stock rave valves on 1mm over bore cylinders????

[hermie]

Do the rave valves need machined down for a 1mm over bore?

I bought some used cylinders (suppose to have been stock 800 bore) and they are 1mm over size. I put the top end together with my rave valves from my stock bore cylinders and when I turn it over by hand with the head off it almost seems like the pistons just barley bumping the rave valve?

or can I double the gaskets on the rave valves to get the clearance?

how many cc is a 1mm over bore 800?
thanks

 

[Chester]

They will have to be shaved. Using 2 gaskets won't make any difference.

Chester

 

[hermie]

So file or grind them down .020

I was reading else where to take a calipers and scribe .020 across the end of the rave valve then file or grind it back?

Is this the way to do it?

 

[seadoosnipe]

787cc bore?

If you bored the 787cc engine over 1 mm, you probably won't find any pistons to fit it.

The stock bore of the 787cc engine is 82.00mm or 3.228". The first bore over size, without grinding the rave valves is 82.25mm or .25 mm over bore. This makes the standard size of bore .010" over at 3.238".

Rotax does not recommend a second over bore on this engine or the 951cc due to rave configurations. Because once you shave them, you'll only be able to run them on that bore engine.

But, if you decide on a 2nd bore over, you'll take it out to 82.50mm or .50mm over bore. Which is .020" over the standard size.

I don't think I'd just file them. I'd have them cut professionally by a machinist.:cheers:

 

[hermie]

I bought a used set of pistons and cylinders they were suppose to be stock but the bore is 83mm so they are 1mm over

I took the rave valves to my step dad at a machine shop we took .025 off but when I got home they were still bumping them so I took more off with a sand paper paddle wheel in a drill util they didn't bump them at all.

should I be ok with these pistons and cylinders? They were in great shape but not stock like I was told they would be. I bought them from someone on this site.

Thanks

 

[timmyboy76]

should I be ok with these pistons and cylinders? They were in great shape but not stock like I was told they would be. I bought them from someone on this site.

Thanks

that SUX...call the dipsh** out, so we ALL know, NOT to buy from that person.

You'll be alright w/ the raves, as long as they arent hit'n.

 

[hermie]

what about the 1mm overbore
is it going to give me problems?
over heating or anything like that?

 

[timmyboy76]

jetting

i'd go up a few on both, pilot and main jets....cant say for sure, what size though....

 

[hermie]

that SUX...call the dipsh** out, so we ALL know, NOT to buy from that person.

You'll be alright w/ the raves, as long as they arent hit'n.

blk1000rr is the member

he scammed someone else so here is the info I posted in the for sale section.

I bought STOCK 800 cylinders, pistons, rings, a head and wrist pin bearings from him. He said he shipped them but when I tracked it nothing was showing, but I ended up getting the stuff a little later than I expected but not to long. Sometimes he won't answer his phone so I emailed him then he'd respond.

When I went to install this on my motor the cylinders were 1mm overbore and the wristpin bearings were for a different size motor (they wouldn't fit in the rods). I did not get the rave valves and mine would hit so I called Danny and emailed him and finally got him on the phone and he said he would see if he had the rave valves and get back to me in an hour......now he doesn't answer

So I cut my raves down.

I got a good deal on the stuff but it wasn't what it was suppose to be!!!! and now he hides and doesn't answer.

Did someone remove his ad with his phone #? or did he?

I wasn't going to post anything but I must not be the only one!

Thanks
Brian

 

[kustomkarl]

Brian PM sent...

Karl

 

[Chester]

what about the 1mm overbore
is it going to give me problems?
over heating or anything like that?

No you won't have any problems and you can leave the stock jets in there. I've installed dozens of .5mm o/s pistons or larger & just have my machinist shave the valves for me. When using piston larger than .25mm, stick to ProX, and not Wiseco, pistons.
Also, it's possible that you got a set of SBT cylinders as all of their engines are 1.0mm oversize.

Chester

 

[ski-d00]

I agree with Chester, 1mm over is no big deal, done tons of them, no need to rejet or anything.

As far as cutting the rave valves, if you took off .025" and it still hit then there is something wrong(or you mismeasured). Remember, when you bore 1mm over, your only removing .5mm or .020" around the entire perimeter. There is clearance to start with so it should not have been hitting.

Cutting the valves is very simple and can be done on a bench grinder, you don't need to take it to a machinist and only takes a few minutes. I've probably done 500 or more. Basically, you scribe a line using the leading edge of the valve to your depth, grind it carefully at the proper angle to the line, then polish with emry cloth or sand paper. The valve metal is quite soft, not hardened steel. Actually, very little metal is even removed because just the point needs cut back. Then check clearance when installed.

 

[seadoosnipe]

Scammer....

blk1000rr is the member

he scammed someone else so here is the info I posted in the for sale section.

I bought STOCK 800 cylinders, pistons, rings, a head and wrist pin bearings from him. He said he shipped them but when I tracked it nothing was showing, but I ended up getting the stuff a little later than I expected but not to long. Sometimes he won't answer his phone so I emailed him then he'd respond.

When I went to install this on my motor the cylinders were 1mm overbore and the wristpin bearings were for a different size motor (they wouldn't fit in the rods). I did not get the rave valves and mine would hit so I called Danny and emailed him and finally got him on the phone and he said he would see if he had the rave valves and get back to me in an hour......now he doesn't answer

So I cut my raves down.

I got a good deal on the stuff but it wasn't what it was suppose to be!!!! and now he hides and doesn't answer.

Did someone remove his ad with his phone #? or did he?

I wasn't going to post anything but I must not be the only one!

Thanks
Brian

Yes, I removed his advertisments and banned him from the forum. I could give you his home email but from the other members I worked with that has had problems with him, he doesn't answer emails either.

This is only the 2nd time I've seen a scammer in the forum. Our administrators are pretty good about screening these gus but it's not 100% effective.

I've pretty much always agreed with Chesters mechanical know how but I've never got a set of pistons from SBT for my 787cc engines over .020. When I order the upper end rebuild (or motors) the 787's come to me at either a standard bore or .010" over or 82.25mm. If they sold 787 or 951 pistons any other way, they'd be liable for a lawsuit. They so state that they only do Seadoo's by OEM rebuilds. Those rebuilds are done without grinding the RAVE's.

I still agree with Chester in saying it can be done, it's not hard to grind ot a rave but I don't know about 1 mm over. If the standard bore on a 787 in metric size is 82mm and the only standard bore over is .25, second bore over is .50, then that would make 1 mm over bore, 4 sizes over. If the piston now measures 83mm, you should grind the RAVE down .50mm for a 53mm piston. Wow, that's a mighty good cylinder bore...............:cheers:

 

[dsw222]

i read through this thread and noticed that nobody answered his question regarding how many cc a 1mm bored over configuration would be

anyone have an idea?