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Old 2 Weeks Ago   #1
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What compression should each cylinder have roughly around

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)
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Old 2 Weeks Ago   #2
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Re: What compression should each cylinder have roughly around

@gadge should be a good start here.

Figures are reliant on so many factors

Comparing your 2 cylinders against each other .....
Dry...

Wet...

Wet improvements mean a poor seal

Charlie
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Old 2 Weeks Ago   #3
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Re: What compression should each cylinder have roughly around

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. Thereís 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 youíll 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 isnít 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)
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Old 2 Weeks Ago   #4
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Re: What compression should each cylinder have roughly around

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!
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Old 1 Week Ago   #5
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Re: What compression should each cylinder have roughly around

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
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Old 1 Week Ago   #6
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Re: What compression should each cylinder have roughly around

Quote Originally Posted by Fiatcinquecento View Post
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
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Old 1 Week Ago   #7
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Re: What compression should each cylinder have roughly around

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
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Old 1 Week Ago   #8
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Re: What compression should each cylinder have roughly around

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Old 1 Week Ago   #9
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Re: What compression should each cylinder have roughly around

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?
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Old 1 Week Ago   #10
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Quote Originally Posted by Fiatcinquecento View Post
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?
Unburnt fuel...
You state plugs/points are ok..

So maybe flooding from carb..
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Old 1 Week Ago   #11
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Re: What compression should each cylinder have roughly around

On some cars, if the fuel pump diaphragm starts to fail, petrol can get into the engine oil.
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Old 1 Week Ago   #12
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Re: What compression should each cylinder have roughly around

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 😅
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Old 1 Week Ago   #13
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Quote Originally Posted by Fiatcinquecento View Post
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 😅
Thought you said it was running sick..as in carb trouble?
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Old 1 Week Ago   #14
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Re: What compression should each cylinder have roughly around

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
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Old 1 Week Ago   #15
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Re: What compression should each cylinder have roughly around

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
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