Engine rebuild thread

Information relating to the Matchless G2 or AJS Model 14 250cc Lightweight
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Re: Engine rebuild thread

Postby Ozmadman » Mon Oct 16, 2017 4:10 pm

dave16mct wrote:It just describes what you see in the picture.

' Airfilter for the carb. Horn (too quiet!) Spring rear leg and rear cover. The chain is sufficiently covered , no water enters. The English chain lasts a long time.'

Something like that. Dave.

thanks for that :beer:
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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Re: Engine rebuild thread

Postby clanger9 » Sat Oct 21, 2017 11:29 am

Ooh, shiny!

IMG_1734.jpg

Just got the crankcases back from Red Dragon Vapour Blasting, they look much cleaner now. 8-)
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1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: Engine rebuild thread

Postby clanger9 » Sat Oct 21, 2017 12:15 pm

The next step was to thoroughly wash & clean the crankcases and oil ways as vapour blasting tends to leave tiny glass beads everywhere.
I noticed a few debris traps that are easy to miss. Did I catch them all?

- The bottom of the oil filter housing seems to attract a lot of crud.

- There's the small breather hole that goes from the crankshaft to the oil tank:
IMG_1736.jpg

- The oil pump inlet is well hidden (you have to look through the oil tank drain hole):
IMG_1737.jpg

- Finally, there's an absolutely tiny (~1mm) oil hole in between the pushrod holes:
IMG_1735.jpg

This last one was properly blocked and I had to poke it clear...
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1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: Engine rebuild thread

Postby Ozmadman » Mon Oct 23, 2017 8:10 am

Never noticed that 1mm hole before, what is it for? and just remind me... where does that oil feed hole to the rockers go to at the bottom???
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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Re: Engine rebuild thread

Postby clanger9 » Mon Oct 23, 2017 5:33 pm

I just checked: it's an oil spray jet. It's aimed precisely at the gap between the cam followers, presumably to provide extra oil to the cam lobes.
I've put a 1mm drill in the hole in this photo so you can see where it's pointed:
IMG_1747.jpg

The other side of the hole is connected to the oil pressure feed that goes to the top end (the inner hole goes straight to the oil pump via a long gallery):
IMG_1748 (1).jpg

Interestingly, this oil jet was also blocked on the spare crankcase I have here. At ~only 1mm, it's probably prone to becoming blocked...
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1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: Engine rebuild thread

Postby Ozmadman » Mon Oct 23, 2017 5:57 pm

That's interesting!!! another mod on the later engines then as my 350 only has the oil feed to the head no secondary hole, groove and as I thought, no 1mm hole to the rockers. Maybe it is there because you have that extra hole in the crankcase by the rockers to let the oil drain in to the big end area where my hole is higher up and drains the oil back into the tank... who knows?? . I suppose you are going to tell me now that the rocker is drilled to allow some extra oil onto the camshaft? I know the early rockers were prone to wearing and the later ones were case hardened (same part number though I think so don't know how you tell which ones you have??) Mine were worn so I profiled them by hand (took ages) myself, seem to work fine.. I have another s/h pair that were worn to so I did them as spares too
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Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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Re: Engine rebuild thread

Postby clanger9 » Mon Oct 23, 2017 6:07 pm

Very interesting! Good point about the change in oil level on the later engines. The oil in my timing case will sit lower (due to the different oil return path), so maybe the oil jet was to keep the lobes oiled?

Either way, my cam followers are worn (like yours) so the modification may not have had the desired effect. New followers are unavailable, so I was wondering what to do with them! I hadn't thought of re-profiling them by hand, but I guess if the case hardening is deep enough then...

That's a really nice finish you got there, Paul. What tools did you use?
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: Engine rebuild thread

Postby Ozmadman » Mon Oct 23, 2017 6:31 pm

I don't have a vice or anywhere to put it if I did so I clamped it into my ancient B&D workmate and used a file (pushing it along the same profile as best I could) just to get it started and take the worst off. Then using various grades of wet and dry on my kitchen worktop (it's flat!) I did the same trying to keep to the original profile. Once nearly done I used fine wet and dry with some Solvol Autosol to get a finer finish, then some very fine wire wool with Solvol to polish it up then Solvol on its own to finish. Took ages but they turned out ok and work fine. There is a tiny amount of cam noise if you listen carefully when it hot but there are other noises if you listen too hard TBH as wel!! The bike runs fine with no issues. I seem to think that I read somewhere that there were "quietening ramps" on these followers but I don't know what the original profile looks like so I just did what I thought. Until the club starts selling them then we are stuck with what we have and have to make the best of it. it woud be interesting to see how they are wearing though... maybe one day when I am bored I will have a look.. cheers
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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Re: Engine rebuild thread

Postby clanger9 » Tue Oct 24, 2017 6:03 pm

Good news: the crankcase main bearings all pressed in and located fine.
IMG_1753.jpg

Bad news: the big-end bearing is marginal. The track is just beginning to break up at the edge around TDC and there's slight scuffing on the crankpin.
IMG_1751.jpg

IMG_1752.jpg

I could possibly get away with re-rollering it, but now that it's in pieces I don't want to chance it. More £££... :cry:
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1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Posts: 2309
Joined: Wed Dec 14, 2011 1:02 am
Location: ESSEX UK

Re: Engine rebuild thread

Postby Ozmadman » Tue Oct 24, 2017 8:00 pm

Did you press that timing bush in yourself? and did you have to ream it to size??
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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