Engine Opinions

is the cluch dragging ? ed

Dad's out of hospital, still not fully recovered, would Im sure welcome a visit from you or Malcom.

talk soon

Hi Derek,

If you mean its not releasing properly then yes, taking it apart yet again as we speak. Yes dad said he is out, they had a small chat on the phone yesterday.



Eddie

Well we have rebuilt the clutch again and cleaned a few parts as per alans helpful advice on sunday. Have managed to keep hold of the roller starter so will try again and see what happens.


Eddie

Well yet again frustration has taken over from enthusiasm, spark there, fuel there, take plug out and turning over fine, plug back in and very very hard to turn over even with a starter to the point of flattening the battery.


At a complete loss.



Eddie

Sounds daft -- but it happened to me ...!!

When the surgeon´s assistants put swabs in the cut -- they count them and then when closing up they count them to make sure they are all out -- yet 18months after an op on my guts (in Kenya) a swab made its way out in what was looking like a boil ....

Sorry! (how could I be so insulting??) -- you could NOT possibly have a piece of rag near the carb or a very thin piece of material that could have fallen near the carb during your taking out of the plug and putting it back in to then get sucked in at your next start attempt ????

Sorry -- sounds insulting I know -- but with my Enfield Bullet scrambler a piece of thin nylon material, small as a post card,-- with a logo advert -- fell off the saddle and got sucked in, stopped the engine and was so trapped between the piston and cylinder wall the engine was seized solid.

Maybe I should delete the above -- if I knew how!!??

Hope there´s no damage, Ed -- Cheers!

Edward,
You must have way too much compression, better reduce it quick! even a high ish compression engine should be able to turn over fairly well.
Check the volume of the head to the top of the plug thread and let us know, we can advise.
Best compression ratio should be in the region of 12:1
Alan

Hi John & Alan,

Its not seizing john as without the plug in we can spin it fine so agree with alan as we though it has way too much compression as the other one i checked i can turn by hand, im sure we were told it is 12:1 but dad is working at home today checking it so will get him to measure it again.


Eddie

Head it a GT100B, dad says the notes written with it says it is 12.5:1 but we are going to check it tonight.

Eddie

Hopefully the head has been modified to suit a 175 motor and is still not set up for a 125! in which case your compression really will be too high!
Cheers,
Alan

Where are you measuring from, as clearance volume? From the exhaust port closure to TDC should be the swept-volume you use in the CR calculation....

Also -- have you checked the squish clearance? Piston crown to cylinder head clearance??

Formula is SSV + CSV / CSV .

-- where `SSV´ is swept-stroke-volume (with 2-stroke engines, from exhaust port closure to TDC) and
`CSV´ is Combustion Space volume including Bump Clearance (gap -- piston crown to head...) volume.

Hi Alan,


well it certainly has high compression so maybe it is something like that.


John,

i have no idea as dad usually does those bits.



Eddie

We ran Icarus-1 with a "Bump Clearance" of 30 thou"... Most were at 40thou" (1mm) I think and some at 20thou". When things get warmed up with the latter bump clearance the piston could be contacting the cylinder head!

Bump Clearance is the distance between piston crown and cylinder head. We measured it using Electrician´s very softcore solder of 1.5mm diametre . With the piston just a short way down the bore we put four pieces of this soft solder diametrically across the piston crown surface, refitted the head at its correct bolt torque and rotated the crank past TDC -- just once. We removed the head to find the four pieces of soft solder had squashed to a flatness thinner than original and measured (with micrometer) across these flattened surfaces. Getting the clearance equal -- side to side, front to back -- meant some machining of the cylinder head...
Can be a painstaking job to get the clearance exactly at what you want -- particularly with the domed piston crown.

Maybe you knew this already Ed -- but I have a feeling your Bump Clearance MIGHT be part of your difficulty...

Cheers!

This one is a mystery and I took a look back at the previous posts on this and came across that you are using a long-reach plug in a short reach hole, Ed! -- Hmmm!? Would only mean about 1.5ccs in the combustion chamber -- unless you used lots of plug washers...? -- and that 1.5ccs would not make that much difference -- would it???
Cheers!
I.M.B.Wilded.

Hi John,

As far as i know its a short reach plug and we dont use any washers with it, even with the exhaust off it is very very hard to turn with a plug in, even put a standard d14 head on and still the same.


Eddie

Sorry Ed!
I am totally lost.
You say that without the plug in the engine turns freely -- but when the plug is in the engine needs a lot of effort to rotate ...?
Is it only when the piston is coming up on compression that it gets hard to turn?

What did the top surface of the piston look like when you took off the head?
Was there a lot of oil around the outer edges of the piston crown...?

I am about to give up....! Besides, I have just been requested to do something USEFUL!

O.L.D. Hat!

Yes john, without the plug it turns over almost the same as a normal bantam as i have checked, once the plug is on then is is very hard to turn regardless of coming up on compression. There is a picture of the piston as it is in this topic, no there wasnt alot of oil around the piston crown. Have also noticed it gets difficult once you tighten the head down, not sure if that is relevant.


Will put it in the line up tomorrow to try and get started and see what happens.



Eddie

What you said last -- when the head is tightened down it gets harder to turn...

Oooh oh! Natsy thought! A remote possibility is that the con-rod is bent -- hence the piston is forced against one side of the barrel when the head is tightened down -- which of course would tighten the barrel down square --

-- or, when you have the barrel off is there side-to-side movement of the piston on its gudgeon pin? If one edge of the conn-rod, at the small-end is pushing against the piston´s gudgeon-pin boss it will cause the piston to rub hard against the the cylinder wall -- when everything is tightened down...

-- or? No! this notion is really stupid...

... is there something under the barrel base causing it to be lopsided?

If either of these is the cause one side of the piston will be polished or scored...
Putting marking blue -- or even Tippex (typists white stuff for covering up mistakes) on the sides, re-assembling and rotating will surely show signs...???

Must go -- I am being watched and timed...!

I hope I am wrong about the conn-rod being bent!

Cheers!

B. Wildered.

Hi John,


Well we have checked everything else so will check what you have mentioned in the morning and see what we find.



Kind Regards

Eddie

Well after taking the head of and on again and the same with the barrel, taking the piston out, adding gaskets, taking gaskets off she has finally run! Had to put it into top gear to get it to start and cover half the air intake. Think some fettling with the carb is in order.......


Eddie

Not to try anything easy, it is a tt carb with a power/boost jet.



Eddie

Good Morning All,

From having a quick look at the carb the needle would appear to be on the middle notch, 109 needle jet and 200 main jet.


Eddie

I hope you´ve got understanding neighbours Ed!? quite a lot of smoke
not to mention the noise!!
Keep at it Young Man!
Cheers!
JayBee.

Hi John,


One set was out and the otherside are good people and bikers, lucky for them i had a clutch problem with one (not a bantam) and i didnt have a battery for the unsilenced bantam.

Yeah it did smoke alot but that may of been oil collection, plus the needle clip had stuck in the spring, it ran alot better than that afterwards and would rev up but the noise police intervened (Dad)!


Kind Regards


Eddie

Are we going to see that beastie out at Mallory or Cadwell?
It looks well! hope you can get it running sweet...
Alan