Hi all, stumbled across a zxr c model engine today while helping an elderly widow de-clutter her garage & shed, the motor looks quite clean, has oil in it but no carbs or starter, and care has been taken to carefully seal all openings which indicates its a runner, theres no other bike parts lying around & nothing is known about the motor as he passed a decade ago. I have only ever compression tested a fully warmed up bike with a starter motor. Questions- can I turn the motor by hand to get a compression reading?, does the speed of the turn affect psi?, what psi should I expect by cold hand cranking if standard is 140-220psi?, could I use a drill to crank it faster etc? Things like this keep me awake all night, thanks in advance John
A decent size quality drill in lowest gear with a socket onto the stator may yield a result, or it may tear itself out of your hands. I wouldn't spin it for too long in any case as it's like putting in long decking bolts with a normal drill (the impact driver battery had gone flat), it will get very hot, very quickly... A decent size air drill, ratchet or impact driver however can't run too slowly and overheat - if you have access to air tools... I notice you've already got ZXR in your profile, what about swapping the starter motor in?
I'm with Ruckus on this one...I wouldn't try to force it. Maybe swap your starter motor onto that engine and try it with power. No carbs means your cold test will give high results or zero depending on what's going on in there. I remember testing a ZXR250C motor cold and with no carbs and getting 200psi+ readings. When I had it all together the cold readings dropped to 160-170psi. On a brighter note, let me know if you want to sell the engine.
I'd let @Murdo or one of the other more senior forum members make a suggestion before doing anything. Friction is your enemy and spinning an unknown engine to check its compression may damage it. I'd pull it apart and then decide what you want to do. No offence Linkin.
At least try to turn it over 720° with a socket and ratchet first (spark plug's out). If it turn's freely then i'd try with a power drill
If it's been sitting a long time as well you'll want to put some oil down the carb throats or down the spark plug threads. As Frankster said, friction is bad mkaaay
If it has been sitting for a long time, then there's every likelihood that the piston rings will be "stuck" in place and even a successful compression test will return inaccurate readings. Sorry to bang on about this guys, but I've become very "by the book" about engines in the last 12 months. I think I'll change my forum motto to "you can do it fast or you can do it right".
Haha, my 67 XR Fairmont sit's in the shed for up to 5 year's at a time and i just register it for 3 month's, put in a new battery and fire it up and off we go till rego run's out then it goes back into the shed till next time i have some spare cash Engine has only done under 7,000 mile's since being rebuilt in 1992, doesn't use oil or anything Adding oil down the carb's will increase the compression reading too
I agree, your readings will indicate that you've either got something or nothing. BTW with fresh oil, plugs removed and a decent drill of whatever persuasion you could turn the motor cold for a while to circulate oil to where it's needed before doing the compression test. It' difficult to know how much the rotation speed will truly influence the results, however with bearing surfaces at least lubricated it should turn at a decent clip to get a reading
Thanks Ruckus, I suppose that's what I was trying to say. My67XR's post about his XR makes a good point and in the end as long as there's plenty of oil in the right places to stop friction damage, then you should be okay.
Thanks for the feedback, I do have some time with this as the motor is still in her posession & she will be away for a week or so from tomorrow, how it will all go I dont know, one of them people who cant let things go even though I mentioned some $$, unfortunately the de-clutter consisted of empty boxes & green waste. -The plan was to inox the carb & spark throats, take the rocker cover off, have a look & inox the cams & give it a slow turn by hand before something more aggressive. Was more curious of the psi reading I should get by the cranking speed.Taking my bike apart is not an option during school holidays unless I pull the starter off while over there, I think a spare starter is on the cards now but im still taking my drill over aswell just to satisfy my curiosity
The manual quotes compression figures at 330rpm. Not sure how you'd set your drill to make sure you're at that speed. 5.5 revs per second doesn't sound too fast.
I doubt you will get any discernible or at least usable reading by hand cranking.. I would take some oil.. pour some over the cams and turn it over about a dozen times by hand... (inbox or oil down the bores as well). Then... if you have a battery impact driver or drill set at the lowest speed (drill only) spin it up and see what you get. as long as you can turn it over by hand before... and oil it up... you won't do any damage..
Put a socket on the end of the crank and see if it turns, if its stuck then game over. Then if it turns freely I would take the plugs out and put a teaspoon of oil down the bores and turn it with your drill on low speed for a few revolutions. The speed of your drill on low (most are around 850rpm no load, but turning an engine will slow that down a lot) will be close to the starter speed with no plugs. Cylinder filling wont be that much governed by speed at cranking speed compared to engine at high revs, so give it a go and see what you find.
Turn it by hand, if it rotates over freely with no binding at least some part of it is probably salvageable. I'd probably take the valve cover off while doing it to see if the cams/chain aren't shredded. I wouldn't compression test it before doing the above and seeing what condition the oil is inside, sometimes fuel could have mixed with it or water depending where it has been sitting (don't know if it's been inside the whole time) which wouldn't be good to pull through your engine with power. Just my opinion.
