Honda-SOHC
General => New Member Introductions => Topic started by: FWM400four on August 18, 2025, 07:32:00 PM
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Hi all, just registered having come ax you while hunting for info on tearing down the engine on my poor old seized 400 four.
Im afraid it is a bit of a sad story, the bike was my and my ex's mode of transport back in the 80s but, long story short got stored away in my mum's garage back in the 90s. When I came to retrieve it from the garage in 2020 when Mum died it turned out the roof had caved in and it had been exposed to the elements for a long time by the state of it. So I van'd it up to Cambridge with a view to renovating it when time permitted. Having just attended my ex's funeral, I thought in remembrance, now would be an appropriate time to have a go at getting it going again.
So although it only has 25K on the clock, the state of the bike is very poor (see attached photo hopefully), anything that looked like chrome is now very rusty, but a recent visit to David Silver (museum originally but then the parts dept) suggests a lot of the bits can be replaced if not restorable.
However the main problem is the engine is seized and no amount of applying pressure to the points nut will free it. So I intended to remove the plugs and fill the pots with penetrating fluid to see if I could free it without having to resort to tearing down the top end, but the plugs were all seized and over a period of several weeks I have been gently applying penetrating fluid to them and weedling them with the result 3 have finally come out ok, but the 2nd one in from the right has snapped off leaving the thread in the head, so now I have to get the head off anyway to get that taken out.
Over the past weeks I have also been working on engine mounting bolts, engine cover screws etc and all are now free with a couple of exceptions, the main front mount bolt which is completely seized even after a lot of soaking and working, this is problem No. 1, so will need to borrow a friends torch and get some heat on that, and also the oil filter bolt which is rounded off, problem no. 2. The tensioner lock nut is free but I daren't apply any serious pressure to the tensioner bolt itself at the moment. I have also removed all the externals like crash bars, coils/plug leads, exhaust, carbs etc and given the engine a bit of a clean/degrease as it was filthy.
So finally this weekend I got going and removed the breather plate and cam/rocker housing and it all looks good inside, journals all good. I also got the 2 tensioners out ok but the chain is still too tight to go over the top of the sprocket.
Because the crank is currently unmoveable, I was hoping that the cam sprocket would be in a position for me to get at the 2 screws securing it to the cam, one is and is now loosened but the other is just down too far to get a spanner on it. So that is problem no. 3. I dont want to split the cam chain if at all possible. I have come ax a post of someone grinding down a 10mm spanner until he could just get it on the bolt, so that may be the only other option.
Problem No.4 is the 2 head nuts in the 2 inner plug wells are extremely rusty and Im anticipating will be well seized and I dont want to damage the studs, so not sure how to proceed there.
I have also noticed that although when in neutral the driven shaft is free, when I put in in gear even with the clutch pulled right in it is not, so am assuming the clutch plates are seized too, but that is down the problem order at the moment.
So any advice on any of these problems would be greatly appreciated.
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Welcome to the forum and good luck with the project. After 25 years the pistons are most likely welded to the liners with rust. Sometimes they can be freed off but other times, no amount of penetrating oil etc will move them.
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Welcome here! I see you have a big job ahead of you if you do proceed. Lots of freindly and expert advice can be found on here. :)
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Welcome to the forum.
There's plenty of advice on here so feel free to ask, no question is a stupid question.
You have a job on there but it can all be fixed, a good few of us have been in the same situation as you. Nurse Julie compiled a really good thread detailing how she restored her own 400/4 (check her reply to you and you'll see a link to her thread).
I know your bike has only done 25k but considering the state of it now I wouldn't hesitate to cut the cam chain (it's going to be worn anyway) to enable you to access the bolt to remove the cam and free the head. The two exposed head nuts seize for fun, heat is your friend her (but be careful).
Good luck and keep the progress reports coming👍.
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STOP TRYING TO TURN THE CRANK FROM POINTS SIDE,
remove the generator cover and use an impct socket on a bar on the rotor bolt.
I have just ordered oversize pistons for another member at just over £100 plus rebore, you will need a new camchain so just cut the old one with a grinder
P.s. Cambribge aint that far from Gloucester
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You say you have the exhaust off, so squirt releasing oil or diesel oil in through the exhaust ports ( inlet ports too) , some of the valves will be open and let the oil into the bores.
That bike and engine will need a complete strip down to check what needs renewing.
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Hi, welcome to the forum, you have got your work cut out there, but an interesting project with a bit of personal history as well. You are certainly looking at a full strip down of that engine just to have a good look at what’s going on regards bores bearings etc. Good luck there, go easy with the stuck components these can snap like carrots just for fun! Heat, soak, repeat…..
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welcome to the forum, lots of 400 owner here with plenty of experience to help guide you through. as already stated, heat is your freind for those tough nuts and bolts, but be carefull.
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Welcome to the sohc UK forum, were a friendly bunch.
I agree with other members, you are going to have to split the crankcase and do a full rebuild.
My 400 had not run for 10-12 years, as well as needing a rebore all four carb sliders were seized solid
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Thanks to everyone for welcome and initial advice. This is certainly going to be a challenge beyond the general maintainance to bikes and cars I'm used to but will see how it pans out!
A mate is going to lend me his blow torch so will see how that helps with the seized front engine mount bolt and 2 head nuts in the plug wells. Not used heat like this before so will be a bit of a learning experience. How long/hot do I apply it, presume I apply torque while still hot/expanded, and any tips, particularly on the 2 head nuts, they look incredibly rusty. Presume I keep applying penetrating fluid daily in between goes. Is there any mileage in splitting the nuts with a small drill if they wont come out, are they replaceble? Dont want to damage the studs, especially after my shearing the spark plug.
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Yes the nuts are available and are quite robust, use a six sided socket to undo, probably 3/8 drive long series to reach easily
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Thanks for the advice BrianJ
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Managed to get all the head bolts loosened off without damage, also all engine mount bolts now loosened and oil filter bolt loosened so can remove engine from frame when required.
Removed alternator cover/windings and tried to turn crank shaft with nut on rotor but it just started to tighten further so stopped and will see what taking off the head reveals.
Ground end off cam chain link but need a splitter/riveter to push out pin. Looked on line and there are numerous options but not clear which ones will fit the cam chain as various chain dimension standards are quoted, the pin diameter appears to be just less than 3mm and the pitch between pins about 0.3" which appears to match standard 5/16" =7.93mm = 0.312". Can anyone clarify the chain type/measurements and suggest the type/size of splitter /riveter required to split current chain and rivet new one.
Will post some pics when I get the head off.
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If you have ground the ends off the chain rivets the side plate will come of just by levering and the pins knock through with a standard pin punch, no need for expensive rivet/spliting tool
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Managed to get all the head bolts loosened off without damage, also all engine mount bolts now loosened and oil filter bolt loosened so can remove engine from frame when required.
Removed alternator cover/windings and tried to turn crank shaft with nut on rotor but it just started to tighten further so stopped and will see what taking off the head reveals.
Ground end off cam chain link but need a splitter/riveter to push out pin. Looked on line and there are numerous options but not clear which ones will fit the cam chain as various chain dimension standards are quoted, the pin diameter appears to be just less than 3mm and the pitch between pins about 0.3" which appears to match standard 5/16" =7.93mm = 0.312". Can anyone clarify the chain type/measurements and suggest the type/size of splitter /riveter required to split current chain and rivet new one.
Will post some pics when I get the head off. If my memory is still functioning ok, you will have to remove the sump to get the engine out of the frame. Have fun!!!
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Quite a lot of 400/4 owners fit this camchain, its often available at a good price.
400 cam chain Kawasaki Part No: 92057-1011
That's the primary chain Ted. Oddjob (when he's well again) sells a HD cam chain for the 400 and Nurse Julie sells one but needs joining.
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Quite a lot of 400/4 owners fit this camchain, its often available at a good price.
400 cam chain Kawasaki Part No: 92057-1011
That's the primary chain Ted. Oddjob (when he's well again) sells a HD cam chain for the 400 and Nurse Julie sells one but needs joining.
Well spotted, you are correct, hope it's not a sign of Alkasaltzer creeping into my brain.👎
I remember the tank track test now.
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If it is that solid you may want to buy ebay item 205681628665 may need boring but will clean where yours may well not clean at 1.0mm
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Whilst the engine is apart I would really, really replace the cush drive rubbers in the clutch basket. These are notorious for drying out, shrinking and cracking causing really bad backlash. Max who was a member on here used to make a full kit to replace them. I'm not sure if he still makes them but here's a link to the eBay seller who is advertising them, it could be Max but I'm not sure.
https://www.ebay.co.uk/itm/126575568549?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=CDD5i3SoTJG&sssrc=4429486&ssuid=5XpGce3OSuS&stype=1&var=&widget_ver=artemis&media=MORE
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If you want Max's email address PM me. Ted
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Thanks guys for your responses, got the block/pistons on ebay last night, so have a back up if mine are completely knackered.