Vintage Dirt Bike Q & A

My 75 CR125 has a high performance MR175 engine. With the high compression it feels like the kickstarter is going to be ripped right off the bike whenever I start it. The kickstarter shaft and the knuckle splines fit together well. I tighten up the bolt as tight as I dare and loctite it but after a couple of starts it gets loose. Does anyone know of a secret way to keep the kickstarter arm tight?
If the kickstarter gear ratio was a little lower so the kickstarter spun the engine a little slower it would reduce the torque on the kickstarter gears and arm. Maybe I will look through the CR and MR parts lists to see if there was a model year that had different internal gears.

All years of the CR125 and MR175 used the same kickstarter gear parts. No difference between them other than the knuckle configurations.

It seems strange for a tight Loc-Tited bolt to repeatedly loosen. You might want to check the knuckle for thread issues or hairline cracks, or replace it with a known-good one for testing.

I think the knuckle configurations may make a difference. The large '75-'76 MR175 knuckle seems the sturdiest, with a clamp bolt and separate arm pivot pin. I've replaced my pin with an Allen bolt, drilled out the ball-bearing 'dimple' a little deeper, and shimmed up the spring, and it's held up well for years now (although I don't use it that much - see below).

I push-start my bike whenever possible - with 175 psi compression, sometimes it feels like there's a wood block in the cylinder. I'm also worried about the return spring, which is a common failure item.

I don't know if this is a factor on your bike, but the clutch cover serves as the main kickstart-shaft bearing surface. The hole can wear egg-shaped and allow the shaft to cock during starting, which isn't good for the gears and also beats on the seal. Later CR and all MR covers have steel inserts, but the early CR covers used the magnesium as the bearing and wore quickly.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric