Model 8 Barrel bore sze

David Mills · Post by **David Mills** » Thu Sep 29, 2011 8:13 pm

Update: Barrel rebored new piston /rings and coverd 100 miles+. but I have been checking tappet adjustment and found the rocker arms dry so no oil finding its way to the rocker /arm assy from the two nipply things above the arms one more thing to find out about I'm getting weary. any thoughts cheers David

cbranni · Post by **cbranni** » Thu Sep 29, 2011 10:15 pm

Hi David, have a look at my post ........G5 lack of oil to head..........mayl give you some help.
First place I would start is the pump, check the guide pin (010079) hasn't worn, its this pin that dictates the plunger travel if its worn the pump won't pump as much oil.
It should be round with no flats, from memory its .250 dia, take care replacing it too, make sure its in the groove of the plunger as you tighten it.
If all looks ok and still no oil then off with the head and using an air gun blow down the cylinder oilway you should hear/see gurgling from oiltank, you know then the oilway is clear.
Do the same with head oilway, check you have air flow to both valves and tappets.
If all oilways are clear then its the pump, I would pull it out and check it, sod of a job, if you need further help let me know.
The rocker box should be awash with oil, if not your guides, valves and tappets wont last long.
Colin

David Mills · Post by **David Mills** » Sat Oct 01, 2011 12:58 pm

Hello Colin, I'm no AMC expert so I think I have tackled problem in reverse. Iv'e removed (in order)rocker box all clear, I tried pouring oil into the oil feed hole and turnred the engine over I thought if the pump was working it would spit it back at me it didn't so next off with its head and barrel holes all clear.Removed r/h casing, I am now looking at what at what I believe is the oil tank (heavy casing lots of bolts holding it on to crankcase)is this where the pump hides ? My bike was originally a model 8 so don't know if this is a generic design, before I start removing anymore I will wait advice. Cheers David

cbranni · Post by **cbranni** » Sat Oct 01, 2011 8:49 pm

Hi David, the bits we are concerned with are the same be it 250 or 350.
This photo shows the interal oiltank (bottom righthand corner), drain the oil if you havn't all ready done so, undo all the bolts and remove the tank
http://i1133.photobucket.com/albums/m58 ... ure069.jpg

After the tank is removed you will be able to see where the oil pump is,

http://i1133.photobucket.com/albums/m58 ... ure089.jpg

The bolt you can on the extreme left bottom corner of photo is the bolt that holds the guide pin, undo the bolt and remove, on the threaded end of the bolt is the guide pin, the end of this pin should be .250 dia round, and have no flats, this pin is nice fit in the bolt but can be removed. this item is available from JSL.
I would suggest you go as far as this at this point in time.

Colin

I have got those sizes wrong, I will find and measure some and get back to youEdited by - cbranni on 02 Oct 2011 1:41:25 PM
The pin dia is .248Edited by - cbranni on 02 Oct 2011 5:57:32 PM

David Mills · Post by **David Mills** » Sun Oct 02, 2011 8:55 pm

Hi Colin, Oil pump casing off and sat there in the bottom of the casing in a sludge is what appears to be the plug to the piston assy. Ths screw with the small spigot is loose so no wonder the oil never went north. I assume that the plug is a plug and is held by the screw. there is a spacer on the screw is this correct ? i will fit the plug back but will buy another screw as this on has a burr to one side. which way round does the plug fit. Not sure how to sent photos so I'll sent them to your Email address. So far so good, Cheers David

cbranni · Post by **cbranni** » Sun Oct 02, 2011 9:10 pm

Thats good news David, the plug goes in with the o ring, narrow groove, nearest the end, so that the tit on the bolt fits in the wider groove holding the plug in.
Email me your email address, I will send some photos
Colin

David Mills · Post by **David Mills** » Wed Oct 05, 2011 8:27 pm

Hi Colin, Bike up and running, new drive pin fitted(beware AMC Virgins like me it fits in what appears to be upside down in the screw) oil now flows freely to the rocker assy. ran round the village all seems well. many thanks Colin for all your advice and time. the forum really does work thanks again. David.

cbranni · Post by **cbranni** » Wed Oct 05, 2011 9:25 pm

Your very welcome David
Colin

BigAl350 · Post by **BigAl350** » Thu Oct 06, 2011 1:09 pm

Glad to hear it's sorted, another one back on the road!!!

I'm interested to know where you obtained the new piston and rings - the 250 is relatively easy to source but it's not too easy to find pistons for the 350 Lightweight - if anyone has a decent 350 Lightweight piston please let me know as my Model 8 has lovely piston slap - even when warm! (Still goes well though!)

Al

michael_s · Post by **michael_s** » Thu Oct 06, 2011 2:21 pm

I recently did some research and found these:

http://www.classic-motorcycles.co.uk/cg ... b_pid=6123 (JP piston)

http://www.british-only.com/estore/cate ... ze=5Edited by - michael_s on 06 Oct 2011 1:24:01 PMEdited by - michael_s on 06 Oct 2011 1:24:33 PM