Mega low compression in two cylinders - '97 zx7r

Chesh · Derestricted Danger Joined: 02 Jan 2013 Karma :

Hi guys,

A few weeks ago I noticed my bike had no coolant. Which was odd because it had never used any before. I filled it up but over the next couple of days I noticed the bike was getting hotter than usual.

Up until then the bike had never gotten any hotter than to make it rise off the bottom line, unless sat in traffic, but it was now rising up to halfway sometimes. I also noticed it was struggling to start.

Sounds like typical symptoms of a head gasket gone doesn't it Crying or Very sad

I did a coolant flush and replace and let her run up to temp, took her for a ride and she still pulls and feels relatively normal when on the move, except the temperature still rises up to an unacceptable level.

I have just done a compression test and got the following readings:
Cyl 1: 175psi
Cyl 2: 160psi
Cyl 3: 7psi
Cyl 4: 70psi

The compression should be between 149-228psi.

I've read that low compression over two adjacent cylinders means that it's pretty much definitely a blown head gasket, but are these normal numbers for a blown head gasket??? They seem so low that it makes me think I might have done something wrong??

I wouldn't have thought it would even run with compression that low! It doesn't sound like it's running on 2 cylinders.

Any opinions would be greatly appreciated Smile

Thanks!

davebike · World Chat Champion Joined: 15 Nov 2013 Karma :

Yes probably head gasket

There is a chemical test called a 'sniff test' where air from the top of the radiator is drawn though a test solution that will confirm if oil /exhaust gases are getting into the water

Dave
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hmmmnz · Super Spammer Joined: 22 Aug 2006 Karma :

check your oil, is it frothy??
my guess would also be head gasket
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Wafer_Thin_Ham · Super Spammer Joined: 18 Nov 2005 Karma :

69chris · Trackday Trickster Joined: 10 May 2011 Karma :

7 psi ???? im stunned it would run with a figure that low Shocked

does that s/plug looked 'steam cleaned' ?

where are you ? if your nr swindon i have a block tester so checking would take minutes Thumbs Up

Chesh · Derestricted Danger Joined: 02 Jan 2013 Karma :

Wafer_Thin_Ham · Super Spammer Joined: 18 Nov 2005 Karma :

69chris · Trackday Trickster Joined: 10 May 2011 Karma :

Chesh · Derestricted Danger Joined: 02 Jan 2013 Karma :

Apologies for the delay in update but I've only just got round to doing the sniff test.

I've just done it three times and the colour of the fluid didn't change at all. After the second test I even started to think that the fluid was bad, so I held it by the exhaust and squeezed the bulb and the fluid totally changed to green, so I know the fluid's good.

What does this mean!!?? The bike's been sat for the past few months and was an absolute pig to start (yet another sign of the headgasket going!) I almost want it to be the headgasket because at least then I would definitely know what the issue is!

Should I take it to a garage and get them to confirm or deny the headgasket having gone? I was trying to avoid taking it anywhere, particularly as the insurance is up in like 3 days and I don't want to have to renew it if the bike's bust!

This is annoying. Any help at all would be massively appreciated.

Robby · Dirty Old Man Joined: 16 May 2002 Karma :

You need the head off to diagnose anyway.

Could be head gasket, could be a ruined valve or 4. Could be a broken ring, but that is less likely.

No point renewing the insurance until you have it fixed.

Chesh · Derestricted Danger Joined: 02 Jan 2013 Karma :

Hi Robby, thanks for your reply!

Why do I need the head off to diagnose? Is it just to make absolutely sure what has happened?

Is there a way I can check for a ruined valve in any way other than removing the head? For obvious reasons, I don't want to have to remove the engine if I don't have to!

How much of a job is removing the engine on these bikes? On a scale of 1 to 10, how big is the job of replacing the head gasket? I'm not afraid to get stuck in, but after pissing around with cars for years, I try to do as little work as possible!

Robby · Dirty Old Man Joined: 16 May 2002 Karma :

By the sound of it, your problem is most likely head gasket, with a valve problem after that. You need to get the head off to get a good look at the valves or to see the head gasket.

There is of course the possibility that you cocked up on the diagnosis. If it isn't using water any more, and seems to run fine, redo the compression test. if you didn't have the tester screwed in properly on the low compression pots then it would give a low reading.

lihp · World Chat Champion Joined: 22 Sep 2010 Karma :

Regardless of what fault it turns out to be, with compression values that low the head needs to come off regardless of what the fault is.
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stevo as b4 · World Chat Champion Joined: 17 Jul 2003 Karma :

Agree that the head needs to come off for full diagnosis. But have you tried a wet compression test just to see what the difference if any is?

Be careful not to use much oil, as too much oil in the combustion chamber could cause high compression readings anyway, or if way too much oil is used even hydro lock.

There is also two other tests, one is a leak down test, most useful for confirming head/valve sealing faults, a bit less so for piston/rings though. The other test you could do is a coolant pressurisation test, where you pressurise the cooling system as it would be when the bike is running, and then look for signs of coolant leaks. But in your case with the symptoms you mention it would be unlikely to tell you anything useful.