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Post by doulsy on Mar 22, 2015 17:28:21 GMT
Just about to change the plug on my 125 lml engine and the plug i took out is a b7hs the one i have been supplied with is a b8es which has a longer thread, will this do any harm?
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Post by phattanglo on Mar 22, 2015 17:45:19 GMT
Longer thread means it will screw in further with a risk of contacting the piston at the top of the stroke, could do some damage.
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Post by doulsy on Mar 22, 2015 18:18:38 GMT
Longer thread means it will screw in further with a risk of contacting the piston at the top of the stroke, could do some damage. sh*t, i put it in and it started up, i have now removed it, cheers i will order the proper one |
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Post by Robjack on Mar 22, 2015 18:42:21 GMT
If it started up, it's OK. The damage would have been done on the first stroke of the piston if it was too long. Whether it's the right plug for your set up is a different matter.
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Post by doulsy on Mar 22, 2015 19:01:58 GMT
If it started up, it's OK. The damage would have been done on the first stroke of the piston if it was too long. Whether it's the right plug for your set up is a different matter. I got it from a company that i had bought some stuff from, i have a 1978 p200e but im not sure if i told them i had put a 125 lml engine in as my 200 engine is needing mega work, think they have maybe gave me a plug for the p200 engine. |
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Post by moomoo on Mar 22, 2015 19:54:58 GMT
This is from the workshop manual and the plugs they should have .....
P125X....
Marelli CW 6N AT
Bosch W225 T1
Champion L86
NGK B7HS
AC 43F
PX125E.....
Marelli CW 6N
Bosch W 5A
Champion L 86
NGK B6HS
AC 43F
Hope this helps.
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Post by doulsy on Mar 22, 2015 20:36:16 GMT
This is from the workshop manual and the plugs they should have ..... P125X.... Marelli CW 6N AT Bosch W225 T1 Champion L86 NGK B7HS AC 43F PX125E..... Marelli CW 6N Bosch W 5A Champion L 86 NGK B6HS AC 43F Hope this helps. will get the b7 to be on the safe side, will keep the other plug for when my 200 is rebuilt. |
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Post by rab on Mar 22, 2015 20:47:15 GMT
There is 2 types of plug long reach and short reach I've never seen a vespa with short reach plug Infact only low cc bike I've seen with a short reach in 30 years was the omz b6 b7 b8 and so on are only the heat rating of the plug I'd say your scoot had the wrong plug in to start with if the new plug was too long it would have at the very least squashed the electrode on turn over.if you had it running it would have gone through the piston or smashed the plug and you would be stripping the head either way
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Post by doulsy on Mar 22, 2015 20:58:27 GMT
There is 2 types of plug long reach and short reach I've never seen a vespa with short reach plug Infact only low cc bike I've seen with a short reach in 30 years was the omz b6 b7 b8 and so on are only the heat rating of the plug I'd say your scoot had the wrong plug in to start with if the new plug was too long it would have at the very least squashed the electrode on turn over.if you had it running it would have gone through the piston or smashed the plug and you would be stripping the head either way ye recon i should put it back in Rab? it did make it easier kicking from cold. |
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Post by rab on Mar 22, 2015 21:09:22 GMT
1st to make sure someone has not changed the head look at the thread with a torch in the head you will see the thread lengh and weather its long or short. a short reach plug will run in a long reach socket but will run rough and you will get carbon build up on the head thread also just for info it may have changed but NGK heatranges run "backwards" compared to Bosch ie 6 on ngk is a hot plug and on bosh its cold. they could have nakerd the thread in the past and used a short reach plug so it stays in so double check the thread fro damage
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Post by doulsy on Mar 22, 2015 21:12:17 GMT
1st to make sure someone has not changed the head look at the thread with a torch in the head you will see the thread lengh and weather its long or short. a short reach plug will run in a long reach socket but will run rough and you will get carbon build up on the thread also just for info it may have changed but NGK heatranges run "backwards" compared to Bosch ie 6 on ngk is a hot plug and on bosh its cold right the last bit just confused me lol, will do the torch bit tomorrow cheers |
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Post by rab on Mar 22, 2015 21:14:04 GMT
slap a b6 or b7 if you do round town or b7 b8 if you do more open road riding
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Post by doulsy on Mar 22, 2015 21:30:30 GMT
slap a b6 or b7 if you do round town or b7 b8 if you do more open road riding only gonna ride for fun Rab, might do some 30 mile runs to the coast, be lucky if i will do a few hundred miles per year on it, i don't mind buying some spare plugs, hope to have the original engine back in next year anyway, will do the torch thing and stick that new plug in if it looks ok, cheers for the advice again |
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Post by doulsy on Mar 23, 2015 17:31:14 GMT
The thread on the head is same size as the small sparkplug, br7hs, so i was lucky the other plug never done any damage? When i press down on the kickstart i can see piston come up but not right to the top so i dont think it would of hit the longer plug.
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Post by vespasco on Mar 23, 2015 18:43:05 GMT
Nice one. Its never a good idea to use the wrong depth plug as it will ruin the threads on the plug and/or the head, as mentioned. The plug sits in a dome on the inside of the head so you were lucky  |
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Post by vespasco on Mar 23, 2015 21:05:58 GMT
You know better than that |
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Post by doulsy on Mar 23, 2015 22:00:55 GMT
so i just replace with the same plug i took out? maybe someone has built this engine from bits they had lying about, it sounds ok and goes so it should do for the summer anyways  |
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Post by henri on Mar 24, 2015 10:33:39 GMT
yes gaz ,a long reach plug does increase compression by taking up volume ,an vesps will run with em , was a dodge in tuning/racing circles years ago, problem is the plug end sits in a much hotter part of combustion chamber ,so you'd need a bh9 or there abouts an it will only last 1 race or sprint , it was the cause of many a holed piston til it went out of fashion , otherwise the 3-4 plugs on my shelf from when ive rushed halfords without my glasses would get used .
memorys kicking up a glimmer that there is a vespa with thicker head that uses long reach plugs , centre plug px200/t5 maybe , or 1 of the kits , but could be well wide of the mark there . H
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Post by vespasco on Mar 24, 2015 18:14:37 GMT
Use a plug that is the correct depth for your head.
I guesstimate a long reach plug in a short reach hole would give a lesser volume of about 0.3cc? You'd need a pretty highly tuned motor for that to make a lot difference.
Then, when the plug thread ends gets covered in carbon you cant get the plug out, or strip the threads in the head trying to.
Plus it would interupt the flow of the mix! Plus the heat being nearer to piston crown etc
200s are long reach.
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Post by henri on Mar 25, 2015 8:35:44 GMT
people use to fill pistons with allsorts of stuff ,to raise primary compression , kegra racing tried it , if the extra weight/momentum dont trash ya big/little ends ,the piston expands more than filler which then drops into cases =BANG,
an you could try ya fancy tune but would prob have to get a billet piston machined out of fancy ali to resist burn through , reckon all the pop bubbles have gone to ya brain , can you hear "fizzing" , H
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