Starter Motor

[joneschri]

We have a CBR600rr engine, and with all the modification we have done to it, the starter is struggling to start the engine. There is more than enough current being delivered, i am just wondering that if now, the motor is just not up to the job. I am wondering if anyone has used an external starter motor, and if so, what sort of clutch was used on it in order to prevent it from constantly turning?

[Owen Thomas]

What kind of modifications? Did you bump up compression? Maybe stiffer valve springs? Turbo? I am having trouble imagining anything that would give the CBR starter troubles, since it is fairly robust (from my experience anyways).

Also, when you say struggling, how bad are we talking here? If the starter can get the engine up above ~400 RPM for a few seconds, it should be spinning fast enough to fire and run.

[jlangholzj]

also is the motor on a fresh rebuild? Did you try and prime the oil pump? These are tight motors after a fresh rebuild (rings,bearings, crank, springs, etc). Keep in mind that your main bearing clearances are somewhere in the 0.001"-0.0008" range and that as owen mentioned stiffer springs (even just new ones) can add up.

[joneschri]

it is a fresh rebuild, but it is only sometimes on a hot start it struggles. The compression was increased, and cams altered to a custom profile. it is spinning easily at well above 400 rpm. During the endurance driver change at hockenheim it failed to restart under its own power. went straight to the test area where it did 6 hot starts straight away. Am i missing something here?

[Z]

Originally posted by joneschri:
Am i missing something here?
Joneschri,

Dirty brushes?
Dirty or loose cable connections?
Starter motor coils burning out (ie. shorting)?
Or, as above, engine still a little tight when hot?

I would start with a new, or well rebuilt, starter motor, and check all wiring connections...

Z

[joneschri]

Cheers for the replies,

the connections are better than on the original bike, a big focus of mine this year was to ensure better current delivery to the motor.

i shall rebuild a spare and fully clean it, check for evidence of shorting other than that that should be there, and replace the bearings,
cheers.

if you think of anything else do let me know,

thanks

[Goody]

How advanced is your timing? That can cause hard cranking as well/starter kick-back.

[Warpspeed]

If its cranking at 400 rpm, but does not start, it sounds to me like something other than a starter motor problem.

One thing to check is that the ignition system still works when the starter is pulling max current from the battery. It could be very marginal and create a situation where it runs fine, and always starts first attempt, except when it doesn't.
And if it fails to start first try, the situation just gets worse as the battery depletes on subsequent attempts.

I would be monitoring a few voltages around the system during both hot and cold engine cranking, and make darned sure everything needed to run the engine still functions under worst case minimum voltage cranking conditions.

[Jay Lawrence]

I would second what Goody said. Cranking ignition should be something like 0-10° advanced. Too much more and you fight the piston. We have found that standard batteries start to struggle when you run various ancillaries, but if this was your problem you wouldn't get much cranking going on.

Another consideration is an overheated intake manifold (will cause pre-ignition and won't allow the engine to start/run properly). This could explain the fact that you could start it after a short break.

[Claude Rouelle]

I ma not an engine specialist but I can share this. I had a problem long time ago in Formula 3 when the engine tuner used a 14.9 compression ratio. We were breaking starter gear and / or flywheel teeth. At that time we did not have have access to the ECU tuning so I put a patch on patch by installing a ignition switch so that the engine was already in the 400 RPM region when the ignition was switched on. It worked.
But the best solution is to tune the ECU to reduce the timing angle (and sometimes retard it) at very low revs / starting conditions. Better include the engine temperature in the loop too: temperature influence needs different timing needs. I have seen too many engine not restarting at the driver change. There could be an issue also when the engine is "too" cold. Ask Oregon State what happened in Michigan FSAE this year. The worse can sometimes still happen to the best