blueprinting not hotrodding

N

nolan_speed

New Member
Well I was working on the bike yesterday and remounted the engine. I bought it already put together and the motor was spaced away from the frame and the mounts broke. Not it's mounted properly on the frame. But once the motor was re mounted, I did a little bit of work to it. I had the carb off of the motor for adjustment and when I looked down the intake and I noticed that there was some casting junk at the bend, obviously restricting flow, so I took off the intake and noticed that the intake is round and the port in the cylinder is square which doesn't look right. Anyways, I removed all the casting flash with a die grinder, smoothed the bend in the intake, and then port matched the intake to the cylinder and smoothed the transition as much as possible. I also removed one of the two head gaskets (are the slant heads supposed to have two for some reason?)

After I got the engine back together it ran so much better! Of course the top end improved but the main thing that impressed me was the increased torque at lower rpm and it's improved hill climbing ability. I figured that none of these things are really hotrodding but rather just outing the engine together the way it's meant to be. They aren't designed to have crap in the intake restricting flow, or to have mismatched ports and I doubt they're supposed to have two head gaskets, so those couple items really makes the motor run much better and I encourage anyone else to make the same improvements.
 
i agree. new motors i install, i match the ports, lap the head, remove all casting flash, clean up the transfer ports in the case and the jug, and basically blueprint them.

i've done it enough so i know what works for the motors i have, and haven't bothered with trimming piston skirts or drilling holes in the carb, rejetting, or whatever irreversable, potentially damaging mods that other people are so keen on, and all my bikes run smooth, mostly vibration free, and i'll put them up against anyone else's "hotrodded" bikes anyday.
 
Nolan Speed, I have the slanthead 80 (66) and I also have the 2 aluminum headgaskets on mine. I suspect they're supposed to have 2 gaskets for clearance purposes to make sure the top of the piston (dome shaped on mine, not a flat top) doesn't hit the sparkplug at TDC. However, I haven't tried removing one or both of the gaskets to test this interference theory. It's just an educated guess.
 
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I pulled both gaskets off then set the head back on the cylinder (but didn't bolt it down) and spun the engine over a few times and nothing made contact. I put just one of the gaskets back on and it runs much better now with a little more compression. Stock I think they only have like 6:1 or something which is super low, a little more compression shouldn't hurt anything.
 
You're right, a little extra compression won't hurt. Good to hear that there's no contact in your engine. I might try removing a gasket myself. But I'll do some testing first. Since thousands of an inch make all the difference here and the machining on these engines not so wonderful there's also the stretching of the rod or the slack/tolerances in the bearings being changed (slack being taken up) at the point when the piston with all its inertia hits TDC. There might be no contact when the engine is just turned over by hand but contact when it's actually running. Best and simple thing to do is use a piece of plasticene/playdoh (heck even bubble gum will work LOL) and see just how much room you have at TDC between the plug and the top of the piston.

Also a lot depends on the plug you use and how far it protrudes into the combustion chamber. Another thing is the orientation of your spark plug's ground electrode when it's tightened in the slanthead. Depends on how the threads were cut at the factory and how tight you tighten your plug sometimes the ground elctrode might be sticking out at the top closer to the roof of the head's combustion chamber (so no contact), sometimes it might be sideways (no contact) and sometimes it might be closer to the piston (contact) and cause interference with the piston on engines where the piston top comes very close to the roof of the combustion chamber.
 
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What you did is port and gasket match. (as you said)

Blueprinting is where you check and adjust all the internal clarences to specs.

(eg: bearing clearences, piston ring-gap)

I recommend everyone port/gasket match.
All the motors installs and complete bikes I'm selling come with that done for free.
 
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i agree with the above definition, but who knows what these engine's tolerances are supposed to be anyway?:)

i agree about port/gasket matching, as well as de-burring, smoothing, and cleaning out all the trash/metal chips.

and case in point, i just installed a brand new, never run, grubee starfire gt4 that i cleaned up, and it's doing 40+ on it's first run, with no four stroking, no hesitation, no bog, no nothing. smooth as glass...

running it full throttle right off the bat with 100:1 Opti2.

break-in time is for the birds...
 
bairdco said:
i agree with the above definition, but who knows what these engine's tolerances are supposed to be anyway?:)...
Click to expand...

I agree as well. Aside from port matching, cleaning up and deburring the 'rough edges' true blueprinting these engines is a bit of a moot point.

As for what the ideal torelances are supposed to be I guess the only thing you could do is see what the ideal tolerances in other good quality 2 strokes (Morini, Honda etc?) of comparable size typically are and use that as a benchmark. But by the time you go to all that trouble machining, fitting, etc you might as well get a better quaility 2 stroker to start with.
 
meowy84 said:
But by the time you go to all that trouble machining, fitting, etc you might as well get a better quaility 2 stroker to start with.
Click to expand...

I agree and I realize that I didn't do a full blueprint, there isn't much of a point in tearing apart the bottom end until there is a problem, it is a $160 engine anyways, run it till it blows. I just figured the engine wasn't designed to have two head gaskets and I know about checking clearances with putty and all that, but I figured that if nothing made contact with no head gasket and the engine cold then the the engine would be fine with the one .028" gasket.

I do have some experience with blueprinting engines, I have a 65 mustang that I built a nice little 302 for and I spent plenty of time checking all the clearances during assembly. But not much point on these engines, if you're worried about reliability, it makes much more sense to buy a quality engine than to truly blueprint these things.
 
nolan_speed said:
I pulled both gaskets off then set the head back on the cylinder (but didn't bolt it down) and spun the engine over a few times and nothing made contact. I put just one of the gaskets back on and it runs much better now with a little more compression. Stock I think they only have like 6:1 or something which is super low, a little more compression shouldn't hurt anything.
Click to expand...

My slant head was delivered with a spare head gasket also. It is my belief that the second one is provided should you want or need to flip the spark plug orientation. According to what I learned eons ago in the '70s during my dirtbike days, you should never re-use a head gasket! It appears that someone did the head flip on your motor and didn't remove the old head gasket. If you DO use 2 head gaskets you should "glue" them together with a product called Copper Coat which is a heat resistant head gasket adhesive that comes in a spray can.
 
I don't know which way the head originally comes installed but the spark plug was pointed forward when I got it and it fits fine with just the one gasket. Most cars have head gaskets that are laminated and have some type of printed silicone or similar sealant on them and they can't be reused. These are just aluminum and you can usually re-use them a few times. I hit both sides real quick with "chrome" aluminum spray paint and it seams to be sealed fine. On a liquid cooled 4 stroke engine a leaking head gasket is bad news as it lets the coolant and oil mix, but on an air cooled 2 stroke it isn't a big deal and I figured it would be worth a shot to reuse it and it works fine.
 
Mine was delivered with the plug pointing aft. I will flip it before I start it. My old yamahas had a head gasket with a rolled ridge in the center which got squished on torqing the head. These flat metal gaskets are probably fine for a couple re-uses like you say. I responded to this thread before i saw your post regarding your 302 rebuild and was trying to help a noob, which you are obviously not. I've had personal experience with the reality of a blown automobile head gasket a couple times. It's not pretty. Good Luck and Welcome!
 
there are some motors that come with two head gaskets installed. PK's are one of the brands. i was arguing with someone before about that. if you need to use 2 head gaskets to keep the piston from hitting, that's just a poor design. why wouldn't they machine the head flange larger, or make a thicker gasket? to me, coming like that from the factory is pretty lame.

also, almost all kits come with a spare.

i've re-used them plenty of times with no problems. i probably took the head off one of my motors 10 times, and the gasket still held up.

as long as your careful removing it and re-installing it, and you check it for deformation, cracks, dings, whatever, it should be ok.

if it was any other kinda motor, i'd replace it everytime, but it's not. it's the definition of low-tech. so low-tech in fact, that i've heard of people using aluminum paint and no gasket, and the d amn things still run...
 
My PK came just like Nolan_speed's with the head installed so the plug points forward (towards the exhaust). Honestly I don't think it would make much of a difference which way the plug points, except that if you point it forward and mount your little black box on the front tube your plug wire can be shorter than if you pointed it towards the back (towards the carb).

As for the 2 head gaskets after Bairdco's comment I'm starting to reconsider. Why not just have one thicker gasket or mill the head or case deck less at the factory to have a thinner gasket like he says. Makes sense. That second gasket could very well be a spare. I'll do the putty test and if all is well with plug clearance I'll probably end up using just one as well when I install my engine.
 
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if it was a spare, they'd come from the factory sealed in a bag, not attached to the engine..

as far as slant head orientation, it really doesn't matter. technically, it should be so the plug is pointing towards the intake port, so it fires quicker.

i think a lot of people use them because of clearance issues, so they can rotate it whichever way so the plug fits into the frame.
 
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