Vintage Karting Forum

This is the modification that is done on the 820/610 for High RPM use. It requires grinding the needle bearing down in the rod eye and using hardened thrust washers next to the rod/bearing and then using spacers made of 7075 aluminum to set the clearance of side movement. Not easy to do. There are several people that do this. I do my own but Dave Bonbright and Terry Ives does this for customers. 

What would be the min . max gap for the shims, or how much play is usual? Also you would just grind the bearing housing not the needles?

min gap would be about .020 (no less) and then the gap grows but not very rapidly since there is little side movement. max gap i don't know. Maybe in the .040 to .045 range. You can see it clearly with the stuffer out. You have to grind the side of the bearing shell away and then the bearing have to be shortend at the same time. It took me a while to figure out how to do that. Not an easy process. At some point I may put up a Video or pics showing how that is done for the home guy without a lot of special equipment. Until then it would be best to sent them off to have done.

Steve, is this process needed for stock 820's & 610's or just those that have been modified?  I'm interested in what you are showing and look forward to you posting additional information, hopefully with pictures.

I think its a good mod. even for stock, even though any stock core 820 I bought never had a bearing issue. More rpms faster on a modified 820 is always best , seems like a mod you should have on a modified as all my modified 820s had this bearing mod done. I do have a modified 820 core that had a pin bearing failure due to this mod not being done, wasnt pretty on the inside.. Thanks for posting Steve.

The "thing to do" is just call Dave Bonbright or Terry Ives, buy the new rod, better screws and thrust washers and have them do the bearing mod at the same time. You can send your piston so they can turn your aluminum spacers to the thickness required to end up with .020 to.025 of total clearance, or you can turn your own spacers. Heat will expand the spacers, but .020 clearance is fine. I'm turning my 610's 12K with this setup, and I'm conservative on my carb settings. Zero issues at all. These engines are nearly bulletproof once these mods are done. Cheap insurance if you've spent a bunch of time and money getting ports done, plus the cost of Nikasil. TJ

I agree Ted , but I would like to learn for myself , as not to trivialize the process of the loose bearing mod , but I think this can be done by at home by someone savy enough. Isnt Dave very busy schedule wise anyways?

(01-29-2017, 05:06 PM)Art Romanelli Wrote: [ -> ]I agree Ted , but I would like to learn for myself , as not to trivialize the process of the loose bearing mod , but I think this can be done by at home by someone savy enough. Isnt Dave very busy schedule wise anyways?

Dave's ALWAYS busy. I just talked to him an hour or so ago, and he's up to his ears in Porche heads.   Steve Welte knows how to do the mod, and I could do it here, but I'd rather just let Dave do mine. If it were simply a matter of removing the ends of the bearing cup, no big deal-but you have to also mod the ends of the needles. I may be wrong, but it'd seem that you need to modify the outer race with it still pressed in the rod. I'm not sure how strong the bearing shell would be without the end cups. It might be tough pressing it back into the rod eye? Maybe Steve can weigh in on this. At any rate, I won't run any West Bends without the mods. I've seen more than one 820 partially sawn in half from a rod flailing around after breaking the rod shank, cap or screws. Ted

I use a belt sander when I grind the end of the needle bearing shell/case down. It is still in the rod. The needles are in place. I put a cut off (threads removed) 1/2" bolt in the bearing and grind the side away. This also grinds the end of the needles down. Then turn the rod around and carefully remove the bolt (all the bearing need to remain in place. Install the bolt from the other end but this time be sure to slide a washer to thrust washer over the bolt before putting it through the bearing. When you grind away the outer bearing shell you need to firmly keep pressure against the side/thrust washer, you already ground down. This will keep the bearings from moving over when you grind the shell away and your bearings will be the same length as the shell. You need to be very careful. Do not grind into the rod eye. Stop a couple thousands short of flush. You then go to a surface that you know is flat. I like to use 6" DA sand paper with sticky back in 180 grit. You still have the bolt/thrust washer/thru the rod eye. You lay the rod on the paper and sand to get the outer shell and bearings flush with the rod. Note that the big end of the rod is on the surface area laying flat. When you have that side done you can carefully remove the bolt and thrust washer from the rod eye and put it in the other side. Repeat the process. If you did all this correctly your bearing shell and bearings now are the same dimension as the width of the rod eye. Remember you must always keep pressure against the thrust washer to keep the bearings in place. If you make a mistake you can start all over with another new bearing. It takes about 3 to 4 hours to setup one piston and rod properly. Remember I am doing this at home with limited equipment. Maybe someone else can do it faster. Faster means nothing until you get on the track. I just took apart and ole 820 that had been running on a kart a long time without bearing failure but I doubt in stock form it ever turned more that 8500. I hope this info helps.

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You also need to be sure the wrist pin boss on the inside of the piston is 90* to the wrist pin. In most cases you may have to remove a bit of materiel from the piston/wrist pin boss to get it square.

(01-29-2017, 07:05 PM)steve welte Wrote: [ -> ]I use a belt sander when I grind the end of the needle bearing shell/case down. It is still in the rod. The needles are in place.  I put a cut off (threads removed) 1/2" bolt in the bearing and grind the side away. This also grinds the end of the needles down. Then turn the rod around and carefully remove the bolt (all the bearing need to remain in place. Install the bolt from the other end but this time be sure to slide a washer to thrust washer over the bolt before putting it through the bearing. When you grind away the outer bearing shell you need to firmly keep pressure against the side/thrust washer, you already ground down. This will keep the bearings from moving over when you grind the shell away and your bearings will be the same length as the shell. You need to be very careful. Do not grind into the rod eye. Stop a couple thousands short of flush. You then go to a surface that you know is flat. I like to use 6" DA sand paper with sticky back in 180 grit. You still have the bolt/thrust washer/thru the rod eye. You lay the rod on the paper and sand to get the outer shell and bearings flush with the rod. Note that the big end of the rod is on the surface area laying flat. When you have that side done you can carefully remove the bolt and thrust washer from the rod eye and put it in the other side. Repeat the process. If you did all this correctly your bearing shell and bearings now are the same dimension as the width of the rod eye. Remember you must always keep pressure against the thrust washer to keep the bearings in place.  If you make a mistake you can start all over with another new bearing. It takes about 3 to 4 hours to setup one piston and rod properly. Remember I am doing this at home with limited equipment. Maybe someone else can do it faster. Faster means nothing until you get on the track. I just took apart and ole 820 that had been running on a kart a long time without bearing failure but I doubt in stock form it ever turned more that 8500. I hope this info helps.

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You also need to be sure the wrist pin boss on the inside of  the piston is 90* to the wrist pin. In most cases you may have to remove a bit of materiel from the piston/wrist pin boss to get it square.

Thanks, Steve. About the way I thought you'd have to do it. I have a length of round stock a few thou smaller in Dia. than the wrist pin, and the length of the rod eye/thrust washer/spacer stack. I stick it thru the rod eye, then insert all the needles. using a dab of fuel soluble grease, I install a thrust washer and spacer on each side of the rod eye. I then hold the rod/washer/spacer in position in the piston and shove the wrist pin in, letting the wrist pin shove my little assembly pin out the other side of the piston. Install the retaining rings and you're ready to lube things. I invert the piston and fill it past the pin boss with thin oil. Let it sit for an hour so the oil weasels its way into the bearing good, pour out the oil and install the rod/piston in the engine. Never a failure. TJ