Topic: Honda SOHC cb750 Engine #582 Challenge Question?

[BenelliSEI]

Stripped off the head on this very early engine. Been soaking the base gasket and down through the head studs for a while, but it’s stuck solid. What do you suggest?

[PeWe]

Pistons free, cylinder stuck?

Early shop guy has sealed (glued) base gasket  on both sides with old good Permatex Aviation no 3?

Open lower case, take everything out and carefully push cylinder out from inside after heating it up for a few hours for even temperature.

[BenelliSEI]

Pistons free, cylinder stuck?

Early shop guy has sealed (glued) base gasket  on both sides with old Permatex Aviation no 3?

Open lower case, take everything out and carefully push cylinder out from inside after heating it up for a few hours for even temperature.

PeWe..... Pistons are free (the engine ran well before I started restoration of the bike). Bottom end was super quiet, totally original, never out of the frame. I am not opening it up. There appears to be no extra sealant, or that it had ever been apart. The head lifted off easily!

I’ll try a small, sharp knife and see if I can separate the base gasket in two?

[PeWe]

It might be the 2 dowel pins that are stuck in case and cylinder?
Massage with some heat that make alu to swell a little, the holes for dowel pins too. Penetrating oil in the 2 outer front stud holes already there, right?

[MauiK3]

I’m with PeWee, split the cases, do the primary drive, check the crank and push the cylinders off from below.
If you get the rods and pistons are out you can make a pulling fixture to grab the bottom of the cylinder.

[BenelliSEI]

It might be the 2 dowel pins that are stuck in case and cylinder?
Massage with some heat that make alu to swell a little, the holes for dowel pins too. Penetrating oil in the 2 outer front stud holes already there, right?

Probably the pins.... soaking down all the studs.

[BenelliSEI]

I’m with PeWee, split the cases, do the primary drive, check the crank and push the cylinders off from below.
If you get the rods and pistons are out you can make a pulling fixture to grab the bottom of the cylinder.

Very low mileage, ran very quiet with no primary chain noise and no leaks. Don’t want to split it.....

[ekpent]

Are you just doing the head gaskets and pucks or going further and doing rings and a hone also ?

[BenelliSEI]

I have a new set of std. Honda rings, so very light hone and rings for sure. I want to get the head and barrel really clean, so going to try hydro jet all the parts.

Also, a couple of bent fins I want to repair properly…..

[HondaMan]

Can I [be honored] to send you a couple of the thicker O-rings you'll need inside the 2 oil ports in the head gasket when you bolt it all back up?

[BenelliSEI]

Can I [be honored] to send you a couple of the thicker O-rings you'll need inside the 2 oil ports in the head gasket when you bolt it all back up?

That would b great! Hold on and I’ll remind you when the time comes. I’m determined not to. Rush. This one and just poke along at it. Much appreciated. John D.

[HondaMan]

Can I [be honored] to send you a couple of the thicker O-rings you'll need inside the 2 oil ports in the head gasket when you bolt it all back up?

That would b great! Hold on and I’ll remind you when the time comes. I’m determined not to. Rush. This one and just poke along at it. Much appreciated. John D.

I always have them!

[PeWe]

Another thread were the thicker o-rings were up. Link to compression calculation. Hondaman's post just before.
(Stock 11x2.5 vs thicker 10.78x2.62mm)

http://forums.sohc4.net/index.php/topic,153549.msg2203559.html#msg2203559

- 1.0mm thick head gasket need thicker o-rings.
- 0.8mm head gasket stock o-rings.
This with stock cylinder not much decked.

Easy to measure and calculate o-ring compression that shall be between 20-30%.

See link to an o-ring supplier were compression ratio is described.

[BenelliSEI]

Thanks PeWe. Assuming I ever get it apart!

[BenelliSEI]

Still stuck! Soaked it again yesterday. Turbo torch is next. This is headed to the “pissed off” thread!

[MauiK3]

another crazy (extreme) idea, maybe a little better thought through

Remove the crank and pistons
Fabricate circles of strong plywood to fit under the cylinder sleeves lower skirt
Attach slide hammers to the center of perhaps two, maybe two and three or maybe alternate
Lash the upper case down to something solid
Try the slide hammers (as gently as possible) to see if they will break it loose
If it dislodges the sleeves you can fix that easily
I know, pretty extreme and hair brained
It's a disease, I'm always thinking up tools for tough jobs, some work, some ideas are not thought through

[Don R]

 Pretend you're trying to just swap the head, the cylinder will come loose every time. L0L!
  I remember a pic of someone that hung the cylinder from a rope hoping the weight of the engine would eventually pull it apart. I don't think that worked either.

[RAFster122s]

Doesn’t fire work? Heard of a few people filling cylinders with gas and setting alight and the heat will break the bond by the time the gas is burned off. It is a rough way to do it but when all else fails…

[PeWe]

Risk I repeat myself when lobbying for one way taking it apart.

Pistons runs free so only thing that bond cylinder and case together are the 2 dowel pins.
They have changed in lenght during the years.

Honda factory might have used slightly too long dowel pins that dug into case and cylinder when they slammed it together? The pins have sharp ends.

Maybe cylinder was seated with help of heavy nylon mallet before tighten the head that finalized it.
This engine is among the earlier numbers. Honda factory must have improved how to produce parts and assemble them during the years.

Try to bend cylinder off might cause damage.
So back to open lower case, crank with rods + pistons out.
A wooden u-shape wooden "tool" that can press sleeve 1 and 4 simultanously with help of a heavy hammer that does not need to hammer hard.

Heat gun that has warmed the case under the cylinder making the dowel pins to leave easier.

Open the engine for inspection must be OK for future value?

If cylinder never has been off, sealer gluing it together must  cannot be the case here.

[MauiK3]

That’s another reasonable approach

[Kevnz]

Do you have a bbq big enough to take it? Worked for me stripping a chainsaw and various bike bits, brake caliper bleed nipple for one.

[RAFster122s]

Rusty caliper bleeder screws can often be released using a double boiler with enough paraffin wax to submerge the bleeder screws area of the caliper. You cook it in the wax for about 30 minutes while outside away from any structures using your bbq grill or a hot plate capable of boiling the water for the double boiler. Needs to be in a safe area and you need to be careful as the hot wax can both catch fire as well as provide life threatening burns. The steam is also a risk...

But, this doesn't sound like a rusty issue that could utilize that method.

A BBQ grill could provide a means of heating up the cylinders and block to very high temps. Just bolt up a chain for a cherry picker hoist or engine hoist to pull the motor off the grill while hot. Relocating it to a worktable you prep to work on the hot motor to separate the recalcitrant cylinder assembly while things are good and hot using some ash or oak wedges to drive between the cylinders and block... Just take care you are working in areas that won't destroy more fins.

Also,you can use charcoal and mock up a temporary grill pit using concrete cinder block and stones or sheet steel.
I would invert things and have the piston and cylinders closest to the flames as you don't want to cook the primary drive anymore than needed so you aren't needing to rebuild the primary drive replacing the rubbers if they are still good.

Unfortunately it sounds like you are going to have to tear the bottom end down to separate the cylinder using the other advice that has been offered if a bit of time with heat doesn't do the trick.

Good luck John!

[Kelly E]

Is there a spot down in the cam chain tunnel that you can catch with a custom made hook for the slide hammer?
I had to use my 10lb slide hammer to get the clutch cover off the 75' CB 400-4 to replace the clutch. The 2.5lb slide hammer wouldn't break the cover loose, it was the original clutch.

[BenelliSEI]

Is there a spot down in the cam chain tunnel that you can catch with a custom made hook for the slide hammer?
I had to use my 10lb slide hammer to get the clutch cover off the 75' CB 400-4 to replace the clutch. The 2.5lb slide hammer wouldn't break the cover loose, it was the original clutch.

Will have a look.... nervous about any single point load that might break it......

[WideAWAKE]

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.