Engine seizure

Helpful information and requests for assitance and advice
Locked
Bruno
Posts: 48
Joined: Tue Jul 07, 2015 9:42 am
Location: ABERDEENSHIRE UK

Engine seizure

Post by Bruno »

This is a first for me with any motorcycle, so I'm in unfamilair territory. My 1961 G3 has been running great all summer, no warning of any problems until close to home I felt the engine falter, then rapidly fade even though the throttle was still open ... then the back wheel locked just before I released the throttle and pulled the clutch.

I've stripped the engine down to find the problem ... not the piston in the bore as I thought might be the case. Turns out to be the big end of the connecting rod is seized between the crank flywheels - no movement at all. The crank turns OK and the movement feels smooth and free, so I think the main bearings are still good. I still don't know why this happened, but am guessing no matter what, I need to split the crankcases to get this all sorted.

I would appreciate any insights and advice from other members on the wisdom of attempting repair myself - I'm keen to have a go, but was slightly put off after reading the comment in Radco's Vintage Motorcycle Workshop quote 'anyone with a weak constitution is recommended NOT to attempt big-end renewal'.

Cheers, Bruno
Mick D
Posts: 2886
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: Engine seizure

Post by Mick D »

Hi

The big end on a G3 is a roller bearing - as your crank still rotates freely you can rule out a crank pin failure so it's probably a failure of the bearing, (fractured roller or cage).

You'll need a substantial press to replace the bearing / crank pin and also a means of setting the crank up to run true - if you have this then go ahead, if not bite the bullet and pay someone who has the equipment but more importantly the experience.

Regards Mick
User avatar
Rob Harknett
Member
Posts: 11236
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: Engine seizure

Post by Rob Harknett »

I have always got an expert do my bottom end. So for piece of mind perhaps do the same. The expert may discover what could have caused the failure and correct it
User avatar
clanger9
Posts: 1165
Joined: Sat Jun 20, 2015 9:38 am
Location: Chester, UK

Re: Engine seizure

Post by clanger9 »

It's unusual for a roller big end to seize like that. Normally they rattle and clatter long before they seize.
Is the oil pump OK? I'd look very carefully for signs of lubrication failure.

Definitely agree with Rob: assembling a roller bearing crank needs specialist equipment and plenty of experience. One for the experts...

Good luck with the rebuild!
1989 Moto Morini Dart 350
1993 Ducati 750SS
Bruno
Posts: 48
Joined: Tue Jul 07, 2015 9:42 am
Location: ABERDEENSHIRE UK

Re: Engine seizure

Post by Bruno »

Gents,

Thanks for your input and views on this ... I'm beginning to see the sense in getting this job done by an experienced outfit.

Clanger, I did wonder about an oil pump failure and I'll check this out with a view to possible causes.

Mick, have you had any dealings with Loch Ness Restorations near Inverness? I wouldn't mind using somebody that I can visit in person.

Cheers, Bruno
Mick D
Posts: 2886
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: Engine seizure

Post by Mick D »

Hi Bruno

I've no experience of Loch Ness Restorations, maybe give them a call to get a feel for their capabilities before driving up there.

I'd also suggest a call to T & L Engineering, (not in Scotland but who have a good reputation on here).

Regards Mick
Bruno
Posts: 48
Joined: Tue Jul 07, 2015 9:42 am
Location: ABERDEENSHIRE UK

Re: Engine seizure

Post by Bruno »

Hi Mick,

Thanks for getting back to me so quickly and appreciate the recommendation.

I'm contacting Loch Ness Restorations first and will let you know how that goes.

Cheers, Bruno
MikeM.
Member
Posts: 1906
Joined: Wed Jan 01, 1992 12:00 am
Location: SURREY UK

Re: Engine seizure

Post by MikeM. »

It's a long time since I had a single big end apart and can't remember if the rollers are in a cage but if it is your problem could be the roller cage breaking up and seizing up the bottom end, this happened to me many many years ago with a Messerschmitt I had, it didn't do the Conrad much good either.
User avatar
clive
Member
Posts: 5657
Joined: Mon Jan 01, 1990 12:00 am
Location: LONDON UK

Re: Engine seizure

Post by clive »

Yes they are in a roller cage. I suggest checking the oil to see if there is any sign of discolouration from the cage. If so a thorough clean out of the oiltank and oil lines will be needed.
clive
if it ain't broke don't fix
StephenG80
Posts: 264
Joined: Sun Apr 30, 2017 10:42 pm
Location: ARGYLL UK

Re: Engine seizure

Post by StephenG80 »

Give Blod who runs Twin Celts Bespoke Engineering a call (tel: 01631 720 169, email info@twincelts.com ( visit http://twincelts.com/). He does all sorts of engineering but also restores old brits and builds choppers etc.. He is not on your front door step but he is happy to have folk visit if you give him a call first). If he is too far away for you he may of someone closer. Good luck.
Locked