G15CSR-Current Week's DPO Discoveries

Information relating to the Matchless G15 or AJS Model 33 750cc twin. This also includes the G15 Mk II and the G15/45
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Gerard Harrison
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G15CSR-Current Week's DPO Discoveries

Post by Gerard Harrison »

Yes the BodgeMaster 750 saga continued...with some actual questions thrown in...

Cabin Fever has set in...I have run out of bits to polish, clean, repair or condemn in the warmth and comfort of the basement Man Cave.

It got into the upper 30's today so I waded through snow about 4 feet deep out to the garage to pluck off more bits of the bike to work on. Thinking to myself about the South American Rugby Team that plane-wrecked in the Andes and had the unfortunate displeasure of feasting on their comrades remains to survive...so off to the garage to pick at my mechanical carcass

Today's goal was to pull the head....the stretch goal was to get the motor out of the cradle. The head bolts and nuts were from a DPO's variety pack...three different spanners/sockets to address them...they all came out willingly much to my amazement once I determined the size. The rear underside head bolt was altogether missing so that was one chore spared. Clearly no one worried about details like applying the proper torque to any of the head assembly nuts and bolts...

The valves have some out sort of (I think) home made spring retainers...spun aluminum disks and the split keepers on two of the valves were of different dimensions on each valve.

Let me know if these strange spring retainers are some sort of special Dunstall or some-such "performance" bits...although given the state of the rest of the bike I doubt anything fancy was considered here....akin to giving a gold pocket watch to a derelict

So I grow weary rather quickly of trying to juggle the push rods up to get the head off and I move directly to my stretch goal.....pull the motor,,,,,the two remaining (incorrect) studs on the front mounting plates holding the engine in place surrendered as quickly as a trollop during Fleet Week.

Off comes the head and NOW!! on to see what sort of pistons are in here!!....hoping they still are standards....no luck .......right off the bat they are not dished tops they are flat...ok so a piston replacement was previously done (God help me)...so we begin with the scraper on the thick layer of carbon....working at it like a gambler with a lottery scratch card the truth is finally revealed...left hand piston is only a .20 over...that's ok ...

not assuming anything or leaving it to chance I begin to check the right hand piston...wow Lucky Day!! this one is also a .20 over...however its markings are nothing like the left hand piston's so some DPO used pistons from either 2 different makers or at least different production batches...not surprised....

I am hoping that I can clean and hone this .20 over bore and possibly install 2 new (matching) 20's and rings...the carbon did not indicate a lot of running time on these nor did the ridge formation at the cylinder top...I would rather save the .30/.40 for a future owner if I can...once I get the cylinder off a gauged I will have my answer

So all-in-all not a bad dead-of-winter day's progress


Now for the question....The Oil Feed to the rockers draws directly via hose from the oil tank return(?) stem/pipe...is there any advantage to using the updated method of feeding from the Timing Cover?
Edited by - Gerard Harrison on 29 Jan 2011 8:15:06 PM
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arsey30
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Location: SURREY UK

G15CSR-Current Week's DPO Discoveries

Post by arsey30 »

To remove the head with engine in frame I first removed rocker shaft spindles as per instruction manual.
One stud [rear?] was also shortened on later engines to give more clearance.

The valve gear oil supply from the return side of the pump left the rocker box quite dry, I replaced valves, guides and spindles every time I stripped the motor to fit a new drive side main bearing, so a positive supply is going to be worth it, but I am sure this has been sorted out now, I rode mine from 1966 -9.
Gerard Harrison
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Location: Nassau USA

G15CSR-Current Week's DPO Discoveries

Post by Gerard Harrison »

I should amend my numbers to be more accurately: .020, .030 etc
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John Donne
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G15CSR-Current Week's DPO Discoveries

Post by John Donne »

The oil feed modification to the rockers is well worth the effort, as you get a more positive feed to the rockers. You have to fit the later smooth rocker spindles. Get the later Commando ones, as this have a modified oil feed in the centre of them. There was many modifications made to the oiling system in 1966. Use that later Apex oil control piston rings, or just put in a set of Commando pistons. You get more power and better torque. The conrods were also drilled for a positive oil feed to the cylinder walls. The oil feed hole in the crankcase was also enlarged which would require a later larger oil feed pipe manifold. All the oiling modifications for the later Atlas engine were all detailed in the P106P, and AMC or Norton workshop manuals of the period. I do this mod to all my engines. The oil pump was also up rated from 3 speed to a six speed drive gears. This modification was also sold by Paul Dunstall in the 1960's and 70's. The only problem with these modifications would be that the motor make leak more due to higher volume of oil going around it. Use the later Commando head gasket or the flame ring one part number 063844. See Service Bulletin 3/74 dated 19/2/1974, titled Head Gaskets. Assemble WITHOUT GASKET CEMENT. Torque head as per the usual head bolts. A really good conversion would be to use the later 3/8 head head bolts, as the 5/16 ones stretch and they always blow head gaskets.
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John Donne
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G15CSR-Current Week's DPO Discoveries

Post by John Donne »

To allow the cylinder head to be removed, the rear of the barrel was made wider so you could get a spanner in to get at the nut off. Was first used on all the later G15 models, then used for all the Atlas engines. The three head studs were also shortened to allow the cylinder head to be tipped up more. All this is detailed in the P106P or workshop manuals from the 1960's. These mods must have been done after the first batch of 200 Atlas Scramblers were dispatched. The magneto was held on by a stud, so yo could not get the magneto out, as the Dommies had more room to get a spanner in to remove the nut. A nut and bolt arrangement was later used. The primary chain case had a extra stud added to stop the chain cases moving about. The early ones only had the three engine screws and the other part rested on the gearbox mainshaft. AMC or Norton Matchless did get to fix most or almost all the G15's little qwirks shall we call them, on the later models. AMC used series production so all the modifications were added to the next batch when they became available.
itma
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G15CSR-Current Week's DPO Discoveries

Post by itma »

the trick I was taught for Commandos was to lift off the head and barrel as one unit, that way you can work on it on the bench.

don't know if its possible on yours.
For what its worth I have seen worse, much much much much worse.
Gerard Harrison
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G15CSR-Current Week's DPO Discoveries

Post by Gerard Harrison »

John thank you for the excellent suggestions regarding getting the oil arterial system upgraded. As I work my way through the motor I will see what is in there now and start building a parts list....

I do recall that there is the potential for oil pooling if the system is not upgraded completely with the pump upgrade...as the subsidiary components like the spindles (and maybe banjos?) need to perform a certain amount of restriction duty and must be of correct design/aperture etc

Regards
Gerard
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