cyl head pressure

[FBJ]

Hi all, the Mrs has a 1100 kat, it's uses a fair bit of oil and smells and smokes a fair bit, not whilst cruising when you pull up after cruising at 80 for 20 miles it will smoke a fair bit. During a run around Europe last year it used 4 litres in 2200 miles.
Anyway got a good head of Scottie (Katanamangler) cheers bud, before trying to fit it I carried out a compression test to try to estabish if the problem is head or bore, I warmed the engine fist held the throttle open fully and cranked witha fully charged battery, got these resulfs, no1 = 115psi, no2 = 85psi,no3 = 60psi and no4 = 160psi. So I then squirted 3 squirts from my oil can into each cylinder and got the following no1 = 140psi, no2 = 120psi, no3 = 100psi and no4 = 160. The manual says that the cylinder pressure should be between 128 and 171 psi (a variance of upto 28psi). No4 shows no change, no 1, 2 & 3 all have a little change but all are still below the minimum 128psi. What are your thoughts? head or rings?
Thanks FBJ ::) ;D

[Russbusa]

I doubt if a cylinder head problem would cause the differences in pressures that squirting oil in the bore would make.

I'd go for the rings / bores / pistons with this one, either way it has to come apart so it would make sense to remove the cylinders.

[john boy]

have to agree with russ sounds like rings worn or bore wear
extra oil giving better seal i.e better compression

[Katgeezer]

That no3 pressure is well low John and no2 isn't much better, the improvement with your oil squirt definitely says rings to me.

[FBJ]

Think I made a boo boo, had someone turn up to visit half way through the compression test yesterday. anyway I forgot to hold the throttle open on all tests. gutted, so did it again, much better, they are higher than the manual says ie max is 171psi, when warm these are 165, 175, 165, 170 when wet 195, 195, 190, 195. so the head has obviously been skimmed, this is a quick kat. so the compression looks ok. I'm really hopeful after getting accurate results that the problem is the dredded crack between the valves, getting worse when hot.
Your thoughts?
Thanks

[FBJ]

I'm confused, the reading taken when hot shows that the motor is healthy, however when I added the oil the reading changes indicating that the rings are worn, so how can the motor be healthy?

[johnr]

what coils you running? my 1170 used half a litre every 500 miles, valve stem seals needed doing.

not sure if the crack from plug to valve seat is gonna make it smaoke. look logically at it, hows smoke going to get into the combustion chamber? past the rings, down the valve stems and thats pretty much it. even if it could get through a crack in the head are you so sure it would suck oil in or would it not be more likely to blow exhaust gasses out?
when you say it gets worse when hot, do you mean it runs bad or just smokes more?

[johnr]

when you put oil in the bore, then you decrease the volume in there by whatever amount of oil you add, thus the volume of gasses has to be compressed into a smaller area and the compression rises.

[FBJ]

Some info, what a shat day
Right after testing the Mrs bike I couldn't get my head round the difference when wet and when dry, this was before I just read your response (mustavadump). So I decided to check the compression on my Kat as it's a 1170 aswell, I know it's healthy and uses little to no oil. Roger Upperton sorted the rebore 1170 kit and gapped the rings about 4000 miles ago. Anyway the good news is the difference between wet and dry is better on the wifes than mine, so it's pointing at her cyl head. Really really bad news is that one of my cylinders only has 60psi, gutted I had no idea, no only hint being a bit lumpy at idle. Being the patient guy I am I just ripped it to bits, rocker cover of hoping it was a tight valve, it's not. So removed stock carbs, air box, exhaust and pulled of the head, turned it upside down and filled each chamber with petrol. none of them leaked quickly, however the first one to drain was the one with the lowest compression, I guess under pressure it would leak quicker, so hopefully it's just the valve seats, I removed the barrels to check a ring wasn't bust, no probs there, all mint.
Reckon I might send the head to Roger Upperton to sort the head out. Anyone got any idea of cost?
A gutted FBJ

[johnr]

if its just the valve seats, why not try lapping them in and seeing what difference it makes. cost you nowt but time then!