putting cases back together on a cr80?


19 replies to this topic
  • BRYANS01

Posted March 21, 2008 - 01:37 PM

#1

I know im posting this in the wrong place but the truth is i trust and know all of you guys more. So my question is i just split the cases on my sons cr 80 and relaced the crank bearings, crank, and seals now im trying to get it to go back together and i dont know if its somthing you have to manhandle together or if its suposed to just slide together. Any help would be great guys.

Thanks

  • grayracer513

Posted March 21, 2008 - 01:44 PM

#2

You usually have to tap the assembly together to get the bearings to slide onto the crank, etc., but it shouldn't be a major fight. Sometimes, and as I recall from doing my son's old CR80 the manual will specify a puller to drag the crank into its bearing, but you can still work around that with a bit of skill and prudence in most cases.

  • BRYANS01

Posted March 21, 2008 - 01:51 PM

#3

Thanks grey this is my first "bottom" end rebuild and i just wanted to make sure before i started going back together with it. Next question is should i get the crank all the way in on one side first then put it together or should i just basicaly pinch in into place at the same time?

  • grayracer513

Posted March 21, 2008 - 01:57 PM

#4

I would settle it into one side first. Normally, unless there is something about the way the engine goes together that just won't allow it, I like to install the crank in the left case first, then assemble the trans into the left case, then put the right case down over everything. That lets you have access to the ends of all the shafts that come through.

  • BRYANS01

Posted March 21, 2008 - 02:05 PM

#5

great thanks again Ill give it a try

  • wheeldude

Posted March 22, 2008 - 03:51 AM

#6

Put the crankshaft in the freezer for 5-6 hours to shrink it. Use a hotplate or propane torch to heat a socket that just fits the inside bearing race on the crank bearings. Place the heated socket on the bearings in both cases for 5 minutes or so. When they are hot, the cold crankshaft will drop in. Put the centercase gasket on, and slide the other case over the crankshaft. You might have to use the case bolts to draw the cases together the last 1/8 inch or so. If the bearings are not in the case yet, freeze them and heat the case, and they will drop in. I rebuild ALL of my 2 stroke bottom ends this way so that there is NEVER a hammer involved. Good luck, WD

  • grayracer513

Posted March 22, 2008 - 07:03 AM

#7

Heating/freezing is a good way to reduce the amount of pulling and/or driving one has to do in these situations, but let me make a couple of points.

The best way to heat case assemblies and other parts that you want to expand is an oven, or at least an outdoor grille with a thermometer. The temperature of the part can be controlled at a uniform 275 degrees that way. In the case where a main bearing is inserted in the case before the crank, avoid turning the heated assembly over, as the bearing may simply drop out.

When assembling a chilled steel part into a heated steel part, make the insertion as quickly as you can. Steel doesn't expand with heat that much and the two parts will begin to return to their normal sizes very quickly as soon as they touch each other. Finish seating them, if necessary, with a brass mallet, or a hammer and an appropriate driver.

I absolutely disagree with the practice of drawing the cases together with the case bolts. This practice can turn up the top threads in the bolt holes and cause poor seating of the sealing surface, builds a strain into the cases, and runs the real risk of distorting, or even breaking, the cases. Prudent, judicious use of a hammer is actually very much preferable, and the cases should be able to be entirely closed up before the first bolt even goes in.

  • wheeldude

Posted March 22, 2008 - 07:21 AM

#8

A quick clarification, we are talking about drawing the cases together 1/8 inch,only if the bearing cools and the crank does not fully seat, which will not distort the cases any more than judicious hammer use. I would not recommend using a hammer, brass or otherwise on the crankshaft. It is a great way to knock the crank out of true. Not trying to get in a pi$$ing contest, but after 30 + years in the industry, this is what I have found. WD

  • BRYANS01

Posted March 22, 2008 - 07:46 AM

#9

man this is why i love this site.:confused: Gray do you by chance know how much is the install tool you mentioned maybe ill just buy it and save the headache, i mean if its a 30 or 40 dollar tool is it worth the trouble of heating and cooling or would I still have to do that. Or am i just getting to a point of overthinking this rebuild?

thanks again guys

  • markryam

Posted March 22, 2008 - 08:00 AM

#10

you shouldnt need any special tools, nor should you EVER pull it together with the bolts.

lie the case on its side with the crank in one half - the main shaft and ley shaft installed with the shift drum and pegs in. warm the inner race slightly on the opposing cover and it should slide on with the aid of a few taps with a plastic mallett.


once together tap the crank from both sides to settle it in the bearings.

its pron 6 yrs since i have done cr80 bottom ends - but when i was i did loads of them and never had issues going together. coming aparts a different issue lol!!!!


mark.

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  • grayracer513

Posted March 22, 2008 - 08:27 AM

#11

A quick clarification, we are talking about drawing the cases together 1/8 inch,only if the bearing cools and the crank does not fully seat,

I understood that point completely, but IMO, based on my own 35 years of professional technical experience, it's a bad practice.

Obviously, the use of metallic (or even non-metallic) hammers or mallets carries a certain risk with it, but that's what the term judicious was intended to impart; one needs to think about what he's doing, and how. Often times, the sharp, stinging shock of an impact by brass or steel will make two parts release each other and move with less actual stress to them than they receive from softer tools, and one can cause much more permanent distortion with an improperly used press. Forcing the crank into its bearings by essentially pressing both bearings together across the span of the crankpin is hardly more conducive to maintaining alignment than a bit of well placed tapping on the shaft itself is. Having trued cranks myself, it makes it easier to decide what is excessive and what isn't, but most people aren't going to get in trouble this way if they use their heads. To some degree, that's true of drawing cases together with their bolts, as well, but I'd still much rather not.

Gray do you by chance know how much is the install tool you mentioned?

No, but genuine factory tools tend to be quite outrageously priced. What this one in particular would consist of would be a press bar that would straddle the bearing pocket, or bear directly against the inner bearing race, and a draw screw that would be threaded on the end to screw onto the end of the crank. The screw then has its own set of threads used for the actual process of pulling in the crank.

What you can substitute is a two or three jaw puller that you can use the pull against the crank nut, but these can be difficult to set up to do something different that they were designed for. As I recall, the CR80 I did was really pretty simple to work with, and I didn't need anything special.

  • BRYANS01

Posted March 22, 2008 - 11:33 AM

#12

thanks again ill try doing it tonight and post if i got it or if im buying a new case or crank

  • casperkc

Posted March 22, 2008 - 01:20 PM

#13

NEVER pull anything together with the bolts. Bad, bad, bad things happen when you "pull" things together. One other part to this is your usually 2-3" away from and totally off the right plane to do any good with those bolts anyways. Hammertime

  • todds924

Posted March 22, 2008 - 05:33 PM

#14

Put the crankshaft in the freezer for 5-6 hours to shrink it. Use a hotplate or propane torch to heat a socket that just fits the inside bearing race on the crank bearings. Place the heated socket on the bearings in both cases for 5 minutes or so. When they are hot, the cold crankshaft will drop in. Put the centercase gasket on, and slide the other case over the crankshaft. You might have to use the case bolts to draw the cases together the last 1/8 inch or so. If the bearings are not in the case yet, freeze them and heat the case, and they will drop in. I rebuild ALL of my 2 stroke bottom ends this way so that there is NEVER a hammer involved. Good luck, WD


You should NEVER use the case bolts to "draw" the cases together. That is bad news. Once the crank is settled into the left half of the case the other side should slide right together. At most a couple little taps with a rubber mallet. If it takes more than that you are doing something wrong and risk breaking or damaging something. Do not use the bolts to pull the cases together.

  • wheeldude

Posted March 23, 2008 - 05:28 AM

#15

All right gentlemen, the info I gave above come from an engine builder by the name of Eric Gorr, owner of Forward Motion, who is probably one of the midwests best Engine builders. It was printed in a book he published called Motocross and Off-Road Motorcycle Performance, which is still available at Bookstores. In the section on 2 stroke bottom end rebuilding, his technique is just as I described. Now you might want to argue the point with me, but why doubt a man who has built more engines in a year, than ALL of us have built in a lifetime. I also stated that you MIGHT have to pull the cases together, MIGHT !!!!!! I have used his method for the last 10 years with No Problems.Just my 2 cents worth, I'm done. WD

  • grayracer513

Posted March 23, 2008 - 07:28 AM

#16

Now you might want to argue the point with me, but why doubt a man who has built more engines in a year, than ALL of us have built in a lifetime.

Because, on that point, he's wrong. You should always be able to close the cases entirely without using the bolts that hold them together to do it. That applies in general to almost everything you might work on; crankcases, cam caps, case covers, and so on, with very few exceptions.

Eric Gorr is indeed a genuine authority figure in the area of motorcycle engine performance, and probably has a great deal more specific knowledge of port work, cam grinds, and other stuff than I do within that area. But with all of the respect that is certainly due him, I frankly don't think he's done that many more engines, transmissions, or other split case assemblies than I have over 35 years. Maybe he has, but the difference won't be as big as you think. At least one other member who chimed in on that was also a long time professional.

  • todds924

Posted March 23, 2008 - 04:04 PM

#17

Because, on that point, he's wrong. You should always be able to close the cases entirely without using the bolts that hold them together to do it. That applies in general to almost everything you might work on; crankcases, cam caps, case covers, and so on, with very few exceptions.

Eric Gorr is indeed a genuine authority figure in the area of motorcycle engine performance, and probably has a great deal more specific knowledge of port work, cam grinds, and other stuff than I do within that area. But with all of the respect that is certainly due him, I frankly don't think he's done that many more engines, transmissions, or other split case assemblies than I have over 35 years. Maybe he has, but the difference won't be as big as you think. At least one other member who chimed in on that was also a long time professional.

+2 Gray! I would fire any Tech i saw doing that to some motor. I can't remember the last motor i did that just didn't slip together. About the only other thing would be that once the cases are together is to check that the crank spins freely once everything is all closed up. The crank will ususally be offset a little to one side or the other in the cases preventing it from spinning free. I just determine which side needs a little bump and use a little pressure from the press to align everything.

  • YZERIK

Posted March 23, 2008 - 07:45 PM

#18

Because, on that point, he's wrong. You should always be able to close the cases entirely without using the bolts that hold them together to do it.


not sure why wheel dude keeps telling gray to pull them together with the bolts- my common sense (let alone mechanical knowledge )tells me its a bad idea

  • 02WR426Cali

Posted March 23, 2008 - 09:01 PM

#19

Just tap it with a rubber mallet and be done with it! If it doesn't go together easily then something is out of place or wrong.

  • BRYANS01

Posted March 26, 2008 - 06:13 PM

#20

just wanted to update that all is back together and i just fired it and it sounds perfect. Thanks for all the help, i ended up using a brass hammer, only about 4 or 5 taps around the crank and went right in.

thanks again





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