REMOVING ENGINE OF 400F

[hippodave]

Hi All,     I am trying to remove the engine from a 400four but am having difficulty removing the lower front engine to frame bolts. The nuts are trapped in the underside of the crankcase Haynes P15.5.24. Have tried penetrating oil over several days but am starting to round the bolt heads, photo. Do I have to resort to using a blowtorch?

[Bryanj]

If you can get new bolts, grind the head off or Drill into the bolt as deep as you can at 1mm less than thread root diameter.

These tend to corrod into the nut and into the alloy case and become a real barsteward to get out.

they are also an odd ball thread pitch so you can't easily go and get a new one

[sweetpeauk]

Bolt is attached to a steel nut held captive by the crankcase, the bolt is m10 x74mm these are no longer available from Honda. If you replace these with standard nuts and bolts make sure they are 74mm as the left one is very close to a main oil gallery in the crank case and a longer bolt will crack the cases when tighten. finding a nut and bolt with a 14mm AF head will be the tricky bit. as for removing I would try heat on the captive nut.

[hippodave]

Thanks for info, much appreciated. , especially about bolt size very important for correct fit. Will source new bolts first just in case the existing ones are scrapped. Will try the blowlamp first as this worked well when the front brake pipe and bleed was undone.

[Greenbat]

Go carefully! The bolts can swell up with corrosion, and crack the lugs in the case they go through. I have an engine where said lugs fell off as soon as they saw a spanner, apparently welding up is next to impossible.

[hippodave]

Thanks, Greenbat, taken that onboard.Bike is stripped of everything apart from handlebars and wheels.With oil drained I might try turning the sucker upside down, like you do with a pushbike and have a close look at what is going on, give it a right good soaking with penetrant over a week then hit it with some heat.

[meerkat]

Thanks, Greenbat, taken that onboard.Bike is stripped of everything apart from handlebars and wheels.With oil drained I might try turning the sucker upside down, like you do with a pushbike and have a close look at what is going on, give it a right good soaking with penetrant over a week then hit it with some heat.

If you use a Flatdrive socket (six sided) instead of the conventional bi-hexagon type you'll get a better grip on the bolt head.
Also it might be better to grind off the lead-in of the socket so that it grips further down on the bolt.
Individual sockets can be bought quite cheaply to save altering one out of a complete set.

[steven400/4]

you can still get the nuts from cms
http://www.cmsnl.com/honda-cb400f-england_model14639/partslist/F01-2.html#results

[Greenbat]

Can't see the problem myself. Ok the bolt may have a odd thread, very fine IIRC but so long as you change the nut as well as the bolt and the length is right you can use any 10mm bolt. I replaced all my engine bolts with stainless 30 years ago, best bet is to make sure you grease them BEFORE you fit them as it stops the corrosion starting and ending up like this.

I'd be careful using stainless in high stress areas, as it is more brittle than steel. Plus, SS and ally corrode very badly.
Returning to that one of mine that had the lugs fall off-they literally did that, the corrosion had already swollen up and broke the casting.

Maybe, your best bet is turn it upside down and use a dremel on the nut. It'll take ages, but should be the least risky. Drilling down the middle may work, but if you break into the ally it'll cut that instead of the steel.

[PatM]

And don't do what I once did- put the wrong length bold in, tighten it up, and it cut right into the crankcase :-( engine was a write-off but in the 80's, they were 2-a-penny.