Mod 20 rebuild - Tight engine

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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Cliff-1959
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Location: Cheshire UK

Mod 20 rebuild - Tight engine

Post by Cliff-1959 »

Hi Folks,
As some of you know, I am in the process of rebuilding my engine. I have now had the crank reground and fitted new main bearings, big ends and centre web shells. I have had the crankcase alloy-welded to fill a small hole. Everything feels nice and smooth with no sign of tightness.
I have cleaned all the oil ways and engine parts, so today I started the assembly.

I followed the workshop manual and everything was going really well, it all went together fine, so I decided to turn it over by the crankshaft nut - It was really tight, the exhaust camshaft also felt a little tight. I slackened off the 4 crankcase bolts and it felt normal.
Long story short, I stripped it and re-assembelled it 4 times. I tightened the bolts in different orders, and even loosely fitted the frame bolts thinking that this would line it up better, but it is still tight. Sometimes, one or other camshaft would be tight, or completely fine. Strange.

It feels like the last few turns of the bolts are jamming something up, but I can't see what. So have any of you clever peeps got any ideas? I have run out of talent :headbang:
Plodding along ...
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Duncan
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Re: Mod 20 rebuild - Tight engine

Post by Duncan »

Cliff, did you centralise the centre web?
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Cliff-1959
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Joined: Sun Apr 12, 2015 4:42 pm
Location: Cheshire UK

Re: Mod 20 rebuild - Tight engine

Post by Cliff-1959 »

Duncan wrote:Cliff, did you centralise the centre web?
I didn't, no. It didn't mention that in the manual. Excuse my ignorance, how do you do that?
Cheers,
Cliff
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Duncan
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Re: Mod 20 rebuild - Tight engine

Post by Duncan »

Cliff, assemble dry first with the centre web nuts just nipped up so that the washers can not rotate, tighten up all bolts and rotate the crank, then carefully dissemble and torque down the centre web nuts and reassemble the engine with welseal/sealant/oil filter gasket/full face gasket to suit your preference.
I was sure there was a copy of an article in the Archives (by Ken Bryant?) that covered this but can not locate it at the moment.
bjorn
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Re: Mod 20 rebuild - Tight engine

Post by bjorn »

Here is one relevant article from the archives:

Articles >> Technical Tips >> Engines >> Centre web - alignment technique

regards

Bjørn
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Cliff-1959
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Location: Cheshire UK

Re: Mod 20 rebuild - Tight engine

Post by Cliff-1959 »

Thanks very much.
I will give this a try.
Much appreciated as always. :beer:
Plodding along ...
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