1997 Rebuild gone bad

[quarterback]

Ladies and Gentlemen of the org - Hello, I'm new here!

I bought a 1997 firestorm with 47k miles on it in October 2017 as a bit of a project. Previous owner thought that it had the usual CCT failure (which it did).

Since then I have:
* Fitted new valve guides to affected valves
* Fitted new valve stem seals to all valves
* Replaced damaged valves
* De-coked heads and pistons
* Replaced cylinder head gaskets
* Stripped, cleaned and rebuilt carbs as per guide on this site
* Re-timed as per guide on this site
* Re-timed (again)
* Re-shimmed valves - compression was almost non existent - reshimming improved this, but isn't spot on yet.
* Re-timed

This brings us to where I was last night, which is that I have approx 90psi compression in both cylinders, which isn't enough. This reading was taken with the engine cold. No airbox on and no tank on. Filled carb bowls by squirting fuel down the two feed hoses until they backed up. Bike was turning over (I think too slowly personally - based on start up videos from youtube) and not starting, but was drawing fuel. There was fumes coming from the valve cover breather hoses (as they are currently not connected to anything) though these fumes did not smell of petrol...so not sure if it's just oil vapour or something?

The cylinders and heads have been fluid tested and do not appear to have any leaks and the piston rings seem to be liquid-tight.

I believe that the compression may not be high enough as the engine isn't turning fast enough to produce that compression (is on a brand new motobatt AGM battery - fully charged), however, would expect that it would still kick as if it was trying to start.

Have also confirmed that there is a spark to both cylinders.

To recap, all rebuilding has been done as per guides on this site, so I've reached a bit of a dead end here. Does anyone have any wisdom they wish to impart?

Cheers

Craig

[Chris58]

I would do a leak down test if you have the guages / regulator for it.

set the regulator to 100psi with ball valve on output hose closed, making sure there are no air leaks in the hoses etc.

With the cylinder at TDC, apply the 100psi(aka 100%) at the spark plug hole. Make sure you have a very good hold of the flywheel with a johnson bar exactly at TDC, there is the potential that the pressure will push the piston down with great force.
You can measure the leakdown percentage this way... any more than 10% Is getting to be too much, les than 5% is very good

you can see where your losing compression by using a stethoscope (or your ears) with an open ended tube on it to listen in the Intake, exhaust, and oil cap.

Its normal to hear some hissing in the oil cap because the rings usually do let a small amount by.. but nothing should be heard through the valves

[KermitLeFrog]

May be electrical. Try bypassing the starter solonoid. Power the starter motor directly. They should turn over fairly quickly.

[quarterback]

Thanks for above folks.

Tried the old oil in the bores trick tonight....immediately compression climbed to 155psi on both cylinders.....guess I need me a set of rings then!

[tony.mon]

Certainly looks that way.
Engune turning over slowly is usually a poor main (long) power lead going from the starter solenoid to the starter motor.
Try bridging it with a piece of 30 amp cooker lead connected in parallel with the existing lead, if it turns over quicker you need to repair or replace it.
The other alternative is the lower end connector wher the lead joins the starter motor, they corrode easily.

[Chris58]

Thanks for above folks.

Tried the old oil in the bores trick tonight....immediately compression climbed to 155psi on both cylinders.....guess I need me a set of rings then!

sounds about right. sorry to hear it will have to come apart again

[sirch345]

It seems a bit odd for the rings to be gone at 47K although of course you don't know the full history of the bike.

I would try (what has already been suggested) first making sure the starter is getting the full power from the battery,

Chris.

[AMCQ46]

although the compression has shot up with the oil in the bores, I wouldn't jump straight to taking it apart again and fitting new rings. Like Chris said, the mileage is not that high, so it might just be sticky or glazed rings.

sort the starter motor so it turns fast enough, get it running, do some heat cycles and then do the compression test again.

[quarterback]

Cheers folks, I will look in to that.

I did replace the terminal on the starter as part of the refurb...though admittedly only with an appropriately sized machine screw.

I'll see if I can get it going by jumping from starter relay to motor. When it was turning over, there was fumes coming out the valve cover breather...so suspect the rings are probably passing too much...but ya never know...

[sirch345]

I just had another thought

I don't suppose you have over filled the engine with oil by any chance
What level is it at

Chris.

[quarterback]

Nah - was low actually - had to top up to 1/2 before trying to start it.

Will inspect the rings I think as a starting point.

Cheers for the help so far folks!

[sirch345]

Nah - was low actually - had to top up to 1/2 before trying to start it.

Will inspect the rings I think as a starting point.

Cheers for the help so far folks!

Okay so we can rule that out. The bit I find hard to accept is the fact you got 90psi on both cylinders from the compression test before you added the oil. That still makes me question if the engine is spinning over fast enough. Any chance you could borrow or get your hands on another known good starter motor before stripping the engine down

As Al (AMCQ46) pointed out, the rings could be sticking in the piston grooves. That to me sound like a good possibility especially if the bike had been standing not started for a considerable length of time, even more so with each cylinders showing 90psi compression.

although the compression has shot up with the oil in the bores, I wouldn't jump straight to taking it apart again and fitting new rings. Like Chris said, the mileage is not that high, so it might just be sticky or glazed rings.

sort the starter motor so it turns fast enough, get it running, do some heat cycles and then do the compression test again.

Chris.

[quarterback]

Will see if I can beg/borrow a known good one and see if any difference. Will also try jumping battery direct to starter to rule out voltage drop over relay etc.

Exhaust fumes coming from the valve cover breathers is still a concern, but would be over the moon to find the rings are fine.

I'm off to the USA shortly so not going to have time to look at it for a couple of weeks. One of the lads has suggested filling the bores with a diesel/wd40 mix to see if it can unstick rings etc while I'm away.

Good idea in your opinion?

[sirch345]

Will see if I can beg/borrow a known good one and see if any difference. Will also try jumping battery direct to starter to rule out voltage drop over relay etc.

Exhaust fumes coming from the valve cover breathers is still a concern, but would be over the moon to find the rings are fine.

I'm off to the USA shortly so not going to have time to look at it for a couple of weeks. One of the lads has suggested filling the bores with a diesel/wd40 mix to see if it can unstick rings etc while I'm away.

Good idea in your opinion?

* Re-shimmed valves - compression was almost non existent - reshimming improved this, but isn't spot on yet.


Cheers

Craig

I've just been going over your original post again

Could it be possible the valve clearances were well out of spec's (clearances too small) when you re-shimmed them meaning the valves or some of them were not closing complete If that had happened (which you probably already know) may mean the valves and seats need a re-grind by hand to make them seal again. If it was the inlet valves that were re-shimmed you could remove the carbs and pour some petrol in the inlet ports to see if the valves are sealing or not. Just remember petrol is highly inflammable.

As for trying some releasing agent of some sort in the bores over a few days. If I was going to do that I would want to change the oil before starting the engine after doing that, also you want both piston away from TDC (part way down the bores).

Personally I would check out the other suggestions first, but it's your bike so it's up to you

Good luck with it whichever way you go,

Chris.

[Chris58]

Will see if I can beg/borrow a known good one and see if any difference. Will also try jumping battery direct to starter to rule out voltage drop over relay etc.

Exhaust fumes coming from the valve cover breathers is still a concern, but would be over the moon to find the rings are fine.

I'm off to the USA shortly so not going to have time to look at it for a couple of weeks. One of the lads has suggested filling the bores with a diesel/wd40 mix to see if it can unstick rings etc while I'm away.

Good idea in your opinion?

Fumes coming out the breathers definatly points to rings.
Not a bad idea in my opinion, not sure if you need to fill them right up though, and change the oil afterwards.

I would just put a few drops of oil in to get the compression up and get it running. It may be fine after that.