compression problemos

Okk, so i did a compression test today and got
#1- 60
#2- 65
#3- 59
#4- 62

I put some oil down them and it only brought them all to around 90, give or take a couple. Checked all the valve clearance and they're all in spec. Any ideas?

Also the engine was cold because i don't have the carbs on it. I also don't have the exhaust on it. Does that effect the numbers? I figured it would a little bit but not enough to drop my compression numbers all the way down like that.

thanks much

 

Step one: TRY A DIFFERENT GAUGE. Those numbers are all close enough to point to a faulty test rather than a problem with the motor.

Having the carbs and exhaust off won't affect the compression test results (other than the fact that they might actually be a tad higher with those components removed.)

 

Ohhh man, just bought the gauge from harbor freight today!

 

Could you walk us through the procedure on how you did the compression test? More precisely, did you turn the motor over with the starter or manually? How many compression strokes did you have on each cylinder to get those readings.

 

The Harbor Freight gauge I have came with three hoses to fit different plug sizes. The gauge itself has a hose on it. When it's assembled it makes a long piece of hose. It takes quite a few revolutions to pump all that up.

You should crank the engine until the gauge quits rising.

 

I first removed all the spark plugs, then I attached the compression gauge. Hooked the battery back up and used the starter. Put some oil in the holes and I cranked it until the gauge stopped moving. By the last cylinder the battery was pretty much dead.

 

Unplug your tci when you do the test! And you HAVE to have the throttle open 100%.

 

krs14 already took the carbs off

 

seems to me that 4 compression tests should not be hard for a battery at all with the plugs out.
i had a 60 and a 65 and they didn't come up .until i started it

 

im goin to try and disconnect the tic unit tomorrow and then redo the compression test, ill let you guys know how it goes!

 

TCI should ALWAYS be disconnected while performing a compression test otherwise it could get damaged.

 

Disconnecting the TCI is to prevent damage to it. It won't affect the results of a compression test.

 

since I don't have my Haynes manual in front of me
and the fact that I am planning on doing a compression
test in the next few days
where is the TCI and where do I disconnect it from?
thanks

 

Under the seat, pull the 2 connectors.

 

Under the seat, pull the 2 connectors.

 

If it's a Maxim, I think it's under the LH side cover.

 

Thanks Fitz
got the parts enough to replace the valve cover gasket
a new layer of gasket sealer
and new bolts
time to see if I have a parts bike or something viable
hoping for the later of course
but since I was super naughty and drove it the day after I got it
and it ran splended, even had it over 60mph
I am guessing it will be fine
has started fine every time I have had too

 

Ok so I unplugged my tci and put some oil down the holes, after a couple rounds on each, cranking till the gauge stopped, these are the readings I got:
#1- 100
#2- 105
#3- 92
#4- 101

Is this the enevitable rings change?

 

What model and year of XJ is this?

I think anything over 100 PSI would be OK, but cyl#3 is definitely low.

 

You wrote that you checked your valve clearances. Can you post your readings here. just to make sure?

 

It's an 86 xj700
Ex. In.
1. .17 .14
2. .19 .12
3. .20 .14
4. .19. .14

 

Readings are in spec, indeed. It is a bit odd that your cylinder with the widest clearance as the poorest compression.

 

LOL ya, i forgot you said that

 

The point of the oil is to rule out the rings. The proper way to test is dry first. Then if compression is low a small amount of oil and another test. If the compression comes up significantly it's a ring problem. If it doesn't come up then it's likely the head gasket or valves.

That all assumes a good strong battery and a decent gauge.

Assuming it is rings it's not likely to be just a ring change. Usually you need to bore and go to oversize pistons and rings. Tough parts to find and a big bill if you do.

If those numbers are accurate the best bet is a leak down test to see where the compression is going.

 

We could just have a rusty valve stem on #3. too.

Everything Carl said is exactly right. Don't pull it apart until fully diagnosed; you give up the ability to further analyze as soon as the head comes off.