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1987 Rebel 250
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Discussion Starter · #1 ·
If you've been following the saga, you know I have low compression and weak engine performance (the so-called "bobber butchering curse") in my 87' CMX250. So, I'm going to start tearing down the engine to see what I need to order. It's been almost 20 years since I've torn down an engine in auto shop class, so forgive my dumb questions.

Important questions:

1. Do I have to remove the engine from the frame to get to the pistons?

2. The ring kits look like they come with 5 rings, but the manual shows only 3 rings (beveled, regular, and wavy one). Where do the extra 2 go?

3. Do I really need that valve guide reamer? They are impossible to find.

4. What should I replace while I'm in there (e.g., valve stem seals)?

5. If I do find a bad valve, can I just replace it without doing all the lapping stuff?

6. Will a rental valve spring compressor from the auto parts store work fine?

7. I ordered a spare cylinder head (jug), but it's from a 2nd gen. I just want to make sure they're compatible.

8. Do I need a ring compressor sleeve thing to get the piston back into the cylinder?

Less important questions:

9. I ordered 1.00 oversize pistons and rings (I know, I know, I didn't have to, but I wanted to!), So what will be my new cc's once I get it bored out?

10. What are the chances the bore out will bend the connecting rods or cause other harm?

11. I'm assuming with the bore out and the EMGO shorties I'm installing, I will have to rejet. Is this correct?

I've been reading the manual over and over like I'm studying for my final exam. Any other advice or tips is greatly appreciated!
 

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1987 Rebel 250
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Discussion Starter · #4 ·
You really ought to lap all the valves, whether you replace them or not.
Just bought a hand lapper and compound! I wanna do this right.

I can answer question number one with pretty good certainty, the answer is yes! ;) It's very easy to do.
The rest are questions for the real gurus! I've forgotten so much too.o_O
Thanks! I imagine it'll make it easier anyways.
 

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Discussion Starter · #6 ·
Not sure what manual you are using, my 87 oem Honda service manual would have solved your 5 piston ring question.
View attachment 114136

Valve guide reamer is only used when new guides installed
Valve guide resize arbor is used to knurl used guides. google "Valve Guide Knurling & Resizing"
doubt you should need either..

Yes always replace valve stem seals when valve springs removed..

all valves should be lapped.. if you find a burnt valve you are going to need a machinist or engine shop with valve and valve seat grinder.. plus new valve to replace burnt one

There are several styles of valve spring compressors.. take head with you to make sure rental isn't too large..

Yes you need a piston ring compressor.. DIY in following thread
Oh! I see now. The bottom three oil rings are in the same groove. I have a 2nd gen digital manual, but the resolution is very poor and it's hard to make out some text and images.

Thank you!
 

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Discussion Starter · #8 ·
Took a few hours, but I got it torn down to the crank case. I'm not really sure what I'm looking at, but I don't see anything obviously wrong. The left piston looks pretty gross, as does the right intake valve. Cylinder walls don't seem bad. Pistons look a little streaky. Rings look and feel ok. Tired and going to bed.....
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Discussion Starter · #11 ·
Did you clean the right piston already? As you said, the left looks nasty.
I didn't clean anything yet, but the right does look way better!

Looks like the Right side #2 piston oil rings aren't doing their job and/or piston ring gaps are lined up..
I'm basing that by scorched color atop piston not the oil sitting there..
appears to me image orientation front of engine is on bottom..

you may need those larger pistons
View attachment 114144

Valve seal inspection, I'd use kerosene as it will leak through any gap and is fairly cheap and generally low flammability as long as wick/rag/paper towel isn't exposed to flame..
spills will also evaporate within a day or two, rags will dry out.
Makes a great parts cleaner too.
as one who collects antique 100+ year old kerosene lamps I can attest to that.
View attachment 114145

Lapping/grinding valves can be quite technical better left for shop to perform as they have the tools.
or you can slap some lapping compound on valve seat and hand lap..
View attachment 114146
Wow! Thanks; that's super helpful. I have 1.00 over pistons and rings on the way, and my machine shop in town will bore over for $90. I might sneak into the garage before the family wakes up and try that leak test. I have hand lapping tools on the way, but I'll see how much the shop charges. I appreciate everyone's help!
 

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Discussion Starter · #12 · (Edited)
In the morning light, I see some scratches on the Pistons, and the Piston pins look worn (should I get new ones? Or can I reuse the old?). I don't really know enough to know how bad it is though. Like I said, I already have oversized Pistons coming today.

I did the leak test with some tiki torch fuel, which I assume is kerosene LOL. To my shock and amazement, it was only a little bit of leakage on the right side after like 15 minutes. But very, very slightly. Like it was just barely moist on the valve. I dumped some kerosene in the exhaust side even though that wasn't in the instructions. That also doesn't appear to be leaking.

I'm shocked because the valves look really gross and disgusting from the outside. I will take them out and clean them and lap them in any case. I also bought new exhaust valves and all new valve seals. Apparently the intake valves are absolutely unobtainium, so I didn't find those.

Only thing that sucks is that once I deliver my cylinder to the machine shop today, they said it will take 2 to 4 weeks to get it back to me. That'll be the thing that's holding me up 😭. Maybe I can pay them extra or something to rush it lol.

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Discussion Starter · #13 ·
Dang it man. Shop said they can't bore my cylinder. Called a dozen other shops, no dice. Was gonna buy the Chinese 280cc kit, but you can't get a 1.00 gasket ANYWHERE. Speaking of which, you can't even buy a regular gasket (I ordered the only one for sale, and it's cheap Chinese garbage that didn't even fit). Speaking of cheap Chinese garbage. I bought new rings, pistons, and wrist pins for $24 shipped, so I'm sure they are the highest quality and will last forever.....

I'm just going to slap everything back together with the reused head gasket, and I'm gonna RTV the cylinder/crank instead of trying to find a gasket. Ugh, finding parts is a nightmare man!

The bobber butcher curse cannot be broken, and will never be......

I rue the day I ever laid eyes on this machine!
 

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Discussion Starter · #15 ·
did you check with an engine rebuilding or machine shop unrelated to motorcycles?

your impatience is getting the better of you.. Do some in-depth research

1st never reuse a head gasket as the cylinder edges are designed as a crush gasket, will never reseal and RTV is about the worst sealant one can use... Their are far better sealants to use none of which will seal a used head gasket..
a 1.00 gasket wouldn't have ever worked on a 57.4mm bored out bbc as it's inner diameter is 4.4mm larger than standard bore..

I find stock OEM cylinder base gasket and OEM head gasket all over the place, did you even bother to search for the 1st gen oem part numbers???
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Like I said, I can only find the cheap, flimsy, Chinese piece of tinfoil covered with cheap vinyl that they call a head gasket. Maybe you can share your secret source with me 😜
 

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Discussion Starter · #18 · (Edited)
I appreciate the help! Thank you

EDIT: It just occurred to me that I'm a complete moron (however obvious that was to everyone else already):

For some reason I thought a 1.00 piston would be 57.4mm, even though 53mm + 1mm = 54mm. I got confused and though 1.00 = 280cc aka 57.4mm big bore.

Sorry for my ignorance. I shouldn't take my frustration out on you all.

You have given me hope that I can find a 53mm head gasket &/or a 57.4mm. 54mm is no use to me now, even though I spent $200 on OEM 54mm pistons and rings (I can't get anyone to bore my cylinder).
 

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Discussion Starter · #23 ·
I can't fathom an automotive machine shop that's not eager to bore the engine. That's their bread and butter, at least with cages.
The ones I talked to said their machines can't bore something that small. I may have found a solution though: I found a guy on eBay who makes copper gaskets for the 250 CNC machine from copper. He said he can make a custom 57.4mm gasket for me. So I might buy that Chinese big bore kit after all.
 

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Discussion Starter · #25 ·
The egg roll 280cc bore kit is on its way! I'll let you all know if the cylinder crumbles in my hands when I get it lol. I just got done marinating everything in oven cleaner, so I'm gonna inspect the valves today.
 

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Discussion Starter · #26 ·
I found something to ride in the meantime--I traded my two best RC cars for a 96 CBR600F3. 0-60 in about 3 seconds! Riding this is a very, very different experience to say the least.

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Discussion Starter · #29 ·
Very true, the handling feels bizarre to me. To turn it feels like I have to counter steer a ton. When I first got on I thought the foot peg and shifter were missing or something, and then I looked like a foot and a half back of where I expected it to be and saw it. I'm trying to grip with my legs and not use my wrists, it's easier said than done. I don't plan on going over 55. I just want to bomb around the country roads and maybe commute to work. If I do anything foolish, I'm sure that my wife will find out somehow and punish me!
 

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Discussion Starter · #30 ·
Hopefully intake valve 14711-152-000 (kit from Amazon) and intake valve 14711-399-000 (only intake valve listed on Partzilla for 87 250) are the same thing, because I installed the former. I used my calipers, and they seem identical. Lapped the valves (easy) and reinstalled the valves (very hard). I also ported the intake and exhaust.

Friday, the big bore kit comes! Wish me luck!

I'm debating whether to use the big bore kit gasket (crappy, thin piece of aluminum sandwiched between plasticy material--the same one on eBay with extra holes in the gasket), or custom order a 57.4mm bore machined out of copper.
 

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Discussion Starter · #32 ·
did you bother comparing length or diamater of stem or valve seat width??
the 2nd gen intake valve had a slightly thinner valve seat width, otherwise both valves are the same

14711-152-000 was engineered for the Honda XL75 1977 to 1979 though is was used on a few 80cc and 100cc bikes in later years..
I'm not saying it won't work, but feel you are a bit impetuous..

If the old valves didn't leak as you indicated, cleaning and lapping should be all that was needed..
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Discussion Starter · #33 ·
Just got the fortune cookie big bore kit in the mail today. I'm going to try and install as much as I can after I put the kids to bed. Wish me luck!
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Discussion Starter · #34 ·
Not good. Smushed a side rail getting the cylinder on, so used a 52mm side rail which didn't really fit. Oh well. Tried again and crushed the wavy wiper ring. Cut a small piece off and reinstalled it. I'm already feeling like things are not going well at this point. Then, the big bore kit cylinder gasket is a piece of garbage and doesn't have holes big enough for the dowels. Used my drill bit to widen the holes and the cheap gasket folds and crumples and leaves sharp pieces sticking up on the holes. I put it on anyways. Everything is limping along. I try to torque the head bolts to 17ft lbs (204in lbs) and SNAP!

I don't know what to do besides just buying a new engine at this point. I don't think I can fix this. It's half past midnight and I'm pissed and hopeless.
 

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Discussion Starter · #36 ·
In case anyone is on the fence, I would NOT recommend the Chinese big bore kit:

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If it is because I put the 52 mm side rail on, then this all could be my fault. But I could not for the life of me get the pistons out of the cylinder. I started off tapping gently and then moved all the way up to a giant donkey Kong hammer and 4-ft pry bar. I'm pretty sure I destroyed all the bearings inside the crankcase. I hit that pry bar under the cylinder so hard that the engine lifted off the ground.

Now I have 300lbs of paper weights. Awesome 👍.

Price of your used bike: $300
Price of bobbing out your bike: $1000
Price of your mechanical parts: $600
Your bike now being worth $25 in scrap metal: PRICELESS!

My life is nothing more than a cautionary tale to others, full of folly, idiocy, and gratuitous suffering. Heed my word fellow rebels! Do not bob-out these classic beauties; the curse will come upon you, and you will be left taking the bus or driving your cage.
 

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Discussion Starter · #39 ·
I can't believe I'm asking this....... but is it possible to do an entire rebuild, down to the crankcase bearings? I see main bearings for sale, but no rod bearings even listed as a part. Are the rod bearings not replaceable? I'm pretty sure I destroyed every bearing in that crankcase when I beat on it like the "high striker" carnival game with the sledge and bell (not to mention the drill bit that broke off on the cam tensioner hole and fell into the abyss). I literally hit the cylinder as hard as I could with my giant sledgehammer until it broke off--do you think the lower end is toast?

The prices of used engines are insane, so that's out (plus being broke). I have a long Ohio winter where I can rebuild this puppy.
 
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