I have the older Saito 82 with plastic backplate. I got a new aluminum backplate and installed it without a gasket since the plastic one had no gasket. The crank pin rubs lightly on the new backplate.... will ordering and installing the paper thin gasket really solve the rubbing problem? (the crank has not been pushed back in a crash or anything) Thanks a bunch!

Yes it will add several 1/1000s clearance. If you still have rubbing, you can rub the front surface of the backplate on some fine emroy cloth laid on a firm flat surface to reduce the depth slightly..

The conrod rubbing is not unusual.

Ernie, you can make your own gasket quickly. Sources are endless. Some people use the thickness of magazine covers and find MA covers useful. I use manilla folder stock a lot. Trace the outline of the crankcase, and use something like a spoon to press down to indent the paper material over screw holes, etc to cut out by hand and there you go.

Thanks guys, appreciate the feedback. I am still amazed that the alum backplate leaves that small amount of clearance. On a 2-stroke yes, the case needs to be stuffed, but on a 4-stroke? Thanks.

I had to add a gasket on a 72 when upgrading to the same backplate you just bought.

The Japanese tend to be a bit anal when it comes to precision. The backplate is supposed to keep the conrod from sliding towards the rear on the rod journal.

It is normal to see where the big end of the rod has lightly rubbed the backplate in engines that have lots of useage.

Having both the old and the new 82s I replaced the plastic backplate with a alu. one and with a gasket its all good , no rubbing . As has been mentioned make one if you dont want order one in . If youve had the thing in bits maybe the collet that holds the drive hub on hasnt been tightened up and therefore the crank hasnt come forward enough . I would put one in anyway as Im sure the factory does it for a reason. Cheers the pope

Ernie, I found a SAI 82 AB gasket set on WholeSalr Trains.com but it contains no backplate Gasket. It on their page 26 I think, their site is a real pain to navigate.

True dat!

Ernie, wondering where you ordered the backplate.

I got mine from a place in England arrived in super quick time .Cant remember their name but I could go back through some records if someone REALY needs it . Didnt feel like waiting 9 mths plus here in Aus . Cheers the pope

Me too. I ordered from Hobbyplastic. It took a couple of weeks which is okay with me.

That name rings a bell . If I remember I had to wade through pages and pages of parts before I got to it . Cheers

Well i hope the thin gasket solves the rubbing problem.Can anyone tell me the reason for going to an aluminium backing plate?

I have two 82's and they both have a few years and lots of hours on them as they are my favourite engine for 46 size decathlons.During numerous tear downs to replace bent crankshafts,bearings and collateral damage like bent intake tubes,i've had no problems with the plastic backplates.You can see light witness marks on the inside of the backplate from the crankpin and perhaps the plastic is better in this regard..

No, the place I used was easy and fast. I got some other small parts too.

It was the 72 that gave all the backplate troubles. The 82 was either brand new, or about to be released. The plastic backplate would weaken and allow flexing. This would allow the intake manifold to flex in and out intermittently, causing the 72 to start running lean off and on. It was a real problem and it drove me and W8YE nuts with my engine.

The first 'fix' was to add washers under the backplate screws. Then, Saito came out with fhe improved bp. I got one and it weakened in a week or two. The ultimate fix before 82's started shipping with metal bp's is to use washers, thread locker on the screws, and to put down a bead of RTV under the shiny washer on the manifold at cylinder.

Since then, it has been a great engine. I learned some things as we were chasing our tails.

My FA150 had rub marks on the backplate but they weren't from the crank pin. They were from the connecting rod & there was a copposponding shiney rub mark in the big end of the conrod. The rub mark on the backplate was not concentric like it would be if the crank pin was rubbing. My guess is that the conrod was guided forward by the piston @ the top of the stroke while the rod was able to float to the rear near the bottom.

The purpose of the close fitting backplate is to keep the conrod from floating too far tom the rear & putting side load on the piston. Is that absolutely necessary? Probably not, but you know how the Japanese are about precision.

Horizon and Advantage Hobby both have the alum backplate in stock I think. A friend gave this one to me - think he got it from Horizon. Just a standard Saito 82 part now. It sure is a good feeling to get rid of the plastic one and reassemble it with the solid aluminum backplate. You'll need a couple of new metric bolts to mount the carb though.

Don't be afraid to run the plastic one ernie

Thanks for the answers guys re backplate material.About that rod rubbing the inside of the backplate,next time i pull an engine out i'll have a real good look at that and see.It's interesting because i've got an 82 i rebuilt about three years ago and when that flies by it makes the oddest light rubbing sound i can't descibe the tone.I wonder if that sound would be louder with an aluminium backplate? or maybe thats the engine i put a rod in backwards onto the crank.

If you put the rod in backwards it will most likely be rubbing the backplate. There is a champher on the front of the rod to clear the radius on the crank journal/web interface.

Old Fart- you can say that about the 82, but a 72 with the problem will ruin many a day until you figure it out and fix it. The 82 never has problems it seems. I left my 82 plastic backplate alone and only got one aluminum bp for the 72.