Ransomes Marquis Mk4 F12 engine

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Osborne
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Ransomes Marquis Mk4 F12 engine

This is my first post on the forum and have just joined the club. I managed to find quite a nice if rather scruffy Ransomes mower and after some servicing with the ignition, a change of oil and carb clean it has sprung back to life after many years of neglect. On reassembling the fan cowell I have found that the thread is damaged for the bolt that secures the spark plug earth strap. I am based in the Bournemouth area and would like to know if anyone knows where I could hire, borrow or buy a suitable thread repair kit for the 5/16 18G thread as I cant find anyone who stocks them. Is the cylinder barrel cast iron or some alloy?

I am looking forward to completing the renovation in time for spring! Many thanks

 

NM
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Hi, I think that’s quite a

Hi, I think that’s quite a common problem. The threads are 5/16” UNC. Try searching 5/16” UNC helicoil repair kit. Check there’s enough clearance to accommodate drilling hole to next size for insert. Casing is alloy and the the tapped hole will just break through to cooling fins. 

Osborne
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Thanks for the info and I

Thanks for the info and I have seen repair kits for alloys so hopefully that will work. I note what you say about side wall thickness and find that a little concerning! 

 

wristpin
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Here you are, the drill is

Here you are, the drill is usually included in the kit but if not, 8mm or 21/64".

If your head bolt has a plain shank - not treaded all the way up to the bolt head just check that with the bolt inserted through the head the unthreaded bit does not protrude below the thickness of the head. The head gasket is very thin so if there is any doubt make sure that the thread insert is set in far enough that the shank doesn't "bottom" on it . Normally the insert is screwed in flush plus one turn.I've had my kit for years but there are plenty on fleebay at a variety of prices.  

This is the cheapest that I've found  https://www.ebay.co.uk/itm/5-16-UNC-Helicoil-Thread-Repair-Kit-Race-Rall...

Osborne
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Many thanks wristpin, I have

Many thanks wristpin, I have ordered a kit. My bolt is threaded all the way to the top by the way.

wristpin
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That’s fine. Threaded to the

That’s fine. Threaded to the top officially makes it a hex head machine screw and not a bolt, but........!!

Osborne
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All done! Head back on and

All done! Head back on and engine running as sweet as a nut! I am very pleased to report that the cylinder cuts beautifully and the clutch works well so the machine is back on song after its lengthy break. If anyone knows where to find a decent new or used muffler I would be pleased to hear.

wristpin
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Most used ones are showing

Most used ones are showing their age . May be worth asking Paul at Meetens. Villiers Parts are showing one that's not strictly correct for the F12 but will fit -  Nearly £30 !

http://www.villiersparts.co.uk/exhausts.html

Osborne
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Thanks and apologies for

Thanks and apologies for delay, have been engaged on other work! I will contact Meetens and Villiers parts and see what looks best.