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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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1985, 86 CMX250C, 81 CM200T, 74 CL360, Invisible to cages, treat them accordingly. Avoids Road RAGE!
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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
 
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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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1987 CMX250C AC
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Not sure what manual you are using, my 87 oem Honda service manual would have solved your 5 piston ring question.
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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
 
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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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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
Font Line Parallel Rectangle Art


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.
Font Parallel Chair Pattern Table


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..
Font Rectangle Parallel Number Circle
 
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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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1987 CMX250C AC
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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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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???
Font Parallel Screenshot Circle Number

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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When you have an obsolete vehicle one needs to think out of the box and run all part numbers that are remotely associated with oem..
appears to be 1.00mm oversized head and cylinder base gasket, though I have never measured ID of stock head gasket.
 
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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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1985, 86 CMX250C, 81 CM200T, 74 CL360, Invisible to cages, treat them accordingly. Avoids Road RAGE!
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There is a shop here in Columbia Station that we've used on several occasions for very oddball jobs. I went to school with a member of the owners family so maybe that's why they've never turned me down.
They even bored the clutch cover for the Kickstarter that I plan on installing.
Sent you a PM with their info if you're interested.
 
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I did a search for "Honda Twin Cylinder Boring Service" that came back with several returns..
there were more
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