Help or advice with this 1977 xs400 project's engine?

[dan warr]

Hi all, really need some help and advice with this 1977 xs400 project. In advance sorry about the essay, lol

Its a 1977 x400 kick-start (& electric start converted) and runs off points for the ignition timing.

Obtained the bike as a runner out of storage, but was coughing and running a bit poorly. Got it running a bit better and rode it on the road for about 3 or 4 months, until I had starting issues. It wouldn’t start again or did but had real trouble to get it going again once it got too warm after a few miles.

Decided to rebuild the engine.

Strip went fine, nothing in particular found except I found a slightly bent valve and replaced with a good’en. Now can’t get the engine to start?

1) Cam timing seems to be right, followed manual. Pointer on Alternator to LT, cam sprocket lines levelled to the head, with pointer arrow pointing up (where the bolt attaches the sprocket to the cam), and the little grub holes on the cam pointing up. So shouldn’t be 180 degrees out (which would cause it to not run)?
The lines aren’t exactly parallel but it’s the closest I can get it, its probably about 5 degrees or less off, tried shifting the sprocket about to see if jumping a tooth on the cam sprocket would bring it more parallel, but it takes it too far back the other way so its maybe 10 or 15 degrees off, so its as near to parallel as I can get it. Would this affect it that much that it wouldn’t run?

2) Setting up the valve timing next, rotated engine with thumb over spark plug hole to feel when the compression stroke is. Felt the build up of pressure on my thumb so waited for the nearest LT when rotating the alternator. Stopped at the LT and gapped the valve tappets on the left. Moved over to do the right side the same way, felt for compression with thumb on right spark plug hole, stopped at nearest RT once felt compression build up, gapped the valve tappets. Double checked it was the right stroke by taking off the inspection caps and watched the exhaust tappet/valve go down and up, and stopped at the nearest LT/RT(depending on side), checked tappets gap, all ok, and can be wriggled freely in the small valve/tappet gap. Meaning that there’s no pressure on the valves and they are all shut (cleaned and re-seated them in the rebuild so should be tight up).
Have I set the gap on the right stroke as with it being 4 stroke, that suggests at least two of the strokes would be upwards/compression strokes?

3) Points timing. Rotated engine till pointer on LF on the comp stroke (tested with thumb over hole) & gapped the points then, same for the right (RF) on relative stroke.
Mock test light made up and connected to left points string, and to + power source. As I rotate the engine round to compression stroke the light is off and as i reach the LF mark and go over the mark, the light stays off. Tried rotating the points base plate to see if i could get the light to come on but there was not enough adjustment, so I set it back to stock/default arrangement. Once continuing the engine rotation, the light comes on when it reaches RF/RT, and stays on until it reaches the next LF mark, and as it passes it, it then goes off. The inlet valve is then the next to open, is this right? Or is the cam 180 deg off? As I would expect spark to be delivered, which would ignite the fuel and then the next valve to open should be the exhaust so that the fumes can leave? Also I’ve been checking the comp stroke by testing with my thumb and watching the inlet tapped as the compression stroke comes after the inlet valve has been opened and then closed again?

4) Compression test. Bought a cheap compression tester on ebay and gave that a go. Results are low compression on left (25-65) and low compression on right (50- 75). Thought everything looked ok on the rebuild but obviously not as I’m led to believe xs400’s should achieve 100 -155 compression. Put a few squirts of oil in each side and both sides then reached 100 after a few kicks. Not fully clued up on compression testing but I’m led to believe that means valves are seated ok and piston rings are worn, as the oil seals around the piston, that’s if I’m testing it right. Test with only one of the plugs out at a time, and throttle open full?

5) Electrics & spark. Getting a good blue spark on each spark plug when earthed to engine head. Tested both coils and alternator wiring resistance as stated in manual, all tested ok or there about’s? (weather has been about -2 this week and only slightly warmer with the heater on in the garage, and the book suggests readings may vary with temperature and spec readings were taken at 20 degrees lol). Starter motor also fitted in the rebuild, could this affect anything, but wouldn’t think so as its getting a spark?
New condenser on so shouldn’t be that, would swapping the wires from the points make a difference or swapping the coils wiring over?

Tried kicking the bike over with easy start in but its till not having any of it. Not even a cough, puff, or splutter. Plugs just come out wet, think its a mixture of oil and easy start tho (from testing piston rings) but smells more of petrol.

Any input or help is much welcomed and would be greatly appreciated. Stuck on where to go from here. Is something I’ve done wrong, or is my next best bet wiring? Don’t think I can get the cam sprocket lined up any better but will find out after stripped to put new piston rings on.

Cheers Guy's

 

[drewpy]

did you try swapping around the orange and grey wires to the coils?

is your battery fully charged too?

compression seems way low, but was it with WOT?

 

[dan warr]

Hi drewpy, thanks for the quick reply.

No haven't tried swapping any wiring over yet, only tried putting the other coil lead from right side onto left plug. Bit of difference but not really sure if its right, still not even a cough or splutter tho.

Cant remember off the top of my head the wiring for the coils but will look into your suggestion as soon as i can, as have been called away on work training for the next week and a half so probably wont get a chance to look at bike till im back.

And yes battery is fully charged, had two on the go for when the other one had drained.

Yea compression seems very low, like i said, done the compression test and with a few squirts of oil in it shot straight up to 100! so thats pointing me towards the rings being f****d. Or Could it be worse than that such as barrel's or barrel sleeves worn? (also whats "WOT"?

Cheers

 

[drewpy]

Hi drewpy, thanks for the quick reply.

N

Yea compression seems very low, like i said, done the compression test and with a few squirts of oil in it shot straight up to 100! so thats pointing me towards the rings being f****d. Or Could it be worse than that such as barrel's or barrel sleeves worn? (also whats "WOT"?

Cheers

WOT = Wide Open Throttle

 

[dan warr]

Yes Think I tried it with both closed and open throttle but was still about the same reading?

 

[drewpy]

O dear, I think you need to check the bore for wear

 

[Scorpio1963]

Low compression could not always be piston wear,it can come from excess carbon on the valves.Where the maybe seating but not enough leading to compression loss.

 

[bcware]

The lines aren’t exactly parallel but it’s the closest I can get it, its probably about 5 degrees or less off

This is normal.


Did you remove the piston rings during your rebuild previously?

Did you wet compression test the bike while it was on its side stand? Center stand? I'd try it again and rock the bike side to side after you add the oil but before you kick it over to spread the oil completely around the piston. Perhaps you can achieve a higher reading; 100 wet is very low and less conclusive than I'd like to see.

What kind of oil is in the motorcycle and how much?

In regard to timing; I check the stroke by using a flash light. I can see the valves open with a bright light shined in the spark plug hole. On the exhaust stroke the exhaust valve will be open (visible). On the compression stroke both the intake and exhaust valves will be closed (not visible) and yes, this occurs just after the intake valve opens and closes.

I have received false readings from my compression tester before. Make sure the fitting is tight and the hose is not bent at an extreme angle. Perhaps try some oil around the provided o-ring?

How many time are you kicking the bike over for a compression test on each side?

 

[dan warr]

Thanks for the replys
Seated the valves in and cleaned them up when stripped engine.
But no didn't take rings off piston or check clearances or measurements on the barrels.
Will check when I get head off.

Bike was on centre stand whilst doing comp test, kicked it probably 3-4 times before checking comp reading, then re-setting and trying again.
Compression tester hose could have been bent round a bit so will cable tie it up from handlebars to keep hose straight, and add a few drops of oil around the seals.

Thanks for the clarification on the timing and what should be happening on what stroke
Will let you know what I find when I get chance to have play

 

[bcware]

Kick it over more. Do it ten or twelve times per side. Seriously! Sometimes this is what it takes to get a true reading. And yes, the throttle should be open all the way.

 

[dan warr]

Hi guy's,

Had a chance to have a play with the bike this weekend. But just came away more confused? :S

Tried the comp test again but kicking it more times, as suggested by 'bcware' (12+ times)
Dry test got 25-50, but with a few squirts of oil wet comp test achieved 125ish on both sides. Which points again to the piston rings, or the barrels :S
will have to wait till next weekend tho to get the top end apart and check the tolerances properly.

Got new carb inlet rubbers fitted.
Also while I was at it though I mite strip the carbs again, as acquired another set which though i could put the best of both together on one set.

Stripped and cleaned the carbs with carb cleaner, then paint thinners, then heard about boiling them in lemon juice, so decided to give that a try.
Carbs came up really well had a bit of dirt floating about and now look really clean and tidy, with all holes ad crevices clear as anything.
Next time you do a carb strip, try it, really recommend!!!
Set the carbs up to books specs, float to 31mm, idle (pilot) needle screws 2 turns out for a start (one of the needles bit worn but not bad)

Tried the bike again. No luck. just doesnt want to go!!!
Only get a bit of a back fire every now and then with a bit of easy start?

At least that's eliminated the carbs tho and i shouldn't have to touch them again, unless its to adjust idle (pilot)screws.

Swapped the coil orange and grey wires to the coil as suggested before, doesnt seem to make a difference?

This then brings me back to the timing? It should at least give me a bit more love than a pop every now and then, or run sh##ty if anything?

Thought i had the timing set up bob on as checked it many times, but that's the only card I have left to play as I'm stuck where else to go from here?????

Any help or suggestions is greatly appreciated peeps!

 

[16VGTIDave]

You already have the answer. Denying it won't change anything. The compression is way too low. You can try pouring cleaners into the cylinders to see if the rings are stuck with carbon, but I doubt it will work. You should be thinking about tearing down the top of the engine.

You can keep on trying other solutions, but until you get the compression up it won't run. It is you time and $, proceed as you wish...

 

[dan warr]

Rite peeps.

Got a few spare hours this morning so had a bit of a go with top end strip.
Complete top end off, both pistons out and the barrels on the bench.

At first glance I cant really see anything wrong with the barrels or pistons, the pistons slip nicely into the barrels and you can feel some resistance when sliding the piston up the barrels. No cracks anywhere or signs of bad wear, so time to take some measurements.!!

Repeating directly from the haynes book:

Piston/cylinder clearance, should be 0.030-0.050mm
can get 0.40 guage in on RH side, and 0.50 guage on LH side

Cylinder boar diameter, should be 69.0mm (+0.02mm)
got a reading of about that on both cylinders (top and bottom), tested with an old vernier caliper, but im not too good on reading the old ones, so am going to have to get a digital one tomorrow after work so as to double check specifically since the tolerance is only 0.02mm.

Checked the rings for gappage, did this by sliding the rings individually into the appropriate barrel.
Top ring end gap should be 0.15-0.35mm
got 0.55 on RH side, and 0.60 on LH side
2nd ring end gap should be 0.15-0.35mm
got 0.50 on both sides
oil rings should be 0.2-0.9mm
RH 0.8mm, LH 0.85, so within spec

ring side clearances also checked and all within speck.

checked the piston diameter aswell,
68ish mm top of piston (just above piston rings)
69ish mm bottom of piston.

There seems to be a small taper between the top of the bottom of the pistons, to where the oil piston rings start. Is this right, or has it been worn this way?

Results show then that either the top two rings are worn as they are out of spec, or.....
the boar of the cylinders could be out slightly, which as i tested the ring end gap with the rings in the barrels, would make the gap bigger.
Wont know for certain until get a proper accurate reading on the cylinders from new vernier.
Im hoping for a nice simple piston ring job for both, but well have to see.

Also I've heard something about 'Honing' the barrels when getting new piston rings in or something?? whats all this about then ??????

 

[dan warr]

Hopefully if i've done this right you should have some pics to look at now aswell

pic 1 shows RH piston/cylinder gap
pic 3 shows LH cylinder, top a bit mucky but only dirt and where the heats marked the top of the piston stroke. No visible step which would be an easy indication of barrel ware.

 

[dan warr]

few more

 

[rodeo]

what was the ring gap? I just did a quick hone and put new rings on, my gap was about .013 i think.

 

[dan warr]

Depends which gap you mean? Ring end gap should be 0.15-0.35mm(mine measured 0.50, 0.55 &0.60.
Or if you mean piston/cylinder clearance (as in my pic 1 on first lot of pics) then that should be 0.030-0.050 ( but think mine was 0.40 & 0.50 which is well out?)

 

[dan warr]

Also how did you hone your barrels if I may ask?

 

[rodeo]

Bought a flex hone; about 28$ on ebay,

Keep it nice and oiled and run it back and fourth in each cylinder fairly quickly at a medium RPM, breaks the varnish and gives the metal a nice cross-hatch pattern without increasing the bore diameter; just don't do it for too long.=D

 

[Scorpio1963]

You got the right one and its what I recodmend to people to use.After being an automechanic for years I used those alot.