Forum

[PeteF]

I must strip down very odd engines. Lots of engines I have worked on have equal sized valves.

[m1ks]

Ok, fair comment guys, I wasn't trying to be clever, merely stating that every engine I've ever stripped had unequal sized valves, the bullet is the very first 'brit' engine I've worked on.
Working as a mechanic for several years I've stripped and rebuilt my fair share of car engines and a good few bike engines I've owned, all more modern than mid seventies.
The fact remains, if the valves are of unequal sizes the inlet is ALWAYS the larger of the two for the reasons described above.

[PeteF]

Oh, total agree with that, IF the valves are different it's always the exhaust that's smaller.

[Les H]

Mind you Pete, you could have two smallish inlet valves and one larger exhaust valve. I think there are engines like this..... Just an anecdotal point...exhaust valves are always made from a more expensive higher grade steel to resist burning. Sometimes, nowadays, the same replacement exhaust valve (if it's the same size) is sold for the inlet valve as it's presumably cheaper than making another batch of inlet valves with regular inlet valve type metal....ever seen this?

[Rob]

Les, I did put some oil in via the spark plug and the comprsion was a lot better. Would you say then that I could have damaged the rings during assembly.

[Les H]

What is does say Rob is that the sealing of the valves looks reasonably ok so that's good. Sometimes the compression after a rebore can feel very good straight away, but obviously the rings need to bed in for their complete effectiveness at sealing to be achieved. For now though all you can do is to get it started as long as you can get enough compression to do so. Once it's running for a few miles the compression should feel very good but if it smokes heavily the rings might be suspect. A compression test will show how godd the rings are but that can be saved for later. As far as starting it I'm assuming you have not touched the ignition or timing gears for the points?, so they should be the same with no problems As long as you have a good spark at the the right moment (Thumb on bare spark hole should be blown off same instant when spark plug sparks as a test) Sometimes I drop a teaspoon of petrol down the plug hole, kick over once and put spark plug back in and attempt a start to get an engine to fire up....and if it does it will point to to a fueling problem with the carb. So have you broken the rings?..I cannot rule that out...but I don't want you to pull down the top end again if nothing is wrong...do you have a compression tester?

[Rob]

Yes, and after a few kiks got a reading of 7 Bar. I have had the carb virbration cleaned,
there was a lot of muck on it. Fuel was getting to the plug before but now appears to be.

[Les H]

7 bar is Ok...not great, but enough to start the engine, so rings probably ok. It could even be that the bore was a little too dry when assembled but now you have added some oil, the better sealing might help you start it. Try the neat petrol in the plug hole trick and maybe get someone to help bump start the bike..it might be ok now.

[Rob]

Les, I will try that, can you recomend a good head gASKET SEALANT.

[Les H]

Do you reckon the head gasket is leaking then? Whatever though, the Composite gskets are worth the extra expense I think they really seal well, dry or with goo. Personally I don't think jointing compound makes a lot of difference in sealing head gaskets against pressure leaks but might help as regards oil leakage out of the push rod tunnels holes. Either Wellseal or Hylomar could be used. Certainly Wellseal is the one for crankcase bare metal to metal joints. Hylomar is ok with a paper/fibre gasket. I also used Wellseal recently on a copper asbestos head gasket on my last engine build,(not Bullet) but have not used the bike yet. Wellseal requires about half an hour at least IMO to dry and become very tacky before putting the two pieces together and bolting up. I like the way you can also use a small artist brush to apply it like thick paint...brushes can be cleaned in petrol.