1990 ZXR250 low compression on 2 cylinders. Head gasket? Valves? What?

[ZXCharlieR]

Hi Guys,

Here I am again, just the end of the first day and asking for some help, sorry!!

I will explain the scenario:

I bought this great little bike with the problem, so no point in me complaining.

The problem is that she wont start off a cold start, I did a compression test and the results are Cylinders 1 & 3 No Compression, Cylinders 4&5 Were fine, this is the "detailed" description I got from the previous owner:

"Number 1 and 3 had no compression so I squirted a drop of oil in each cylinder and got 50 psi where as 1 and 4 had 150 psi straight away. when the engine was warm it would start fine but the next day when cold it wouldn't go."

Hope that's "enough" information as it's all I got, just need some help in what I am supposed to look at, I am not a mechanic and I am certainly not likely to pay a mechanic at £65 the hour to tell me the same as this guy has.

Anywho ... I will do a full leak test when I have the time but any ideas would be great as I don't want to have to strip it and then realize, after spending 100's, that it was just something trivial, like, er, rings.

I have an idea that it could be rings or valves, please give me some insight as to what to look for and I'll post progress, even a video if it all goes as to plan.

Another quick question, is the manual on ZXR250 Riders Facebook page the same for the 1990 model?, it says it's for the 1997 model.

Thanks to everyone in advance!!

Charlie

[ducatilover]

Valves, rings, headgasket or holed piston/block.

There are your options

[ZXCharlieR]

Thanks for that!!

Does anyone know if the 250C model block and head would fit the B model as I have seen one on ebay and the parts for the top end C model seem to be easier to come by.

Thanks again!

[ducatilover]

Thanks for that!!

Does anyone know if the 250C model block and head would fit the B model as I have seen one on ebay and the parts for the top end C model seem to be easier to come by.

Thanks again!

As far as I know they are the same, not sure about cams and valves though. They all have the same bore and stroke on A and C models, restricted C models are the same, thicker head gasket, softer cam profiles and possibly retarded timing?

Just a thought, have you checked the valve clearances? A minimal clearance may cause low compression.
If it's bent valves, you should be able to hear them.
Do the leak down and compression tests yourself, just so you know what's going on, don't go on the other guys word.

Good luck dude, let us know how it gets on.

[ZXCharlieR]

As far as I know they are the same, not sure about cams and valves though. They all have the same bore and stroke on A and C models, restricted C models are the same, thicker head gasket, softer cam profiles and possibly retarded timing?

Just a thought, have you checked the valve clearances? A minimal clearance may cause low compression.
If it's bent valves, you should be able to hear them.
Do the leak down and compression tests yourself, just so you know what's going on, don't go on the other guys word.

Good luck dude, let us know how it gets on.

Hi DucatiLover,

Thanks again for taking the time to answer, one thing I have been told by kawasaki here is that my model is 48mm bore and the C model is 49mm bore, for some obscure reason????

I have the opportunity to buy a block for £70 with the 49mm pistons so that's why I am asking, if it's rings then I have to take 49mm rings and reduce them to 48mm, that, I do NOT feel like doing.

So you can see the dilemma I have, or go with the bigger bore head and have more access to parts or stick with the one I have and see if I can get a batch of rings done.

Cheers again!

Charlie

[ducatilover]

Hi DucatiLover,

Thanks again for taking the time to answer, one thing I have been told by kawasaki here is that my model is 48mm bore and the C model is 49mm bore, for some obscure reason????

I have the opportunity to buy a block for £70 with the 49mm pistons so that's why I am asking, if it's rings then I have to take 49mm rings and reduce them to 48mm, that, I do NOT feel like doing.

So you can see the dilemma I have, or go with the bigger bore head and have more access to parts or stick with the one I have and see if I can get a batch of rings done.

Cheers again!

Charlie

Yours is the B model isn't it? I don't think I've ever seen one here.
Try going through some worskshop manuals as I really do not believe they have a different bore.
If you narrow the problems down to valves (I think very unlikely) I'd try find B model parts if they are different (I do not believe they would be at all)
If it is rings (More likely) you should be able to get the right ones from Kawasaki.
If it's a headgasket (Most likely) then it's in comparison an easy job.
Just make sure you know exactly what is wrong with it.

If you're very unlucky it may have a cracked block, but, I haven't heard of one doing that yet.

[ZXCharlieR]

Yours is the B model isn't it? I don't think I've ever seen one here.
Try going through some worskshop manuals as I really do not believe they have a different bore.
If you narrow the problems down to valves (I think very unlikely) I'd try find B model parts if they are different (I do not believe they would be at all)
If it is rings (More likely) you should be able to get the right ones from Kawasaki.
If it's a headgasket (Most likely) then it's in comparison an easy job.
Just make sure you know exactly what is wrong with it.

If you're very unlucky it may have a cracked block, but, I haven't heard of one doing that yet.

Hi DucatiLover,

Thanks again for the help, I have located a block with pistons so if it is the block then at least I have a C model block to put on it, just wondered if the C block would be compatible, I'm sure there's not that much difference between the 2, if any.

I think the B model e=is even more rare than the A model, I haven't seen any on the market before now and yes, the bore is 48mm but according to Kawasaki here, the head gasket is the same so I suppose the block is the same but with a 49mm bore and pistons.

I will have a look and do a full leak down test next week when I have a bit of time, the good thing is I have a good mate who has a leak down tester and he'll have a quick look at it for me, thank god!!!

I will post a full progress and let you all know how I get on, I am actually hoping it's just the head gasket as it would be as you say, in comparison, an easy job, just did one on my Saab last week.

Just a quick question, someone on here was selling a ZXR250A that he was trying to turn into a turbo, that is something I have never seen, does anyone have any info on that at all? I would love to be the only ZXR250 Turbo owner in the UK, I think that would be more like a 2Stroke 250 then, loads of power and lots and lots of fun!!!

Thanks again, you are a gent!

Charlie!

[ducatilover]

Hi mate, the B and D models are very hard to come by. There were a handful of "SP" B and D models made, they had a different CDI unit and altered 1st and 3rd gear ratios, one or two of them had single seat units.

There is naff all info around on the B/D models sadly.
I would hope the C block would work, I myself would just replace it with a complete C model engine, would be easier than making a hybrid B/C.

If you can find a small enough turbo you could do it. I had a set of headers + and intercooler I made for a VT250 Spada and it was to use a CT12A turbo from a JZZ30 Toyota Soarer. The oil feed lines to the turbo is easy, you run an adapter from the oil pressure switch to the turbo and a return to the sump. Jetting the carbs would be an interesting problem, but, easily do-able. I'd love to have finished the VT turbo, but, I imagine it would have exploded pretty quick.
Making an intercooler is easy, I cut down a Nissan Skyline GTS-T intercooler, cost me nothing.

It's certainly do-able if you have the time and money, you wouldn't want to run much boost through it though, 4psi i would say. I think a good two stroke would still outrun it, but it'd be uber cool.