15 replies to this topic

[crf150]

if I'm just doing the standard dry compression test how can I tell if the bottom end is gone ? Would i be able to tell if it is the bottom end or the head gasket gone from the compression test ? Would it actually be drivable if the bottom end has gone ?

Thanks

[minimuk]

if I'm just doing the standard dry compression test how can I tell if the bottom end is gone ? Would i be able to tell if it is the bottom end or the head gasket gone from the compression test ? Would it actually be drivable if the bottom end has gone ?

Thanks

dry test and all readings are within 10% will tell you gasket is ok,.........wet test will do both, but will tell you also for wear of the piston-rings if there is any.......

[crf150]

What would the compression test be if the bottom end is gone ? Or would I have to do a wet test as well to check that ? (Don't really want to do a wet test, because its not my car and I'd jut rather not :) )

[Fast Ivan]

by bottom end I assume you mean the piston rings/bores?
compression should build up quite quickly in an engine thats ok, a low compression reading on the first stroke followed by gradually increasing pressure could indicate piston ring/bore problems.
A low compression reading on the first stroke that doesn't increase on succesive strokes indicates a valve problems or head gasket blown.
You will need to add a drop of oil to the "offending" cylinder, if there is one, and if this improves the compression readings then this is another indication of piston ring/bore problems, no change points to the valves or head gasket.
Two low readings in cylinders next to each other is almost certainly a blown gasket.

[Fast Ivan]

as and edit to the above - it might help if you explain what gives you cause to do the compression test, for example is the power down? are you burning oil/blue smoke?
Oil on the spark plugs?

[crf150]

Well I'm buying it off of a friend and he said that it is missing on #3 and #4 you can sort of hear it on this video but I'm unsure, http://m.youtube.com...h?v=v1I8arPhiMs

[crf150]

He also said that he has replaced most of the electrical side. Ht leads, ignition coil, spark plugs, dizzy cap etc

[Fast Ivan]

well if he's definitely replaced the ignition side as described and theres definitley a spark, no loss or burning oil, then going on what you have said I would suspect a head gasket failure. The compression test will give more info. though its more common that the gasket goes between 2 and 3.

[jaydee]

A compression test has nothing to do with bottom end which is main bearings etc..It will tell you if you have poor compression due to faulty head gasket, worn piston rings, worn/badly pitted valve seats.

[Cooperman]

It always amazes me when people buy an unknown engine and just fit it, or just fit a head gasket, without taking the main and big-end caps off to check the bearing shells and crankshaft and taking the pistons out to check rings & bores. It always seems that they come back on here asking for advice on low oil pressure, smoking, rattling, etc., within a short space of time.
With the engine out it's so easy to check and replace parts as necessary.

[crf150]

I haven't actually bought anything yet, I'm meant to be buying it off of a friend, but I wanted to buy it quick because he has it advertised and I don't want it to get sold. But I wanted to check to see if it would be the head gasket or anything else because at the moment I have only got enough for the car and I don't want to find out that it is something really bad and I haven't got any money to fix it.

[minimuk]

I haven't actually bought anything yet, I'm meant to be buying it off of a friend, but I wanted to buy it quick because he has it advertised and I don't want it to get sold. But I wanted to check to see if it would be the head gasket or anything else because at the moment I have only got enough for the car and I don't want to find out that it is something really bad and I haven't got any money to fix it.

fair play checking it out first wiv us on here...., but agree fully wiv cooperman.
question:.is the engine ticking over, if so can you hear any clonking or irratic noises from the bottom of the engine?

Edited by minimuk, 04 December 2012 - 09:20 PM.

[crf150]

I haven't actually bought anything yet, I'm meant to be buying it off of a friend, but I wanted to buy it quick because he has it advertised and I don't want it to get sold. But I wanted to check to see if it would be the head gasket or anything else because at the moment I have only got enough for the car and I don't want to find out that it is something really bad and I haven't got any money to fix it.

fair play checking it out first wiv us on here...., but agree fully wiv cooperman.
question:.is the engine ticking over, if so can you hear any clonking or irratic noises from the bottom of the engine?

I haven't actually been to see it yet, but I am going to this week(hopefully) I'm better of checking on here first because I'm pretty sure that all of these mini minds will know what would be wrong with anything to do with a mini if I asked ! :) there is a video up a bit if you haven't already seen it, I could really hear a lot in the video but I'm sure others might be able to pick out something.

[Fast Ivan]

Looking at your previous topic and your profile I can see that your seeking advice about a mini you might buy thats not firing on all cylinders for some reason and that your concerned it might be somthing serious that requires the engine to be rebuilt.
So we are going to need some more information.
What makes you think that the bottom end of the engine is knackered? is it just the not firing on all cylinders? or do you have more information than this?
What does the owner think of the engines bottom end? does he have reason to suspect problems there?
How many miles has the engine done?
Has it had regular oil changes?
Has the red oil pressure light came on?
The video you have posted doesn't seem to work.

Check that there is definitley a spark once this is confirmed then do the compression test.
Lets get these questions answered and go from there.
An engine not firing on a couple of cylinders does not mean the bottom end is knackered, though it could be the pistons rings/bores and this is an engine out job, but lets not assume that just yet.

Edited by Rob Mac, 05 December 2012 - 09:53 AM.

[crf150]

Well it was just something that I suspected, all I know is that it isn't firing on cylinders 3 and 4(that's what he said) I should be going to view it sometime this week so I will ask him if its had oil services etc...

If you just go onto YouTube and type in Austin mini 1275 drive, it's a gold mini with a zee max kit on it. not too sure how many miles it has got on it, originally it was a 850 but the person that had it before him put lots of different things on it, it has had a engine change with a 1275 engine and he said that it says 4k on the clock but me and him said I'm pretty sure that it hasn't got that little on it.

Hope you can get something from this :)