Topic: Honda SOHC cb750 Engine #582 Challenge Question?

[BenelliSEI]

I’ve done this a couple times with success.

I do as follows…

I clamp the motor down to the bench with some trigger/ratchet clamps (see pic below)

Once it’s secure I got more trigger clamps but reverse the ends so they open things up instead of clamp them shut (see pic below). Works as a spreader.

Strategically place 4-6 of them at the base of the cylinder and work it up with even pressure, some heat, oil and light tapping.

Just a suggestion… it’s worked for me in the past.

Good idea... right now I’m building a bolt on strap to go across the top. Thinking of slightly hanging it up fo a few days!

[MauiK3]

I wonder if applying a little pressure and vibrating the parts with a concrete vibrator or similar would jar it loose.

[BenelliSEI]

I wonder if applying a little pressure and vibrating the parts with a concrete vibrator or similar would jar it loose.

Might strap on a vibrating sander (no pad)?

[MauiK3]

Not a bad idea, leave it running for some time, might shake it loose.

[newday777]

Have you tried smacking the cylinder top with a deadblow hammer and a block across the top? If the dowels are rusted that might break loose their hold.

[BenelliSEI]

Have you tried smacking the cylinder top with a deadblow hammer and a block across the top? If the dowels are rusted that might break loose their hold.

Yes.... top, sides, all around. Frustrated.

[BenelliSEI]

This is becoming. “Long Story”. Today I cut a piece of 2” X 2” angle iron to length of the cylinder head. Marked and drilled four holes in one face, to line up with the threaded holes, between the cylinders on the barrel assembly (no picture, I forgot the IPad). On the vertical face, I drilled two holes (between each pair of cylinder cylinders) and attached about 10” of chain. Hooked in a come along winch, fastened to the ceiling above the engine stand. Lifted on the angle, until the stand was hanging with the front wheel off the ground, two rear wheels still down. I would estimate 50% of the engine weight was hanging from the ceiling. Using a length of 2 X 4 wood and a 2.5 lbs hammer, beat my way around and around on the top case. NOTHING budged. Stopped for the day, before I did any damage.

Left it hanging....... This post should be in the “supremely pissed off” thread.

[MauiK3]

Keep soaking and keep the weight on, soak while vibrating with a sander, it may help get the fluid to move in.
It will eventually let go.

[BenelliSEI]

No progress..... regular soaking and it’s been “hanging” for 2-3 days. Beat all around the seam today and nothing. This is starting to keep me awake at night!

This engine is a few hundred numbers less than this very early frame. It was probably run on a test bed and then inspected closely, before a rebuild and back on the line...... wonder what kind of adhesive they used on the base gasket?? It’s definitely working.

There is some fin damage on the RF so in addition to the hone and rings I really want to get this off to get it scrupulously clean and repair the damage. Long winter ahead!

Any more suggestions?

[Don R]

 Plywood on top of the case studs and two or three 1/4" threaded rods between the angle and plywood? I know it's asking a lot of the 4-6mm threads.
  Maybe tap the wood to set the studs or drill divots in it and put head nuts on the studs upside down?

[BenelliSEI]

Plywood on top of the case studs and two or three 1/4" threaded rods between the angle and plywood? I know it's asking a lot of the 4-6mm threads.
  Maybe tap the wood to set the studs or drill divots in it and put head nuts on the studs upside down?

Don..... I like it. I may just use a piece of 2 X  6” lumber. It’s soft enough to “plant” itself down on the studs with out damaging them. The 4 small threaded holes are the weak link, but by gently loafing it up, and then tapping away it might pop? Good idea, I needed one.

[PeWe]

You have a soft surface for lower end to land on without damages when it will come lose?

[BenelliSEI]

You have a soft surface for lower end to land on without damages when it will come lose?

PeWe…. It’s still bolted to the engine hoist which only a few m.m. off the ground.

[HondaMan]

Umm...something I've done before is:
pulled the bottom end open and released the conrods from the crank. Then the cylinders came right off, with the pistons inside them and the upper rod(s) attached. Then I used a piece of 2x2 and 2 lb sledge hammer to drive the pistons down and out by making a wooden 'cage' that I slipped over the bottom of each cylinder in turn, which was set up on some concrete blocks. I had bubble wrap tied around each rod to protect it when it fell out.

It kinda spooked me to do it, but the cylinders survived it and rebuilt fine afterward. A possible caveat: it was a K4 or K5-era engine. The cylinders in those were injection-molded, not cast like the K3 and earlier ones.

The other thing I did once (to a Honda single, I think it was a 100cc, might have been a 90cc) was pictured in these forums once using a Brit twin (BSA?) where the owner poured some gas into the well-stuck cylinders (still on the engine cases, assembled) and lit it. This both heavily heated the liners and softened the pistons and he was able to drive them downward enough to pull the cylinders up and off those vertically-split crankcases. At least Honda didn't do THAT design! The little single I did this with was pretty simple, though.

If you do either of these approaches, be sure to have the top cylinder deck milled flat again afterward. It will need at least 0.010" milled off anyway so the O-rings won't leak at the oil feed ports, so that's a good excuse?

[BenelliSEI]

Umm...something I've done before is:
pulled the bottom end open and released the conrods from the crank. Then the cylinders came right off, with the pistons inside them and the upper rod(s) attached. Then I used a piece of 2x2 and 2 lb sledge hammer to drive the pistons down and out by making a wooden 'cage' that I slipped over the bottom of each cylinder in turn, which was set up on some concrete blocks. I had bubble wrap tied around each rod to protect it when it fell out.

It kinda spooked me to do it, but the cylinders survived it and rebuilt fine afterward. A possible caveat: it was a K4 or K5-era engine. The cylinders in those were injection-molded, not cast like the K3 and earlier ones.

The other thing I did once (to a Honda single, I think it was a 100cc, might have been a 90cc) was pictured in these forums once using a Brit twin (BSA?) where the owner poured some gas into the well-stuck cylinders (still on the engine cases, assembled) and lit it. This both heavily heated the liners and softened the pistons and he was able to drive them downward enough to pull the cylinders up and off those vertically-split crankcases. At least Honda didn't do THAT design! The little single I did this with was pretty simple, though.

If you do either of these approaches, be sure to have the top cylinder deck milled flat again afterward. It will need at least 0.010" milled off anyway so the O-rings won't leak at the oil feed ports, so that's a good excuse?

Thanks for this! I had this engine running nicely a few months ago. Pistons move freely in the bores and all looks good. This is the barrel portion “glued” to the top case half..... Never seen one like this before. Very tempted to just work the head and put it all back together, but I hate being defeated by such a simple task!

[MauiK3]

I’m still thinking suspending it, heating it, and vibrating it with perhaps a random orbit sander might work it loose.

[PeWe]

Open the lower case and work from inside is probably the safest way.
Good to verify inside when engine is on the bench.

[scottly]

Thanks for this! I had this engine running nicely a few months ago. Pistons move freely in the bores and all looks good. This is the barrel portion “glued” to the top case half..... Never seen one like this before. Very tempted to just work the head and put it all back together, but I hate being defeated by such a simple task!

Why did you take it apart in the first place?? Is this a case of fixing it until it's broke?

[BenelliSEI]

Thanks for this! I had this engine running nicely a few months ago. Pistons move freely in the bores and all looks good. This is the barrel portion “glued” to the top case half..... Never seen one like this before. Very tempted to just work the head and put it all back together, but I hate being defeated by such a simple task!

Why did you take it apart in the first place?? Is this a case of fixing it until it's broke?

Yep..... the fins on the RF are damaged: I wanted to get the part really clean (vapour blasted) to do repairs, light hone and new rings. Stupid.

[MauiK3]

After all these years a look inside and the primary tensioner etc. is a good idea.

[BenelliSEI]

After all these years a look inside and the primary tensioner etc. is a good idea.

I had this motor running really well. Chains were super quiet.

[PeWe]

Recent photos of how good it look inside must be good to show a future buyer if selling it the next 5-10 years.

[BenelliSEI]

I’m going to build a top plate that sits across all the studs, then run two lengths of threaded rod down through it, connected to the 2” angle across the barrels. Pull up with the threaded rod and then when it’s nicely preloaded, bang away at the cases. If that doesn’t do it, I’ll stop.

Option two is to build a sealing plate across the top and get the entire lump vapour blasted and just leave the damn pistons where they are. I hate being defeated by what should be a simple operation..

[BenelliSEI]

Well.... Today I got the B@ST@RD apart!

Pictures and explanation next shop day. What a relief; I hate being defeated. I built the jig described earlier, but the real trick was heating up the two areas at the studs where the dowel pins are located (between the top case and the bores, both ends, front). Took lots of preload on the lifting jig and then a few solid whacks around the pins......

Definitely a few drinks before dinner tonight!

[newday777]

Congratulations on getting it apart!