Low Compression = Pi**ed Off

[z1000puddin]

Just put all me bits back together...

Barrels 903 bored out to 1015 wiseco - Measured @1/2" Thou out of oval on all 4 barrels,measured 20mm down from top,& bottom of liner & centre of liners
All pots were bored to suit each piston all 69.97mm to 69.99mm

Ring end gaps were slightly over at 5 to 6thou

New gaskets- base & head

Valves all reground/lapped in & seats recut.

Clearance - Ex 5-6 thou In 2 1/2 thou to 3 1/2 Thou

Took the bike out on Sat & Sunday & put in around 100 miles at varying steady revs.

On Sunday,When first started, I notice it was still smoking more grey/not quite black in colour.
Took it out again to see if it would clear,ran quite well & pulled quite good (got annoyed & redlined it in 1st,2nd & 3rd before I thought about totally knackering the engine.

Back to the house and whipped out the plugs - sooty but not wet black, All showing signs of rich mixture (Which I knew & hopefully have this sorted on Friday)

While hot I did a compression test (wide open throttle)
#1 - 105psi
#2 - 100psi
#3 - 110psi
#4 - 110psi
Now only 2 months ago and only 3-400 miles ago I checked the compression and it was
#1- 130psi
#2 -125psi
#3 -135psi
#4 -135psi

My Question is after all this rambling ....
Would my very rich fuel problem,cause premature wearing of the rings ??Through petrol wash ??
On a couple of occasions I had to limp home on 3 cylinders,due to plugs sooting up.
Carbs have 20 pilot & 120 main (These may have to go down to 117,5) I am not sure what clip position.

I have arranged to have the 28mm carbs (late 1974 circa) set up by Highland Dynos on Friday.
I will also get a leakdown test done,to see if this will pinpoint the problem of low compression.
I have ordered new wiesco rings from z1Enterprise (just in case).

Any pointers would be greatly appreciated.....

stu

It is really pissing me off now,as I am fed up with this "Chuffing Train"

[z1bman]

hi have you put synthetic oil in the motor?

[z1000puddin]

Z1bman - No good old Castrol 10w40 (Asda was doing a deal a while ago)
I got 40 litres in me garage & at this rate I may well use it all up !!

stu

[z1bman]

is it burning oil?

[z1000puddin]

Hard to say exactly as I have a couple of small leaks (a couple from the crappy alloy end caps & small leak from inner sprocket casing)
The smoke seems to be ,I think more fuel than oil, As it seems more grey/black than white/blue

stu

[z1bman]

if the compression is low either valve timing. but would be much lower than what you have got or piston ring or rings including oil ring broken or not bedded in properly ?

[z1000puddin]

Rings was my first thought,that why I ordered a new set.

I would have thought that 100 miles would be enough to bed in though ??

Would you say my ring end gap is too large ??

I would think a broken ring would show a bigger drop of compression to that particular pot .

I double checked that the oil rings were correctly "butted" & Not over lapped.

As the 903 liners are bored out to the MAX and very little taper... I fitted the pistons to the barrels first and then to the rods.



stu

[Big Fluff]

When liners are bored out to their MAX size, if the engine gets too hot, it is quite common for them to go slightly oval after a short while, resulting in exactly what your are experiencing.
I would NEVER promote boring liners to the max size.
Been there, seen it, had it, not good, but hope this isn't your problem.
Regards, Will.

[Mark Tiller]

the A1/2 barrels are best to work with if a capacity increase is the target

[z1bman]

i think you should invest in a z1000 cylinder there is a set on e bay at the moment. your ring gap is slightly over the minimum limit but i wouldn't say this is causing your low compression . most likely broken rings ?

http://www.ebay.co.uk/itm/140595377939? ... 500wt_1156

[Rich]

repeat your compression test, then put a squirt of oil in the bores and do it again, if it increases dramatically it's the bores/rings. if not the valves. have you rechecked the valve clearances since it has settled down?

[z1000puddin]

Rich,
I did try the teaspoon of oil in the bores,the compression came up only marginally - Up by around 5 psi per pot

You may have put yer finger on it-- No I havent rechecked the valve clearance.

I have the bike booked in tomorrow for a leak down test & carbs to be set up.

Will let ya know how I get on.

Z1bman
Maybe an easier solution with the thou barrels (At least it will be easier to fit the bloody rings)

Cheers for your advice

Stu

[DogsbolloxofZ1B]

Have you had the head & barrels skimmed? If so make sure the two collars that locate the head to barrels aren't bottomed-out and not allowing full compression of the gasket & 'O' ring. ie if you've skimmed 0.5mm off the head and 0.25 off the barrels then reduce the collars by 0.75mm

Doesn't fully explain the earlier high readings but worth a check..

Mike

[zkeith]

Rich,
I did try the teaspoon of oil in the bores,the compression came up only marginally - Up by around 5 psi per pot

You may have put yer finger on it-- No I havent rechecked the valve clearance.

I have the bike booked in tomorrow for a leak down test & carbs to be set up.

Will let ya know how I get on.

Z1bman
Maybe an easier solution with the thou barrels (At least it will be easier to fit the bloody rings)
have you put rings on upsidedown top two rings.take exhaust off check for oil in exhaust ports if you have a broken tab on oil control port will have oil in. are valve
guides good also stem seals . if all ok wisecos can take 5-700MILES to run in and the bike can run like shit and eat plugs for the first 2-300 miles
Stu

[Rich]

Check the valves tonight then - it'll save you time (£££) tomorrow. If you have had the stems ground to get back into shim range also check that they are at 90'. If at an angle the clearance will change as the valve rotates.