PistonHeads.com Forum

Low Compression

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Discussion

Emanresu

239 posts

13 months

Wednesday 4th October
quotequote all
I’m surprised nobody has mentioned this but only one compression test? And I assume it was dry? What about doing the standard second test with oil in the cylinder?

The first test will tell you if the compression is low. The second will give an indication as to where the problem lies. Then you can do a leak down test for a more definitive answer.

I don’t like to speak ill of other mechanics but it sounds like yours isn’t competent.

Megaflow

6,475 posts

149 months

Wednesday 4th October
quotequote all
klmorrell said:
Why are people assuming the compression data is wrong ? the compression test data is correct, and it has nothing to do with cambelts, but then again why would it have anything to do with the cambelt, which was replaced 12mths ago and has been perfectly fine.

I mean come on think about it.

I have just dragged a 1.4 tonne caravan over the peninnes for 60 miles and 3hrs with no expansion cap on. then the engine lost power and stopped, followed by an low battery light

whats more likely to have happened in those circumstances ? the engine overheating or the cambelt snapping.

I am no mechanic but on opening the bonnet even I knew the engine had cooked itself

my question here was "how likely would there be serious bottom end damage based on what just happened. I had already assumed the head and headgasket were toast and just that would of been a best I could of hoped for.

after doing the compression test and noticing how laboured the engine spun my mechanic suggested bottom end, and low and behold he was right.
People are assuming the cambelt has gone, or jumped a few teeth put in the timing out, because these engines have a proven history of lunching the valvetrain if the alternator drive belt fails.

What happened just before your engine stopped? Yes, the battery light came on, which means the alternator is not charging the battery. Normal causes for this are failed alternator, which doesn't stop the engine straight away, or th driv belt coming off, which can cause the engine to stop straight away if it foils the cambelt.

If it looks like a duck, walks like a duck and quacks like a duck. It's a duck.

bearman68

2,027 posts

56 months

Wednesday 4th October
quotequote all
Megaflow said:
If it looks like a duck, walks like a duck and quacks like a duck. It's a duck.
To be fair, and I mention this in a light-hearted manner, the probability tends towards duck. However in this case, I suspect goose!



(Well I found it amusing)

stevieturbo

12,725 posts

171 months

Wednesday 4th October
quotequote all
You're all quackers

Megaflow

6,475 posts

149 months

Wednesday 4th October
quotequote all
bearman68 said:
Megaflow said:
If it looks like a duck, walks like a duck and quacks like a duck. It's a duck.
To be fair, and I mention this in a light-hearted manner, the probability tends towards duck. However in this case, I suspect goose!



(Well I found it amusing)
hehe
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Boosted LS1

16,605 posts

184 months

Wednesday 4th October
quotequote all
Emanresu said:
I’m surprised nobody has mentioned this but only one compression test? And I assume it was dry? What about doing the standard second test with oil in the cylinder?

The first test will tell you if the compression is low. The second will give an indication as to where the problem lies. Then you can do a leak down test for a more definitive answer.

I don’t like to speak ill of other mechanics but it sounds like yours isn’t competent.
Oil in the cylinder won't have reached normal readings. This engine's goosed or the mechanic's cranking the engine with a spanner.

klmorrell

Original Poster:

18 posts

62 months

Thursday 5th October
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Boosted LS1 said:
Oil in the cylinder won't have reached normal readings. This engine's goosed or the mechanic's cranking the engine with a spanner.
Your getting closer. smile The battery low light on, is another clue, timing belt is on and perfectly timed up,

The mechanic couldn't rotate the engine with the spark plugs out using a spanner/ratchet.

He needed a 2foot breaker bar.

TooMany2cvs

19,872 posts

50 months

Thursday 5th October
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klmorrell said:
The battery low light on
AAAGH! IT IS NOT A "BATTERY LOW" LIGHT. IT IS A "NOT CHARGING" LIGHT. Start to understand and accept that difference, and you might start to understand what you're being told by people who understand what's feasible.

klmorrell said:
is another clue, timing belt is on and perfectly timed up,
Has this ACTUALLY been checked? Pins in sprockets, belt marks lining up? Nothing you've said before suggests it.

klmorrell said:
The mechanic couldn't rotate the engine with the spark plugs out using a spanner/ratchet.

He needed a 2foot breaker bar.
Then how the flying fkerigar did he do a compression test? THIS MAKES NO SENSE.

klmorrell

Original Poster:

18 posts

62 months

Thursday 5th October
quotequote all
I'm sorry but, the light was a "low battery" light, meaning the battery was nearly dead.

the compression test was done with this battery fully charged, this is a 12mth old 760amp silver series battery, after the compression test the battery was down to 244amp

when he tried to rotate engine by hand it was too tight for a normal ratchet, he had to use an extension,

the engine is partially seized, and trying to start a partially seized engine or keep a seizing engine running will quickly drain a battery.

klmorrell

Original Poster:

18 posts

62 months

Thursday 5th October
quotequote all
also the head gasket has blown, so I imagine doing a compression test on a partially seized engine with a blown headgasket could quite easily account for such low psi figures ?

Megaflow

6,475 posts

149 months

Thursday 5th October
quotequote all
klmorrell said:
I'm sorry but, the light was a "low battery" light, meaning the battery was nearly dead.

the compression test was done with this battery fully charged, this is a 12mth old 760amp silver series battery, after the compression test the battery was down to 244amp

when he tried to rotate engine by hand it was too tight for a normal ratchet, he had to use an extension,

the engine is partially seized, and trying to start a partially seized engine or keep a seizing engine running will quickly drain a battery.
There is no such thing as a low battery light... try disconnecting the battery, you can't get any lower than no battery, how many lights do you now have? Yes, none.

The battery light, as you have been repeated told, is a charge warning light, meaning the alternator is not charging the battery.

That means the alternator has failed or the belt to the alternator has failed.

Edit to add: I don't suppose this mechanic is the same one that change the cambelt, and therefore has an interest in making sure it is not a cambelt failure would he?

Edited by Megaflow on Thursday 5th October 10:12

TooMany2cvs

19,872 posts

50 months

Thursday 5th October
quotequote all
klmorrell said:
I'm sorry but, the light was a "low battery" light, meaning the battery was nearly dead.
There is no such thing on any car.

Damn near EVERY car has a "not charging" light, though.

klmorrell said:
the compression test was done with this battery fully charged, this is a 12mth old 760amp silver series battery, after the compression test the battery was down to 244amp
You don't even understand how little sense that makes, do you, let alone how impossible it would be to measure that?

klmorrell said:
when he tried to rotate engine by hand it was too tight for a normal ratchet, he had to use an extension,

the engine is partially seized, and trying to start a partially seized engine or keep a seizing engine running will quickly drain a battery.
There is no way that the starter would turn an engine "partially seized" enough that a sodding great big breaker bar would be needed to turn it with the plugs out, let alone fast enough for any kind of meaningful compression test.

The more you post, the less sense you're making. Just be man enough to admit that half of these things haven't actually been checked by anybody vaguely competent.

GreenV8S

24,946 posts

208 months

Thursday 5th October
quotequote all
klmorrell said:
the engine is partially seized
If you had said that at the outset, the rest of this thread would be redundant. You have already answered your own question. If the engine has seized, the bottom end is stuffed.

The compression test was both pointless (any competent mechanic should have recognised the seized engine immediately and understood the implications) and useless (if the engine isn't spinning freely the results are going to be wildly inaccurate), and if you'd answered questions about how you carried out the test instead of insisting that you both knew what you were doing and it was completely normal, that would quickly have been apparent.

liner33

6,358 posts

126 months

Thursday 5th October
quotequote all
GreenV8S said:
klmorrell said:
the engine is partially seized
If you had said that at the outset, the rest of this thread would be redundant. You have already answered your own question. If the engine has seized, the bottom end is stuffed.

The compression test was both pointless (any competent mechanic should have recognised the seized engine immediately and understood the implications) and useless (if the engine isn't spinning freely the results are going to be wildly inaccurate), and if you'd answered questions about how you carried out the test instead of insisting that you both knew what you were doing and it was completely normal, that would quickly have been apparent.
he did........ kinda

"One of the things the mechanic noticed whilst doing the compression test was how the engine didn't seem to spin any quicker with all the spark plugs removed, the cambelt ect is about 12mths old and is still on and taught.

stevieturbo

12,725 posts

171 months

Thursday 5th October
quotequote all
klmorrell said:
also the head gasket has blown, so I imagine doing a compression test on a partially seized engine with a blown headgasket could quite easily account for such low psi figures ?
Yes, but even a retard mechanic should then know under those circumstances any compression test would be nonsense.

As everyone had been telling you, with the partial bits of ( mis ) information that keep dripping through

Now that we've finally, and painfully extracted some useful information, it does seem the car is fked. Give up on it.

Megaflow

6,475 posts

149 months

Thursday 5th October
quotequote all
But, engines spin faster when they have no compression, taking the plugs out will not increase the cranking speed as it normally would.

Given that he started a thread about low compression, that fact would not have been considered relevant.

This still comes back to the fact engines do not suddenly stop with a blown head gasket or seizing without any other symptoms than a charge warning light. They do however stop straight away due to a cambelt timing issue, which can begin with a charge warning light.

GreenV8S

24,946 posts

208 months

Thursday 5th October
quotequote all
liner33 said:
he did........ kinda

"One of the things the mechanic noticed whilst doing the compression test was how the engine didn't seem to spin any quicker with all the spark plugs removed
But he didn't mentioned the engine needed a breaker bar to turn over or that running the compression test flattened a big battery - that suggests it was taking a huge current which in turn suggests it was turning over slowly (which makes sense for a partially seized engine). Running a compression test on an engine that can barely be cranked over is pointless; it has to be spinning reasonably fast to produce a valid result, and the fact that the engine is obviously partially seized already tells you more than the compression test would have.

Edited by GreenV8S on Thursday 5th October 13:03

Boosted LS1

16,605 posts

184 months

Thursday 5th October
quotequote all
This thread seems to have been a quiz.

liner33

6,358 posts

126 months

Thursday 5th October
quotequote all
Boosted LS1 said:
This thread seems to have been a quiz.
Bit like BBC Only Connect "Quiz show in which connections must be made between apparently unconnected things, where patience and lateral thinking are as vital as knowledge"



klmorrell

Original Poster:

18 posts

62 months

Thursday 5th October
quotequote all


This is the battery charging light , that every cars has ? just want to make sure, its the little picture of a red battery ?