after a total rebuild on the engine,valves ,guides magneto rewound etc it wont start! set magneto at 3/8" btdc,new monoblock ,cables ,what is the degree setting for the mag ? as i will have to take it apart to check it again ,many thanks
Try swapping the HR leads over. They might be the wrong way around.
already took of ht leads from mag , checked compression ,2 bar both sides ,bores were .5mmo/s honed new rings this is my first twin , causing a bit of head scratching .if anyone has the degree timing ,i would appreciate it ,
Hi Mick,
See attached . This is from my 'filing system'.
This might sound a bit basic but are you getting a spark and is fuel getting through to the cylinder. Usually the ignition timing can be a bit out and a bike still start.
Dave.
Digging further into my 'filing system' I found BSA service sheet 216. It should be the definitive info but I'd like confirmation from other SR owners.
My Rocket is timed at 35 degrees BTDC at full advance as recommended by SRM. I timed it with a strobe light and it runs fine. I found conflicting information as to 35 degs = 5/16" and 35 degs= 3/8" and I don't know which is right. As a matter of interest I have electronic ignition on it and both cylinders fire at 35degs and before using the mag the left cylinder fired ay 35 and the right at a shade over 32
Baza
Hi,
I think the 5/16 probably refers to the A7. I would suggest that the 3/8 recommended by SRM is correct. Also, with the electronic ignition it is quite easy to try slight changes to get the best running - a bit more involved with a mag and points. The other advantage of the electronic ign. is the 'wasted spark' which means that the HT leads are always the correct way round unlike a mag.
Going back to mashermick - is it running yet? If, when you put the leads back on the mag. did you try swapping them on the opposite plugs? Bear in mind that with a twin mag. it is possible to set timing 180 degs. out and that is why swapping leads on the plugs only can determine if this is the case. So if it is sparking and you have fuel this is one of the first things to try.
Dave.
thanks Dave ,checked mag by takeing of ht lead and seeing the brass p/up I know its on the right cylinder ,, after checking timing with a degree wheel ,i also did the pencil in the plug hole marked at 3/8 " .points were on the just opening mark! tempory fuel supply ,flooded ,kicked over a dozen timess and got a kickback so i MUST BE GETTING NEAR going to take of ht caps and try bare wires next
Just had a flash back to a time when my A10 would not fire/start. Having done it many times before I could not see where I was going wrong. Eventually a second opinion was sought. So repeating what I had done with a witness the exclamation was almost instant. "You are turning it backwards you wally!!!!".
Ooops! Ten minutes later the bike was running perfectly. As I had the timing cover off to change the mag. I had, for some reason, turned the engine backwards so timing was 3/8 ATDC instead of BTDC. The thing that confused me was that it did fire a bit as there would still a bit of fuel about.
A true story.
Dave.
:) :) :)
Dave.
That's brilliant, I do love to hear from honest men. I wish more folks would publish their "screw ups" it would be a help to all of us.
Mike 8) 8) 8)
ok ,so here where its at, took plugs out and wired on to plug directly good spark,kicked over about 12 times getting about 100 psi. dont know if thats enough .fitted new rings on rebuild after bore honed, fitted hepolite rings ,somebody told me they dont seal well,had a kick back but still wont fire up,having a cupper to recouperate my weak knee !
Mick,
Had look at A65 pressures and with 7.5:1 compression it should average 120/125 with a first kick of 65/70. Allowing for new rings that need bedding in, 100 psi, although a tad low, should be enough for an A10 to start and run. I know you have probably done it already but go back to the start with the timing procedure. Is there anyone near to you who could help?
See my post from the other day. Sometimes another pair of eyes can help.
Dave.
Forgive me if you've already checked this but if an auto advance mag have you wedged to full advance to check timing? Obviously if a manual advance you set to full advance. HTH
many thanks for replys, going to go back and check timing marks on pinions etc again ,keep you informed !
before your rebuild you had it running ok . I only ask as a10 and a7 have different timing marks for the valve timing but cogs are the same . I believe . Sounds like valve timing is out to me .
The early long stroke A7 used different timing pinions to the later models.
The short stroke A7 (engines prefixed AA7 BA7 and CA7) and the A10 used common pinions with the same timing marks.
One of the most common causes of failure to start after a rebuild is timing on the wrong cylinder as Dave mentions. Sometimes a kickback is caused by the excess mixture in cylinder firing on the exhaust stroke or in the silencer when ignition is 180 degrees out.
hi all , just looked at another forum that says compression tests are better done with the throttle wide open ! I didnt know that. tested again and getting about 120 psi per cylinder .going to try and start it again ,going to try and rig up a starter roller on my brake tester as my knee dont like kicking over !
ok ,checked ignition timing again ,5/16 btdc ,checked valve clearance at fireing stroke both 12 thou ,plugs out seems like a spark occaisionaly ,hard to see ! took of new carb looks ok new gaskets ,, just wont start ,not even a kick back, gona thke mag off and test !
Just timed my S/R at 3/8 BTDC then checked by disc, came out at 34 degrees.
New spark plugs do not have glazing on the porcelain. If you flood the carbs to start and it doesn't, the porcelain will saturate and short the plugs. Try new unused plugs if you haven't already.
Sometimes its the simple things that can screw you up.
Does the Mag have an ATD fitted , if so did you jam it fully advanced before timing the ignition.
If its manual, try about half retarded as fully retarded throws the internal timing of the mag out so the it is difficult to get a spark at kick over speeds.
Keep at it you will get there
ok ,removed outer and inner timing cases to check pinion marks ,all on dots an dashes , re assembled .took mag off ,built test rig ,sparks like a good one ,re fitted mag ,checked timing again,points just opening at 5/16 BTDC on fireing stroke ,checked new monoblock again ,all seems ok but the B.....D wont start although did get 2 kicks ! did what i would never do gave it a shot of easy st art ,still no go .im a single man and this is my first twin ,should have kept my B33
Where do you live? After the lock down see if someone can call by and help.
Dave.
Have you tried swapping the HT leads over.
Quote from: mashermick on 02 Apr, 2020, 14:18
ok ,removed outer and inner timing cases to check pinion marks ,all on dots an dashes , re assembled .took mag off ,built test rig ,sparks like a good one ,re fitted mag ,checked timing again,points just opening at 5/16 BTDC on fireing stroke ,checked new monoblock again ,all seems ok but the B.....D wont start although did get 2 kicks ! did what i would never do gave it a shot of easy st art ,still no go .im a single man and this is my first twin ,should have kept my B33
are you sure they are the right marks? could be one revolution out. Ive had it before. re check valve clearances after.
First thing is to try swapping the HT from one cylinder to the other, quite common to get them the wrong way around.
I see you say you set the valve clearances on the firing stroke -one exhaust valve clearance should be set when the other is fully open and the same for the inlets. That way the cearance is set when the follower is on the cam base circle not on the quieting ram.
The twin timing marks only line up one way. If they line up they are correct.
yes ,have re set tappets on the heel as suggested ,both sides valves op/close on the right stroke so should be ok on marksi, both valves closed as piston going up. going to check timing with a degree disk,seems 34 degrees is recomended by many on here ,thanks for all your replies