New Slant Heads for 80cc's: Compression Boost!?

I'm a little new to performance 2 stroke theory. I ordered the slant head and got to wondering if indexing the plugs in these would be of any advantage at all.
 
I've got a Grube GT4 66cc and my squish went negative ;) The piston actually hit the head and the thing wouldn't even turn over. Luckily I didn't try too hard. I'll add the second head gasket that came with the kit tomorrow and try again. Just an FYI!
 
Did you try using more than one cyl base gasket

Ardilla_Loca said:
I've got a Grube GT4 66cc and my squish went negative ;) The piston actually hit the head and the thing wouldn't even turn over. Luckily I didn't try too hard. I'll add the second head gasket that came with the kit tomorrow and try again. Just an FYI!
Click to expand...
 
I've got one home-made gasket under the cylinder (the original disintegrated upon disassembly). It is made from auto gasket material. The head has one metal head gasket that came with the kit. I have one more metal head gasket at home. I'll probably try the 2nd head gasket 1st just because it's easier.

I'll stick a long piece of solder in through the spark plug hole and turn the engine over to check the gap between the head and the piston.

Does anyone know the proper deck height for this engine (probably a dumb question as these are slapped together). In fact I don't know if anyone has really mapped one of these engines.

Here's a cool 2 stroke excel spreadsheet that can be used to determine carb size, estimated HP, play with theoretical timing, port size etc. if anyone wants to take a stab at it.
 

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I just got mine and painted it black.

Took 10 days to get here. Anyway, only thing Im waiting on now is the new head gasket from SBP.

New question after reading the above problem.

The only gasket that I should need is the new thin metal one from SBP, correct? Or do I need a paper gasket, like the one on the exhaust, as well?
 
i wouldnt waste my time measuring the 'squish' it verys so much in these motors its not funny (well maybe a little). As for the measurement should be... if it dont hit, I wouldnt worry unless you push it real hard (10000+rpm) then if the rod stretches enough to cause contact with the head then you may consider adding another gasket...
Theycallmebob: you may need another base gasket or more than one of the head gaskets to allow enough space. What I would do is install the new head with the old head gasket and if it hits then buy another head gasket or base gasket so you will have more space that way you wont ruin your new SBP head gasket...
 
I have not had the time to ride for a few days.....before I mess with the carb/jets I'm going to take the BP5HS out and try a B6HS, just to see....
 
So I just zipped around with the B6HS. It actually runs much better. Strange how just close to the edge it is, and the hi-perf hotter plug puts it over the limit. This is all with regular gasoline and racing oil/castor mixed about 25:1.
 
Two head gaskets worked. I checked the clearance with a piece of solder and have adequate clearance. I'll check for leakage around the head but so far so good.

I'm still running the stock plug. Gotta get a new one. You're not running the long one right Pablo?
 
I got mine and got my SBP gasket slapped it on, and I have a leak around the gasket. I torqued the bolts down to 15ft/lbs.

I tried the stock gasket that was not leaking before and it was leaking too. Do I need to apply some gasket sealer when I install the head gasket?
 
Does sound like something isn't flat. Have you rode it a few times, cooled, torqued and heat cycled and torqued it again?

You can try the aluminum paint trick.
 
Pablo said:
Does sound like something isn't flat. Have you rode it a few times, cooled, torqued and heat cycled and torqued it again?

You can try the aluminum paint trick.
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No, I really have no experience installing a head gasket. Is it expected to leak a bit until then? Heat cycled is the only term I am unfamiliar with above.

The symptoms which lead me to believe it is leaking are:

-Less power than before the new head
-Loud noise coming from the head under acceleration
-The SBP exhaust is much more quiet than before, like not as much air is being pushed through it
-On the left side of the engine I can see a small amount of oil leaking from between the gasket and the cylinder head.
-Lots more smoke than usual

Sound about right?
 
theycallmebob said:
No, I really have no experience installing a head gasket. Is it expected to leak a bit until then? Heat cycled is the only term I am unfamiliar with above.

The symptoms which lead me to believe it is leaking are:

-Less power than before the new head
-Loud noise coming from the head under acceleration
-The SBP exhaust is much more quiet than before, like not as much air is being pushed through it
-On the left side of the engine I can see a small amount of oil leaking from between the gasket and the cylinder head.
-Lots more smoke than usual

Sound about right?
Click to expand...

NO it shouldn't leak. But it can take a few heat cycles before it seals up. What I mean by heat cycles are as I wrote. Install gasket, torque, ride, cool, re-torque, ride, cool, re-torque. About the 3rd or 4th time nuts will remain torqued. Try this.

1) Less power could indicate a leak.
2) Noise could indicate a leak. (but make sure the piston is not contacting the head)
3) Gooze escaping, for sure a leak.

We never had a gasket fail, but we would be more than happy to send you a new gasket, but you'll need to make sure the head is flat, not gouged, etc....

Are you familiar with Aluminum filled paint?
 
Not familiar with the paint.

I dont think the piston is contacting the head, when I took off the SBP gasket and replaced it with the old one I looked at the dome in the head, and it seemed untouched.

Perhaps the head isn't flat. What should I do? Take it to a machine shop?
 
Low cost (or good) stuff Al paint is pretty cool (Norman trick) just coat the gasket pretty wet and assemble ( a bit messy so use nitrile gloves if you have them). It will take care of minor irregularities. Seals really well. You can also hang the gasket to dry before assembly, but I'm not sure that works as well (never tried it)

You can at least check the head with a metal straight edge or a square.
 
I bought the sex version at Tacoma Screw. (I'm sure Grainger/Fastenal has it too). But Wally may have a low cost version and Home Despot and Lower's may have it as well.
 
You can tell if it's hitting pretty easily if you take the spark plug out and roll the bike with the clutch out. You probably will hear it. Put you hand on the head (as long as it's cool) and you can feel it. Lastly you can get a long piece of relatively thick solder and put in in the spark plug hole against the cylinder wall. Roll the bike to turn the motor over once or twice. Take the solder out and measure the thickness of the squished part.
 
Doggummit - my slant head started leaking too!!

I took it all apart, cleaned it, soaked a new gasket with aluminum spray paint, re-assembled and torqued it to 17 ft. lbs. Then I said "OH KRUD - I forgot to check it for flatness!!!"

I'll take it for a ride in a little bit.
 
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