2-stroke Front Bearing

[Mike Mc]

I have a couple of old K&B .61s that I will be rebuilding this winter. I have a question about the front bearing. Should I get a shielded bearing or a sealed bearing. 

 

 

[steve too]

Model fixings have one shield for the K&B 61.

[J D 8]

If all you can get is a sealed type it is possible to remove seal on one side.

Simply bearings can supply most types.

 

[Martin Harris - Moderator]

My non-expert opinion is that a sealed bearing (2RS) with the inner seal removed is better for a 2 stroke as it should control air leakage - a possible cause of inconsistent tuning and idling problems (including failure to stop).  Replacing like for like is probably the safest "official" advice but I can't imagine a downside - anyone know different?

[Mike Mc]

1 hour ago, Martin Harris - Moderator said:

My non-expert opinion is that a sealed bearing (2RS) with the inner seal removed is better for a 2 stroke as it should control air leakage - a possible cause of inconsistent tuning and idling problems (including failure to stop).  Replacing like for like is probably the safest "official" advice but I can't imagine a downside - anyone know different?

I like that idea. I will get a bearing and see how it goes. 

 

Another question: this is more about the rear bearing. Stainless steel vs standard bearing steel. Stainless is softer but should not corrode as easily. What were the OEM bearings?

 

[Jon H]

I would go for a 2rs with inner seal removed as well but wouldnt bother with stainless or anything fancy. 

[Engine Doctor]

16 hours ago, Mike Mc said:

I like that idea. I will get a bearing and see how it goes. 

 

Another question: this is more about the rear bearing. Stainless steel vs standard bearing steel. Stainless is softer but should not corrode as easily. What were the OEM bearings?

 

OEM bearings are hardened steel . Stainless woht corrode as quickly but will wear out , as you say its softer. If you look after an engine post running then corrosion shouldnt be a problem.

Any well used engine where the bearing needed changing then I nearly always use 2rs with back seal removed. Some makes of engine would expel quite a lot of unbrunt fuel from the front bearing with associated loss of performance and economy. It cant do any harm by fitying a RS bearing to the front of engine by increasing the crankcase  compression. Infact  some bigger and well known  fourstroke engines use Sealed bearings on the rear of crank with both seals left in place. 

[Mike Mc]

I need to make a decision about changing the ring. I have spare rings. It does have fairly good compression. Is it a good idea to replace the ring or should I use the old one until the performance starts to drop off?

 

[Jon H]

If its working well i would leave it alone. The ring and bore you have are used to running together so unless the ring is dead i would leave it.

[Engine Doctor]

If its not broke dont fix it 😉.

[Mike Mc]

Is there something wrong with this piston or just the way it was manufactured?

 

[Jon H]

Is that from the K&B 61? If so spares are non existent so i wouldnt worry about it. Just put it back together and run it. If you get 6 months use out of it before it blows up then fine. If you get 6 years, great. If you get 6 minutes, its inconvenient, but there is nothing you can do about it in any case. 

[Engine Doctor]

Slightly different approach to Jon . To give it a better chance i would remove the piston ring . In the event you break it then a new one should be available from thebay . Ill pm you who to look for. After removing the ring clean the skirt with a fine green scouring pad used with plenty of oil and remove all carbon deposits . Ensure ring groove is clean being careful not to damage locating pin. Clean the inside of the liner with the same type of  scourer using a twisting in and out movement. Also clean the outside of the liner removing all gumed oil or carbon deposits , this allows better heat transfer to the outer casing also mak8ng sure that the inside of thst is clean.

An ultrasonic cleaner is a good investment to clean engine parts , beg or borrow one if you can for final cleaning. Cleanig parts in a solvent in a US cleaner is simply done by putying parts in a clean screw top jar ( old jam or sauce jar) and placing in the US cleaner then filling the US cleaner with water as usual. 

[Jonathan W]

As per Engine Doctor posting, it looks like the piston has glazed with castor oil varnish and the liner will probably be similar. I used Scotch-Brite pads to gently remove the varnish. You can clean out the ring groove by carefully scraping with a micro screwdriver. As I recall, the K&B 61 does not have a pegged ring, so you may not find a peg in the groove no matter how hard you look.

[Manish Chandrayan]

Nothing better than the broken ring to clean that ring groove. Please don't go breaking rings just to clean the groove🤣