Technical What compression should each cylinder have roughly around

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Technical What compression should each cylinder have roughly around

Fiatcinquecento

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I have a 90 126 bis. The 704cc, I say is near knackered. She'll turn over and over but no kick. Got it started once and ran rough like the carb need a clean.
Will not start now and I wouldn't be surprised if a piston rings is stuck.
Any insight into this
The previous owner did a head gasket 300 miles before the car was parked up(6 years ago)
 
Hi :) going on what you just said about the head gasket being replaced I would first of all retighten the cylinder head. These little engines create a lot of vibrations because of their design and a newly compressed head gasket looses its seal as the nuts slacken off so need a re-tweek. The manual says after 500 miles but your not far off on an estimated 300. There’s only 8 head nuts but 2 are obstructed by the rocker shaft and 2 more are hidden by the inlet manifold so these two items need to be removed (the latter is water cooled so you’ll need to drain the coolant.

I would also look at the ignition system too if I was you. Check the points out and see if there not pitted (renew if they are) and re-gap them then static time it with a test light so the the crank pulley mark is lined up to the first little arrow on the engine case (the small left arrow). Static timing isn’t as accurate as using a strobe but should be good enough to get you started providing you have a good fuel supply (also check that the pump works) (y)
 
Thanks for your reply, this section is getting a bit quieter with lack of 126's ?
There was new points put on. And the car even started, but was running rough. After a little drive nudging her gently she died out.
After that she will not start, even sounds like low compression. Have changed plugs too

I have a compression tester, and I will test it soon.
How likely is it that the rings are leaking on the bis motor, as I know it's not the most reliable little engine

It's either a engine rebuild, or for roughly the same money, I'll drop a 1108 into it, but this is my last resort.
Thanks again for your words of wisdom gadge!
 
The BIS engine can take a lot of abuse before they finally break. I myself drove one about 100 miles with a blown head gasket an no water and it never sized up. They need plenty of attention to run right however which is why a lot seem to fail as owners don't do the correct maintainance on them such as cleaning the oil filter out or keeping an eye on the points. They hate being laid up and a monthly run - even just ticking over periodically will pay dividends in the long run.

The compression rings are no more likely to be duff than any other car but of course it is an option but will require a total strip down to fix so perhaps your 1100 cc idea may well be a good option too (y)
 
Thanks for your reply, this section is getting a bit quieter with lack of 126's ?
There was new points put on. And the car even started, but was running rough. After a little drive nudging her gently she died out.
After that she will not start, even sounds like low compression. Have changed plugs too

I have a compression tester, and I will test it soon.
How likely is it that the rings are leaking on the bis motor, as I know it's not the most reliable little engine

It's either a engine rebuild, or for roughly the same money, I'll drop a 1108 into it, but this is my last resort.
Thanks again for your words of wisdom gadge!
Petrol over about 6 months old can go bad and cause non running
 
Thansk again for the replys, fresh petrol was put in at the time, it's like there's no compression at all, not 1 cyclinder kicking to go, so I hope it's just the headgasket. Car has 24xxx on it so it's normal enough for these. It's incredibly solid this car, I need a door and that's the bulk of it!

I have at least 4 donor cinqs/seicentos for a full car loom swap, if the engine is buggured, that's what will happen, but I want it to look factory on the outside apart from chrome bumpers
 
IMG_20160924_211143.jpgIMG_20160924_223412.jpgIMG_20160922_144926.jpg
Some photos for ye
 
So I said I would just check the oil again, to see has anything developed, and.... It smells of petrol. It seem like normal oil thickness but a definite smell of petrol off it. Would this indicate the head gasket?
 
On some cars, if the fuel pump diaphragm starts to fail, petrol can get into the engine oil.
 
New fuel pump put in it as well, again car was running ok, then it stopped after 200m of a drive. Won't start now ?
 
Was running sick, even with carb cleaned out and adjusted, my fault for not stating. It's getting fuel, spark, timing and points are 100%. Had it at a local Fiat specialist and he thinks the engine is buggured. He double checked timing and points. I'm leaning towards head gasket now, will compression test it within the hour and will come back with results
 
Didn't get to compression test it, had it setup and there's no power to the car, something simple but I had no room as it's been boxed in. Have to clean the shed then I'll get back to ye
 
Sorry to butt in .. but I noticed the comment about a new fuel pump .. the car ran ok for a while but now doesn't ...

One of the faults with the old style mechanical fuel pumps was that the pump arm would wear a groove in the cam that operates it. When that groove becomes excessively worn it doesn't operate the pump arm/lever properly. Fitting a new pump works for a while until the pump lever wears the groove even more.

A couple of decades ago (at least) I was driving an old V8 Rover to a classic car autojumble when the car began to slow and then cut out .. and then restart. By the time I'd reached the autojumble I'd already decided that it was a faulty fuel pump and bought one at the autojumble which I fitted there and then.

It was fine for 100 miles and then the problems started again .. It was the cam that operates the pump lever at fault - it had a groove worn in it.

A simple check is to remove the old pump and use a torch/mirror to look inside the engine and check the operating cam.

A temporary get you home (or quick check) measure is to remove the gasket between the pump and block - this allows the pump lever to sit a tad further inside to compensate for wear on the operating cam.

Way back when, a home 'fix' was to braze a blob onto the end of the pump arm. This allowed the blob of braze to compensate for wear on the operating cam. The alternative of course was either to replace the worn cam .. or fit an electric pump.

With a mileage of 24,000 on the clock it's difficult to see why the engine should be shot - unless it has been badly neglected/seriously overheated.

As somebody has stated, a dry and wet compression test will give you an indication of the engine's health.

Good luck.
 
To answer the original question, the compression on each cylinder should be 8.6 bar (give or take 0.15 bar).

Gadge is right about retorquing the cylinder head (although the handbook says retorque happens after 600-900 miles... so 750 miles I guess... but it wouldn't hurt to do it sooner as well) When retorquing the bolts you have to do it in a certain criss-cross order, and in two stages; first to 25Nm then to 49Nm
 
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To answer the original question, the compression on each cylinder should be 8.6 bar (give or take 0.15 bar).

Gadge is right about retorquing the cylinder head (although the handbook says retorque happens after 600-900 miles... so 750 miles I guess... but it wouldn't hurt to do it sooner as well) When retorquing the bolts you have to do it in a certain criss-cross order, and in two stages; first to 25Nm then to 49Nm

Yes it definatly needs to be done. I covered about 1500 miles without retorquing the head and blew the gasket. The nuts spun off with the greatest of ease when I investigated it. Because of its design it vibrates a lot and my guess is that when you initially tighten the head down, the gaskets squashes down then settles in which relaxes the pressure on the nuts making them vunerable to working lose. I followed the handbooks advice the next time and happily I'm up to about 160 psi on each cylinder (not sure what that is in bar) after about 2000 miles.

I havnt got the torque fingers to hand but yes it needs to be done starting from the inner ones first and then just work your way out at oppersite ends to the last nut you turned.
 
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