Blown engine - advice required - Updated

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Going along the motorway on Saturday and engine lost power and I saw white smoke behind me in the mirrors. Pulled in clutch, engine cut and I made it to the hardshoulder! Bike was dripping oil.

Ok, AA recovery took 2 hours but that's over with now.

What I'm thinking is piston ring/oil ring (whatever you want to call them) gone on maybe one cylinder. It's an old Kwack inline 4 so not worth much but my only form of bike transport at the moment.

To get to the point I figure a top end rebuild. I know how much the parts will be (rings x4, cam chain, tensioner, gaskets). How much would I expect for labour? - i.e. how long a job is it?

Also I've been advised the cylinder(s) maybe marked and need smoothing. How much is it for this it it's needed? - ballpark figures.
Are there going to be any other problems? I don't want to be sold a dummy by the garage. Different garage but I remember one time I was told they couldn't adjust the tappets as they haven't got the right shims (anyone explain how that works I'd like to know ). So I'm just a bit suspicious of garage mechanics now.

Just want to make sure it's a viable repair rather than going to look for a newer bike.

Thanks in anticipation
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...and the whirlwind is in the thorn trees, it's hard for thee to kick against the pricks...
Gibbs, what did Duckie look like when he was younger?

[Big Pete]

top end rebuild on an old kwak £150 ish for pistons rings etc
£55 for gaskets
£40-60 for rebore if needed
£35 for a camchain
£35 - 60 for a tensioner

if you need valves £10-15 each

if you are mechanically adept you could rebuild it in a weekend (without grinding in the valves), if a pro mechanic does it , £3-400 for labour.

The shims that the garage didn`t have sit between the cam and the valve follower, to adjust the valve clearances you take out the old shim and replace it with a thicker (or thinner) shim depending on what the clearance is. They are a common method of setting valve clearances on bikes.

Can I suggest that you get the Haynes guide to motorcycle workshop basics, it covers a lot of this sort of stuff.

as an aside, what sort of bike is it , Z650, 750, 550?
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Trust me, I`m an engineer
GarageOfPower.co.uk

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Pete, thanks for the info. Prices I have are:-
Piston Rings - set of 4 = £94
Gasket - top = £22
Gasket - bottom = £11
Cam Chain = £20
Chain Tensioner = £17
Total = £164, which I can just about live with.
All are genuine Kwak parts. Bike is a 550.

Can't do the job myself (as much as I'd like to) as lacking tools, space and time.

If total for labour is going to be around your £400 mark I think I may be better off looking for secondhand engine, or failing that a newer secondhand bike

Was surprised at tappets adjust as I'm familar with loosening screw, adjusting then tightening locking nut. No shims involved (different bike though). I know valves need shims, first time I'd been told tappets did!
____________________
...and the whirlwind is in the thorn trees, it's hard for thee to kick against the pricks...
Gibbs, what did Duckie look like when he was younger?

[Kickstart]

Hi

Labour will depend on where you go and how much they charge, but £400 is probably around 10 hours work and so entirely possible, especially if they have to drop the engine out and plenty of fasteners land up being seized in place.

Plenty of bikes used shimmed valve adjustment, whether the cams act directly on the buckets (the only non shimmed valve adjustment of valve where the cams act directly on the buckets that I can think of is the old Alfasud), or using rocker arms. Some makers have used rocker arms which can be pushed sideways to get at the shims without removing the cams.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

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Just been told secondhand engine around £400 to £450. So that's same cost as the labour for repair Wonder how much just for an engine swap?

Ok, so if I change the engine than the same could happen. Plus I'd have to do the cam chain at least at some point in the future. Hmmmh, decisions, descisions
____________________
...and the whirlwind is in the thorn trees, it's hard for thee to kick against the pricks...
Gibbs, what did Duckie look like when he was younger?

[Big Pete]

No way a gpz (or gt) 550 engine should cost £400! get onto Ebay, there was a complete gpz550 with bent forks went for less than £200

Alternatively spend £60-100 on tools and do it yourself, I`ve done this sort of work on the kerb outside my flat when I was a student.
If you are going to do it buy a complete top end gasket set and grind the valves in and replace the stem seals while you have it apart. The set also includes the exhaust gaskets which will be required.

Do you know for sure what the problem is yet?, if its just a burned valve its not as bad a job.
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Trust me, I`m an engineer
GarageOfPower.co.uk

[Robby]

The gpz engine is disposable and cheap. Its only worth stripping it down and rebuilding with new parts and gaskets if its a restoration. You'd be much better off getting a spare engine.

Danny has a spare gpz550 with a working yet high mile engine which he'd let you have for not much. Much better idea than spending 200 quid+ on fixing the existing one.

[Guest]

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Thanks for all the advice so far. I'm getting the details on Tuesday so in line with the suggestion in this thread (click here) I'll keep you posted.

I think the replacement engine is worth looking into, bearing in mind I'd only got a quote from one breaker, not IMHO noted for being one of the cheapest.
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...and the whirlwind is in the thorn trees, it's hard for thee to kick against the pricks...
Gibbs, what did Duckie look like when he was younger?

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Just got off the 'phone with the guy stripping the engine. Tells me it's melted one piston. Says barrel looks okay so pricing up bits to fix.
Will have a look at bits as sounds like could make an interesting sculpture have to laugh don't you!

Based on this I'll then decide on if worth doing, weighing up how long it'll last, how much use I'll get, how confident I'll feel with it etc.

Anyone got any clues as to what problems result in a melted piston? Was told oil channels look okay so should be getting cooling. Don't know if could be electrical fault related

Any ideas, clues appreciated as obviously if it's fixed I don't want it happening again
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...and the whirlwind is in the thorn trees, it's hard for thee to kick against the pricks...
Gibbs, what did Duckie look like when he was younger?

[Kickstart]

Hi

Melted piston is probably down to overheating on that cylinder. Either a lean mixture on that cylinder (possibly a blocked jet, possibly an air leak, possibly perforated carb diaphragm), or maybe ignition timing (although a build up of carbon on that cylinder would have a similar effect on the timing).

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Big Pete]

if its a cdi ignition (fixed timing from the crank), its likely down to a lean mixture, from any of the reasons Keith mentioned. If it has points, or has been converted to an aftermarket system the timing could be out and will need checking with a strobe. Have you changed to K& N filters or a new exhaust recently? if you have the main carb jets may need replacing, but you would usually have problems on all four pots. If you can get hold of a colourtune (made by Gunsons, its a glass sparkplug) they are excellent for checking the fuel /air mix. Last but not least, if you rebuild it make sure you regrind the valves as there may well be damage to the seats, it wont add horrendously to the job and is deffinitely worth doing.
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Trust me, I`m an engineer
GarageOfPower.co.uk

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Got back the piston - I've attached a couple of pics.
Does appear to be a hole

Best guesses so far is as stated (1) lean mixture or (2) build up of carbon on the head and/or arcing from over hot spark plug.

As far as I'm aware only plugs in the engine have been the correct temperature NGKs.

Any feedback welcome. Thanks.
____________________
...and the whirlwind is in the thorn trees, it's hard for thee to kick against the pricks...
Gibbs, what did Duckie look like when he was younger?

[Gazdaman]

When we sold an old Ducati moster 600 it was restricted to 33bhp and the garage put in the wrong spark plug which holed a piston.

are you using the correct spark plug?
EDIT: just read your above post, but have you changed to a new spark plug recently?

Gaz

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[Big Pete]

That is an absolute classic lean mixture failure,you get overheating of the piston crown followed by detonation which finally destroys the piston. I would suspect cracked carb rubbers (inlet manifolds) or leaking seals on the intake system some where. What do the other pistons look like? If they have any of the same signs the carbs have probably been badly rejetted at some point in the past. If this is the only one, its likely damaged/worn/blocked fuel system parts.
____________________
Trust me, I`m an engineer
GarageOfPower.co.uk

[ZRX61]