Topic: Too much compression? Hard to kick

[nomad20012]

I just finished a rebuild of a 75 cb750f and went to a 836 kit. I was meticulous and made sure the rings and everything went to spec on installation.

I'm finding it very hard to kick over now and as I started to tune the engine, my battery is being drained down and being damaged under the load of struggling to spinthe engine over due to the increased resistance I'm experiencing. But it is doing so. Once its tuned it would start quicker but agaim I'm hurting my battery.

I made sure the pistons matched their respective bores and everything.

What could be going on here? I did have it running for about 30 sec to make sure everything was working and had good oil pressure. After it ran it did become about 15% easier to move the kick lever but it's still seems to take much more force than I thought normal.

This is my first overbore, will this easy up as it gets used or do I have an installation problem?

[Bodi]

It doesn't hurt a battery to be used unless you drain it close to "flat". A displacement increase shouldn't make a big difference in cranking effort, but increasing compression does. I've come across bikes that would barely turn over on the starter after a hi-comp kit went in.
Try with the spark plugs out. If it's still quite stiff, compression isn't the source. Are they hi-comp pistons?
Piston ring friction is much higher after a new rebuild until they wear in. That takes a fair bit of running but the reduced load you already feel is likely to be this.
If the bores are too tight you'll know soon enough but it's not the most likely issue. Did you assemble the engine? Tight bores feel pretty snug when a ring-less piston is inserted. Proper clearance is not "loose" in there but the piston slides without a lot of drag. Popping the head to check bore size is a pain and reusing head gaskets after torquing risks leakage. I would wait and see what happens. If the engine frees up then no sweat. If it shows signs of seizing (like lugging and stalling at idle when it heats up) be very wary.

[Patrick]

You can also get that impossible to kick, way too much copression effect if you are one tooth off on your cam timing.

[MCRider]

It doesn't hurt a battery to be used unless you drain it close to "flat". A displacement increase shouldn't make a big difference in cranking effort, but increasing compression does. I've come across bikes that would barely turn over on the starter after a hi-comp kit went in.
Try with the spark plugs out. If it's still quite stiff, compression isn't the source. Are they hi-comp pistons?
Piston ring friction is much higher after a new rebuild until they wear in. That takes a fair bit of running but the reduced load you already feel is likely to be this.
If the bores are too tight you'll know soon enough but it's not the most likely issue. Did you assemble the engine? Tight bores feel pretty snug when a ring-less piston is inserted. Proper clearance is not "loose" in there but the piston slides without a lot of drag. Popping the head to check bore size is a pain and reusing head gaskets after torquing risks leakage. I would wait and see what happens. If the engine frees up then no sweat. If it shows signs of seizing (like lugging and stalling at idle when it heats up) be very wary.

Increasing the bore increases the compression. Since the combustion chamber stays the same size, and the cylinder becomes larger, and compression is the ratio of the 2, his compression has increased over stock.

Still back to the problem at hand, I agree with Bodi as to what to do. Ultimately an 836 with slightly more compression should be startable with the electric, fairly easy. OR electric with kick assist.

[Whaleman]

MC, How exactly do you do,"electric with kick assist"? Dan

[Medyo Bastos]

a bone dry motor would also be tough to kick.  i would check oil pressure/circulation before moving forward even though you already ran the motor for 30 seconds.

[MCRider]

MC, How exactly do you do,"electric with kick assist"? Dan

That's the way James Bronson used to start his Sportster on "Then Came Bronson". You go through the motion like you're going to kick it alive, but at the point of downstroke on the kicker, hit the starter button. You'll get the benefit of both starters.  IT works good with a tough motor or tired battery.

[nomad20012]

You can also get that impossible to kick, way too much compression effect if you are one tooth off on your cam timing.

Anyone experience this?

I'm thinking back and I do remember having a hard time installing the chain on the cam. I thought if the timing was off by a tooth I wouldn't even have been able to start it?

[nomad20012]

My battery is being damaged because its one of those small ballistic Performance Evo2 batteries and they cant take the drain a conventional battery would. I could hook up a stock battery until I get it tuned which is what I'll probably do but I want find my problem before I ever crank it again anyway.

[Bodi]

Oversize pistons don't specifically need to increase compression. An 836cc kit 65mm same deck height flat top piston replacing a stock 750cc 61mm flat top piston will lift the compression ratio from 9:1 to ~10:1, true. Dropping the piston deck height 1mm will bring the CC back to ~9.25:1. Admittedly I don't know of any piston that does this.
High compression pistons, even for these overbore kits, have domed tops to raise the compression ratio. I consider 12:1 to be where "high compression" begins. The engines I saw issues with were
KZ1100s with oversize 12.5:1 pistons. You needed a different starter motor to get them turning over, I can't remember whether it was from another bike or rewound for more torque.

[PeWe]

I have noticed the same thing with new pistons. It will be easier to kickstart after some driving.
I had problem with electric starter back in the 80's. It would NOT start engine when warm. I had connected the ground cable on battery wrong, to a bolt close to toolbox beside battery, not to the frame near the engine and scratched paint to ensure good contact.

[nomad20012]

My starter is working fine. If I was off a cam tooth, would it have even ran?

[nomad20012]

the battery is sufficient to turn it over. I can barely kick it tho to give you an idea of the resistance.

[LesterPiglet]

I would check you have your cam chain on properly. I seem to remember coming across this very problem many years ago.

[Patrick]

I ran into that problem three years ago on a K5 rebuild. One tooth off and I had to stand on the kick starter. Electric starter was useless. Hondaman suggested where to check. He was right. Moved the cam chain and all was back to normal. It's worth a look.

[nomad20012]

Any way to tell if this is the case without pulling the engine?

[Patrick]

Unless you have some kind of frame kit, no. When I did it the bike would start and run, but had no power. It was just ran bad. If yours is running fairly well when it runs... I'd check compression, but unless it is very high this could be a place to look.

[Old Scrambler]

With plugs removed...........and a helper to turn the crank.......always in the correct direction........You should be able to feel the rockers gaining and losing tension on the 'off' stroke according to the stated degree of the open and closing events of your cam.  If they are about 10-degrees 'wrong' you are one tooth away from being correct. A degree wheel would make it super-accurate. 

[scottly]

Any way to tell if this is the case without pulling the engine?

How well did it run once you got it started? One tooth on the cam gear equals 21 degrees at the crank, which is a lot.
Is it still hard to kick with the spark plugs out?

[nomad20012]

It didn't run good at all but I thought it was because I had just the basics connected to get it to fire. Carbs still need some work and ignition timing not really close at all. I had to keep applying starter as it wanted to die and ith some throttle I was able to keep it firing for about 30 sec albeit with some backfire and sputtering.

Yeah its still hard with the plugs out as well.

[Old Scrambler]

21-degrees is right...........I forgot to double the value........and that makes it easier to 'feel' if it is not timed to the spec cam-events.

[scottly]

If it's hard to kick with the plugs out, it's not a compression issue. If the cam was so far out of time that valves were hitting the pistons they would either pounded clearance into the crowns or bent by now. What has been done to the motor? Any work on the bottom end, or only the big bore kit? It may just be a tight bore job that needs to be broken in. Which bore kit did you use?

[nomad20012]

bottom end was fine. Rebuilt complete top end with ebay pistons. I know I did struggle with installing the cam chain that was the only prob I had.

I don't have a degree wheel and wouldn't know how to use it if I did. I may have to learn here.

So far I'm suspecting it is off a tooth, I haven't got any other ideas that make sense so far.

[scottly]

Start the #$%*er up and break it in; cam timing won't make a motor hard to kick with the plugs out.

[nomad20012]

Start the #$%*er up and break it in; cam timing won't make a motor hard to kick with the plugs out.

Can you explain this a bit if you can?

All along I though it just needed to be broken in but I never had anything to compare it to except worn out tired bikes.