Monster Cag B1 help

[.bLanK] GoD · #1 (**permalink**) 02-11-2009, 04:44 PM

I'm building a B1 motor with more trick bits than you can shake a stick at.
It started as a cag motor that needed a water pump sorted which is not uncommon.
Some say I may have gone overboard, but meh it's only money.

Some of the bits I've done are:
39mm big bore top end
High compression head dome
Silver crank 39.2mm
Hi cool head
Port matched
Blata CF reeds, stuffer, manifold
19mm Dellorto, Clear float bowl
Blata race clutch
TecnoX open clutch housing
SPS auto cooling clutch drum
Blata water pump, pully, belt, flywheel
Blata ignition coil
Unifilter High flow air filter
New Gaskets, seals and bearings all round

What I would like to know is:
* Squish gap for the big bore cylinder + high compression head.
* Where the squish should be measured

The first thing I noticed the other day doing an initial squish measurement was, the piece of solder used to measure the squish came out a completely different shape Vs the normal head dome on my other B1 cag.

With the high comp head + big bore there is a little sharp ridge on the inside of the head. Imdying mentioned that that was a good spot for heat to build up and possibly cause detonation or just simply overheating problems. This is obviously because of the increase in bore diameter.

It was imdyings idea to stick the dome in the lathe and machine that little ridge smooth which I think is a good idea.
Once I machine that ridge back what sort of squish would I be looking at then?

I'm going to pay a visit to the gasket shop this week and get them to make me a 2mm copper base gasket.

rover · #2 (**permalink**) 02-11-2009, 05:57 PM

Hi Blank God
I think that you may have a head from a 39cc kit...thats not good at all, what you have shown and Imdying has hit the nail on the head...picture when combustion occurs where the explosion goes...down the side of the piston putting more force on the rings than it should..not on the top as it should be.

Dazza · #3 (**permalink**) 02-11-2009, 06:25 PM

I agree with Rover, looks like a 39cc dome.
You may have trouble with the sealing of the dome, as the flat lip is very close to the seal and may melt it.

I would say, take the dome out and make a new one with the seal further over if possible.

[.bLanK] GoD · #4 (**permalink**) 02-11-2009, 06:56 PM

Arrh so the 39mm barrel has a different head dome. That makes sense.
This head dome came with the hi cool head.
I'll go hunting for a big bore head.

SpyGuy · #5 (**permalink**) 03-11-2009, 08:19 AM

Wow, nice engine. I'm digging that open clutch bracket ....

rover · #6 (**permalink**) 04-11-2009, 12:22 AM

Hi Blank God
Go to Pocket bike parts .com.au.....He sells the big bore kits and is a sponser on this forum.
The Guys Name is Ayden...Very reliable supplier

[.bLanK] GoD · #7 (**permalink**) 04-11-2009, 06:45 AM

Yep cheers, I emailed Ayden 2 days ago, got a reply yesterday. He does have some big bore domes. $10 aud.
Will get him to stick it in the post b4 the end of the week.
I have got stuff from Ayden before, he is pretty onto it.
He also states on his shopping site that his B1 big bore kits have the piston with the ring gap locating pin in the right place. Not easy to find.

[.bLanK] GoD · #8 (**permalink**) 27-12-2009, 01:55 PM

I have the proper 39.5mm dome now and the 2mm Cu base spacer gasket.
My problem now is I keep blowing the head O-ring after a few seconds of heavy load on the motor.
To rule out too high compression I spaced the barrel out another 0.8mm ish (no luck. I'll leave the squish there for now till I sort this problem).
Last night I;
Replaced the dome O-ring with Viton 1.5mm (was previously using 1.78mm)
Found the rear engine mount not fully tight, corrected that with a SS washer to fill the gap.
Installed the dome into the original head.

Last time I rode it and blew the O-ring I noticed after warming it up the water level in the expansion tank had risen from just covering the bottom of the tank to nearly full. I thought that a bit strange so I shut it down, let it cool a bit before checking the coolant pipes were properly bled. Found the head had a huge air pocket in it. I thought I had bled it properly so I did it again. We definatly had it bled properly then, but it still blew the O-ring. Not sure if the Hi cool head has anything to do with the problem but that's why I have gone back to the standard head for now to try and eliminate that.

Going for a fang today, fingers crossed.

[.bLanK] GoD · #9 (**permalink**) 28-12-2009, 04:46 PM

So yesterdays run was fairly successful. The head O-ring didn't blow out this time.
Carbon forks feel nice and solid, PMT's are a dream to ride on, Grimeca hydraulic brakes are strong.
I Glanced down at the brake disc at one stage and saw the disc wobbling, found the bolts holding the disc on had come loose, dam glad i saw that before anything fell off and jammed the front wheel.
Next on the list is to raise the compression back to normal, fit the fairing and spend some time in tuning the carburetor.

Grevs · #10 (**permalink**) 28-12-2009, 10:41 PM

motor looks awsome , bike sounds as if its comming along great man. keep the posts comming about it.

Monster Cag B1 help

Posted in Pocket Bikes Performance Tips