Struggle to start after top end rebuild

[Astandane]

Ok guys, as I'm sure you can tell from the title, I'm struggling to start my GPZ400 (ZX400 1986) after a top end rebuild.

Here is a list of work done:

Piston rings replaced; no work done to bores as ok and budget restraint.
New valve springs, seals and lapped in.
All relevant gaskets and O-rings replaced.
New header pipes to replace rusty old ones.

I've done everything by the manual (Haynes) here; 1000x checked the timing to make sure it's correct and fitted everything as described. Valve clearance ok.

With a fresh battery, the engine will turn over just fine. But there's no 'go'. It's almost there but is just missing something which I can't pin down.

Before the work compression was 125, 125, 110 and 145. Admittedly all cylinders are now only at 90, though this is perfectly consistent across all four. It's been suggested that this is just because of the new rings/old bores, and should still start. I have adjusted the timing since then as it was slightly off by a chain pin but haven't been able to check compression since as it was a borrowed tool form work.

Sparks are nice and blue on crank; gap is correct.

Fuel is flowing to all carburettors which were totally stripped cleaned within the last year.

Ignition coils, leads and spark caps are new. Old plugs but new ones coming in post.

I'm totally out of options here; I've tried spraying other things into the inlet to try and kick start the bike (without flooding everything). It want's to go as I said, and when turning over just keeps getting there but not quite.

Seriously desperate for help!

Jon.

-Edit-

Video links for any interested parties:

https://youtu.be/Ud2JnBUOPGA
https://youtu.be/XNSG9XZVv8k
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Kymco Pulsar 125 Suzuki GN 125 Kawasaki ZX400 Honda CBR400RR NC23

[chris-red]

Why did you bother with half a rebuild with those compression results?
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[Suntan Sid]

Those compression figures are low, an absolute bare minimum should be 100psi.
What does the manual say is a good compression reading?
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"Everybody needs money, that's why they call it money!"

[chris-red]

[Suntan Sid]

[chris-red]

[Suntan Sid]

OP, might be worth doing this test mentioned on this website:-

https://www.dansmc.com/compression_test.htm

[VultureZ1300]

Hi did you hone the bores before fitting the new rings? Might explain low readings as new rings won't work on smooth bores,probably smoke as well if you get it running.
Cheers. Vulture

[Robby]

By the sound of the description the low compression test results were taken when the timing was out by a tooth.

Now to be honest, it sounds like your ambition exceeds your ability, so diagnosis will be a bit vague seeing as we have to make allowances for mistakes made during the rebuild.

You have fuel to the carbs, you have a spark. You probably have enough compression to fire. This would suggest that the failure to start is to do with timing or a big mixture problem.

So, things to check:
1. Timing. Is it really right? It could be out by a tooth, or by 180 degrees.
2. Ignition timing. Have you mixed up the HT leads (putting ignition timing out by 90 degrees).
3. Fuel. You know its getting to the carbs. Have you messed with them? Are the inlet rubbers in good condition and firmly fitted. If they are loose or split, the air leak will cause trouble. Maybe you removed the covers on the balancing ports during the rebuild and haven't refitted them.

[.Chris.]

Assuming yours is the ZX400C2 model, my Haynes manual says compression should be 109-171psi when the engine is hot, with no more than ~15psi difference between cylinders.

Check that you've got the plug leads back on in the right order. Given that 110psi is considered acceptable, I would have thought that the engine would at least run with 90psi compression, provided nothing else is amiss.

Or, sell the bike to me for pennies
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Chris
1985 Kawasaki Z550F

[MaybeGuy]

Idiots like this are the reason lots of bikes die.

Lots of stuff can be done to confirm shitty rings that don't involve taking the engine apart. You can't just assume "rings" when there are so many variables, but as you've already done it:

Ring gaps? You probably don't know.

compression test with oil? probably not tried.

Piston to bore clearance?


Did you measure the bores before buying the rings? or did you just buy a "ring kit bruv, make ur bike fully sik & hektik".

My prediction is you've bought the wrong rings, and have a massive ring gap.
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Blue_SV650S wrote: it was a sh1te wheelie, but it proves that he can get it up in 3rd and can do angles. In summery, mattsprattuk is a gobby little sh1tebag, dopehead tw4t, but sadly for all of us, he probably isn't THAT full of sh1te!!
Kickstart wrote: Hi I tend to agree with Matt. All the best Keith

[.Chris.]

Just a thought - you have turned the fuel tap to the 'prime' position, haven't you? The vacuum tap won't supply fuel in the 'on' position unless the engine is running.

What was the reason for the engine work? Was the bike not running properly before?
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Chris
1985 Kawasaki Z550F

[Ariel Badger]

A squirt of oil down each plug hole will raise your CR.
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Bikers make great organ donors, get 115 on your licence today.

[Vincent]

As OP mentioned, the old bores/new rings can explain the compression readings and I wouldn't worry too much, it should still start.

My advice would be to grab your biggest mate and try a couple of really good bump-starts. I don't know why but I've found rebuilt engines can take a lot of spinning to fire up again and are more likely to do so when bump starting. If that doesn't get it going, something has to be wrong.
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Space Is Deep

[Astandane]

Ok well to clarify a few raised eyebrows; the reason for the rebuild was due to a total lack of top end power. The bike would struggle to get past 70 on a windy day.

Upon examination this was probably due to the valve springs which were way out of their service limit. However, the cylinder base gasket was also leaking and this was seen as an opportunity to replace the rings anyway.

Bump starting hasn't worked after repeated attempts, and oil down the bores has not affected the compression.

The fuel is definitely reaching carbs and cylinders.

The rings are not incorrect.

Everything is connected properly as I took both photos and have the manual with relevant wiring diagrams. I am however dubious about it's description of setting the cam timing:

Reason being is that, despite following it's instruction in counting chain pins, I cannot get the cam timing marks to line up as described. The difference is not massive, but the inlet is not parallel to the cylinder head. It's been suggested that moving the cam one tooth forward would resolve this, however this obviously goes against the described procedure. Yet, again, the timing marks are not exact as they should be. Advice?

I admit that this is generally new to me but I've followed everything as described in the manual, and I know the bike well enough to replace things such as pipes and what not in the correct place.

Main concern at the moment is getting the timing marks lined up. As I said, I just can't seem to achieve this by following the manual. It described setting the exhaust mark to be between two LINKS, using the pin immediately above it as '1', and then counting back to 43 and 44. IN mark should be between these, but does not lie parallel.

Sorry for the late reply by the way!
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Kymco Pulsar 125 Suzuki GN 125 Kawasaki ZX400 Honda CBR400RR NC23

[Ariel Badger]

You have sparks but are they in the right place? my betting is your ignition timing is way out for some reason.
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Bikers make great organ donors, get 115 on your licence today.

[Polarbear]

Photos of timing marks when in the lined up position please.
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Triumph Trophy Launch Edition

[Piercee100]

I had the same symptoms on an engine where I failed to spot a tiny nick on an exhaust valve stem. It was a single cylinder scooter though. Have you checked all the valves have been installed correctly?
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Rides: Honda H100a (Retired), VT500e (Sold), Kawasaki ZX400 (sold), Kawasaki GT550 (Sold), Suzuki Inazuma (Daily), Honda CD185t (Broken), LML Star 2t (Last run edition).

[iooi]

[bladerunner]

Was wondering if 180 degrees out after he said oil in the bores made no difference to the low CR. I had a Haynes book of lies that did that if you were daft enough to follow the pic's. Or your valve clearances are to tight
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Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's

[Astandane]

Hi guys and thanks again for all the replies.

I'm not going to post pictures as I've managed to sort the timing out, but of course I will detail how this was done.

When taking the engine apart the manual says to turn the crank so that that the '1.4 T' mark is aligned with the crank index mark; this puts the cam shafts in a position so that their alignment marks face outwards with pistons 1&4 at TDC. If you were to rotate the crank again to this position, the alignment marks would point inwards.

It was suggested here and at work that the timing was 180 degrees out. I rotated the crank to the timing mark so that the cam markers pointed inwards, and then removed and reinstalled so that they pointed outwards as is necessary.

The timing marks lined up properly first time, as opposed to before when it seemed impossible.

I'm letting the gasket sealant set overnight before I do any more so I will update tomorrow
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Kymco Pulsar 125 Suzuki GN 125 Kawasaki ZX400 Honda CBR400RR NC23

[A100man]

It's now tomorrow - what you got ?!
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Now: A100, GT250A, XJ598, FZ750

Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600

[Astandane]

Unfortunately just a minor set back; the starter motor clutch has gone. Every time it gets load from the engine it slips. But eBay to the rescue! I guess after 30 years and the recent hard starting, it was about time.
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Kymco Pulsar 125 Suzuki GN 125 Kawasaki ZX400 Honda CBR400RR NC23

[Ariel Badger]

Bump it.
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Bikers make great organ donors, get 115 on your licence today.

[Astandane]

Bike has always been hard to bump, not something I need from a daily ride.

https://youtu.be/BBsIZ89sUrY

I need to know if this is the starter clutch; last thing I need but engine won't turn over via the starter now.
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Kymco Pulsar 125 Suzuki GN 125 Kawasaki ZX400 Honda CBR400RR NC23