Unseizing 1970's 350 Jap bike

[Dick Cheeseburger]

Tentatively speaking, does anyone know a rough labour cost on unseizing a '70's J 350 4 stroke bike lump? It's seized through standing allegedly. I would need to pay someone to do the work, and wondered whether it would be best worth avoiding completely, or whether it would be relatively straightforward as far as labour goes. I'm assuming it's a fairly basic lump, but am happy to be corrected.

[LostnotFound]

Some proper grizzled bikers will be along shortly to tell you to do it yourself with a can of WD40 and a multi tool.....

 

Surely the cost isn't in freeing the piston(s) up but more in fixing whatever caused it to seize in the first place? Is it cheap enough that if you ended up punting it on as parts it wouldn't be an issue if whoever you get to look at it does a proper mechanics teeth sucking job? 

[twosmoke300]

The problem you will have with that is if Honda put the studs out in the air at the front of the barrels/ head then they may be seized solid on the alloy . My brothers 750 was a complete cunt to get apart . Ended up making a massive puller from 20mm plate which was bolted to the valve cover bolts ( about 20 of them iirc) and used the thankfully paralell to the head frame to pull against . This was after weeks of evenings heating , beating and soaking with every known penetrating fluid .

[Dick Cheeseburger]

It's an ideal bike to hack around a bit, IF the engine is cheapish to get running reliably. I wouldn't want to hack around a really good example, whereas the one I'm eying up is ripe for basic resto and customisation.

Random guess is the piston has seized in the bore due to surface rust. I guess the crank could potentially be seized as well though...

[OwdChina]

Remove plugs and shove some diesel down the bores...........leave standing for a day or two.

 

Remove clutch cover and very gently try turning clutch back an forth for any movement.

 

No movement........leave standing longer.

 

Movement........gently back an forth till full rotation achieved.

[Dick Cheeseburger]

The problem you will have with that is if Honda put the studs out in the air at the front of the barrels/ head then they may be seized solid on the alloy . My brothers 750 was a complete cunt to get apart . Ended up making a massive puller from 20mm plate which was bolted to the valve cover bolts ( about 20 of them iirc) and used the thankfully paralell to the head frame to pull against . This was after weeks of evenings heating , beating and soaking with every known penetrating fluid .

The lump in question...

[nigel bickle]

Agree with the diesel, although I tend to be quite ' liberal' with it.

 

Soaking the barrels will demonstrate seepage or not...

[OwdChina]

 I guess the crank could potentially be seized as well though...

Doubtful.........Needle bearings.

[Des]

Get a big fat bloke to bounce on the kickstarter.

[Guest]

Mix the diesel with ATF. Borescopes are brilliant in times like these, let you see if it's just stuck, or if the bore is corroded and pitted. IME 70's jap bike fasteners are made of cheese, so a rebuild of a long stood corroded lump leads to heartache..

[Dick Cheeseburger]

The problem you will have with that is if Honda put the studs out in the air at the front of the barrels/ head then they may be seized solid on the alloy . My brothers 750 was a complete cunt to get apart . Ended up making a massive puller from 20mm plate which was bolted to the valve cover bolts ( about 20 of them iirc) and used the thankfully paralell to the head frame to pull against . This was after weeks of evenings heating , beating and soaking with every known penetrating fluid .

 

Mix the diesel with ATF. Borescopes are brilliant in times like these, let you see if it's just stuck, or if the bore is corroded and pitted. IME 70's jap bike fasteners are made of cheese, so a rebuild of a long stood corroded lump leads to heartache..

It's sounding like a potential world of woe. If the bike was a few hundred ££, I'd have a punt, but this sounds like it could be a proper money pit. To add to the fun, it appears to have last been on the road in the early 1980's.

Might have be be sensible* and look at the smaller engined version of a similar 70's J locally, which turns over, but needs tanks and carb clean, but is ready to go* otherwise.

[nigel bickle]

Do everything you can to avoid extensive stripping, at least till you know.

 

If it doesn't ease off quickly, without force I'd yank it out & immerse the whole thing in a bucket of slipperiness.

 

One week to start with. That'll get it in everywhere, and ' might' help ease it over. Certainly help seep into those cheese studs, too, enabling you to save a few.

 

Paying for it? Unless you love it, ( if you can't free it,) I'd be looking for a cheap runner to surplant.

[OwdChina]

Get a big fat bloke to bounce on the kickstarter.

LOL.............Made me chuckle anyway

[blackboilersuit]

There are lots of imports appearing on ebay with "weather seized" engines. Seized is seized in my book and until you get the engine in bits you won't know why. It could be that it's just rings slightly stuck to bore and all it needs is a top end strip, clean everything up and back together with new gaskets. It could be that the (made from unobtanium) cam is covered in rust thus rendering the whole bike scrap. Forget jumping on kick start to free up seized rings. The crank will be a pressed together affair and 15 stone of enthusiastic mechanic jumping on the kick start is only going to twist the crank if the rings are stuck.

Best case is top end strip, clean everything, rebuild. I'd estimate between half and full day labour plus gaskets (circa £50).

I'd avoid like the clap unless the bike is almost free or its a rare/desirable model and you can't find a better example. 

[MikeR]

free up the clutch as well , the plates may be stuck together , and a give the cam chain tensioner a check , stripping the lump down will only lead to a divorce !

 

note ...  the air intake to the head is missing = damp in

[Jerzy Woking]

I had a 1970 250cc K1 (square tanked) version in 1977, that I bought very cheaply (had gearbox issues*) to strip and learn some mechanical skills on.

 

If you think Chinese bikes of today have shitty screws and bolts, they are like titanium compared to those on that Honda. Wouldn't touch another Japanese 4 stroke bike from that period ever again.

 

*the two gears missing from the engine still were missing after the rebuild. 2nd hand motor fixed it for far less money that new parts and gasket kit cost.

[DodgeRover]

I think the easiest way would be to pull the engine then drain the oil, remove plugs and put it upside down in a tub of diesel, filling the engine until also full through the drain plug, give it a couple of weeks then drain it out and try rocking or turning it with a ratchet strap round the flywheel or something similar.

[Guest Hooli]

Mix the diesel with ATF. Borescopes are brilliant in times like these, let you see if it's just stuck, or if the bore is corroded and pitted. IME 70's jap bike fasteners are made of cheese, so a rebuild of a long stood corroded lump leads to heartache..

 

What's the advantage of the ATF?

[PhillipM]

If you think Chinese bikes of today have shitty screws and bolts, they are like titanium compared to those on that Honda. Wouldn't touch another Japanese 4 stroke bike from that period ever again.

There's a Honda 250 stripped in the workshop. Every single nut or bolt was seized, or like cheese. Every bolt has had to be replaced, or drilled out, helicoiled, etc.

[PiperCub]

Remove plugs and shove some diesel down the bores...........leave standing for a day or two.

 

Remove clutch cover and very gently try turning clutch back an forth for any movement.

 

No movement........leave standing longer.

 

Movement........gently back an forth till full rotation achieved.

 

WHS - has worked for me in the past. Mixing either Redex or ATF can help too for some reason (not sure why though). 

 

As others have said, the fastners will be an issue with bikes of this era (not just Honda), they were bad 20 years ago when I last jacked with them!! Good luck. 

[fraybentos]

I'm new on here but...I use atf mixed with acetone works really well!

[PhilA]

What's the advantage of the ATF?

Most modern types have a degree of corrosion inhibition (which will begin to remove any ferrous corrosion but be kind to alloy surfaces), plus agents to dissolve varnish build up. Made a bit more fluid and coupled with the seeking characteristics of diesel (or acetone as mentioned above), it'll get past lightly rusty rings moderately well.

 

Phil

[UltraWomble]

Some proper grizzled bikers will be along shortly to tell you to do it yourself with a can of WD40 and a multi tool.....

Diesel down the bore for a week then take the head off.... Application of block of wood and lump hammer can be of use

[Des]

Engine may very well be merely gummed up, fossil fuels be wanting to fossilise, and if the fuel tap has been open then a tankful may have found its way in and turned to varnish. Any solvent as already mentioned will help, and I'd like to give a big shout out to paraffin as a contender, massiv respecs bruv.

The cheese engine fasteners were a brilliantly clever design feature, like having a gatekeeper checking competence on entry. We've all seen engines with every single screwhead gouged out by some chump with a Woolworths Posidriv and a lump hammer. Access denied chump.

[Guest Hooli]

Most modern types have a degree of corrosion inhibition (which will begin to remove any ferrous corrosion but be kind to alloy surfaces), plus agents to dissolve varnish build up. Made a bit more fluid and coupled with the seeking characteristics of diesel (or acetone as mentioned above), it'll get past lightly rusty rings moderately well.

 

Phil

Makes sense, thanks.

[junkyarddog]

Would getting some heat into the engine help at all?

 

Maybe place an electric radiator or similar next to the engine for a few days.

 

As already said diesel/atf mix down the bore would be good too.

[vaughant]

There's a Honda 250 stripped in the workshop. Every single nut or bolt was seized, or like cheese. Every bolt has had to be replaced, or drilled out, helicoiled, etc.

They still use the cheapest fixings now on their cars as well.

[Jerzy Woking]

Having had Japanese bikes of the 70's in the 70's, the first things to do to them were to junk the original Bridgestone tyres (of Teflon) and replace with TT100's or Roadrunners, and chage all the screws with stainless Allen screws.

[tooSavvy]

I'm new on here but...I use atf mixed with acetone works really well!

Yo..FB

 

.. some clotted cream with that yummie pie crust, eh?

 

 

Welcome

 

 

TS

[fraybentos]

Yo..FB

.. some clotted cream with that yummie pie crust, eh?

WelcomeTS

That sounds plain wrong but thanks and hi ts!