Engine Knock On Start Up? Whats Cuasing this..

Ive got a 81 Csr. All stock But the coils. About 12k miles. Runs real good. It just has this knock when I first start it up. It goes away after its been running about 5 Seconds.

Ive got some info that may help solve this. It was low on oil. But I topped it off quickly after realizing this. Spark plugs are perfect. When I opened up the oil fill plug a little smoke? maybe came out. The oil looks dirty and thin. I searched and saw that thin oil may cuase it. Would my best bet at this point be to change the oil and see what happens? And the motor seems hot. What should the temprture of the heads be? Also oil leaks out from the valve cover where it meets the head. It it just a bad gasket, or is there pressure building up inside forcing it out? I removed the smog system, could this be cuasing a build up of pressure?

Thank you..
Ian

Change your oil before you run it again. You said it seems thin so make sure you put the correct 10w40 in it. With the oil leak between the head and block you've got a bad head gasket, not good. How bad is it leaking? Just a little seep or a big time leak? If it's a little seep you can probably get by with just making sure your oil level is always right before riding. If it's leaking bad you need to replace it before riding anymore.

whats the proper 10w40 to use? It gets very hot here too. I know that can affect oil selection sometimes. Its not the head gasket. Its just the one that the covers the valves up where it meets the head. And its just a small seep. Ill probaly replace it anyways. I may end up doing the valve clearances...Any ideas to why it seems hot?

If the oil is too thin a weight, or if it's started breaking down it is not lubricating as it should, which will make the motor hot. You said the plugs are good? Nice and tan in color, not white right? My 81 had the emission stuff blocked off too and it ran just fine, so I wouldn't suspect that as a cause for the problems.
I run Belray semi-synthetic in all my bikes. It's a little pricey but good oil is worth the cost. If you dont' want to use Belray use a motorcycle specific oil (car oils have cleansers in them that aren't necessarily good for wet clutch systems).

The last time I checked them After about 13 miles of Riding they were perfectly tan. Ill have to see if I can find a good bike oil. What about the filter. Should that be changed as well? If this dosent slove the problem what should my next step be?

Bullitt03737 wrote:

Would my best bet at this point be to change the oil and see what happens?

Definitely.

Bullitt03737 wrote:

Also oil leaks out from the valve cover where it meets the head. It it just a bad gasket, or is there pressure building up inside forcing it out? I removed the smog system, could this be cuasing a build up of pressure?

Thank you..
Ian

I hope you didn't remove the crankcase vent system. They have to be vented or they will have pressure from the piston stroke. All crankcases are vented in some way or another.

Bullitt03737 wrote:

Ill have to see if I can find a good bike oil.

Castrol GTX 10-40 is pretty good and available almost everywhere for reasonable price.

Bullitt03737 wrote:

What about the filter. Should that be changed as well?

Definitely.

Bullitt03737 wrote:

If this dosent slove the problem what should my next step be?

If you still hear a knock on startup that goes away after five seconds.... the fix might be ear plugs. Seriously, old engines get lower oil pressure from wear and they sometimes make noise at startup until the pump gets filled and gets full pressure up and oil to all parts of the engine. As long as it goes away quickly and there are no symptoms during normal operation: I'd ride it.

If you live where it gets pretty hot i would use the Castrol GTX 20-50 oil.(been using it since 1974 myself.)

Not sure how to quote. But what bounty hunter said about just ignoring it is probaly what will end up happening. It does go away very quickly, and dosent do it while riding. Ill see if I cant change the oil and filter tonight and see what happens.

Bullitt03737 wrote:

... When I opened up the oil fill plug a little smoke? maybe came out. The oil looks dirty and thin....

Would also sniff-test crankcase oil for any gasoline odor.

Also, you might want to switch to a heavier oil, maybe 20-50. You say it gets hot there, the thicker oil will help. If it gets cold by you, and you ride in the cold, i would switch it to 10-40.

Well. I put 20w50 in her. The first start up was brutal noise wise. But it imediatly went away. I dont think it has done it agian since then. No gas smell in the old oil either. No loss of power since Ive notiched this going on. Im at a loss to what is casing it. Oh my freind brought up a good point. What octane rating are these bikes suppose to use? Also this noise is the valve furthest away from the ground when its on the side stand so maybe it just because the oil runs away...