and was corrected later. I could have sewed the local authorities, with what I know now.

Mr.Cheerful,

Since there is a rattling sound, something must be wrong. I will change the cambelt and try to find an endoscope. And indeed, the reduced compression pressure on cylinder #1 could have existed a while already. I think all four cylinders are working, but I don't want to cause any further damage.

A further report if anything is discovered will follow, my only possible contribution to this NG.

Thanks again,

edwin

Mr. Cheerful,

I've tried this adaptor and leak test on another car, and the piston set on tdc always jerked to the lower 180? further bottom position. Presumably you have to prevent this from happening by putting the car into high gear.

Well, hopefully I find a reassuring diagnose and possible repair through a leak test.

thanks

It is best to lock the crankshaft still if possible, preferably by locking the starter ring gear on the flywheel, otherwise first gear (not a high gear) and handbrake.

Um, in this instance, surely a high gear? In first gear the cylinder pressure will generate a lot more torque through the gearbox potentially overcoming the handbrake.

Still think it's a troll mind...

Tim

If you use a high gear then there is considerably more backlash, both in the gearbox, the propshaft, the diff and the suspension rubbers, you will find that the engine will turn a very long way before it is stopped by being in a high gear/handbrake on.

Surely for a leakdown test, the backlash doesn't matter. If the car lurches forward onto your foot because it's in a low gear, that does matter.

I still think you're wrong though. Surely in first gear the crankshaft has to turn much further to take up the backlash in the drive train that in top gear? Why should being in top gear increase drivetrain backlash?

I appreciate that since the advent of FWD things are a bit more complicated but in the old days being in top gear would have eliminated all gearbox backlash.

Tim

50 psi down a cylinder is not going to overcome the handbrake and run you over. If the piston is at tdc and held there then there is very little rotational force imparted to the crank in any case. What you don't want is the piston to start moving and get some momementum into the flywheel.

Hello,

At least we're getting somewhere concerning a leak test.

Please do not refer to me as a troll mind. I do realize this posting may appear to be somewhat of a comedy, but i'm serious. I don't think my high gauge is erroneous, 18 bar is high and i hope that i will finally, after 6 years i will discover what is going on with this car.

Some news will be posted as the testing progresses. I ordered a maintenance and repair manual which will arrive next friday.

Thanks again for your attention.

edwin

Okay, I accept that 50psi probably isn't enough to push the car along. Explain why the flywheel can spin further in top gear than in first (when it will take more crank rotation to "wind up" the backlash?

Tim