Major Gappage

[Baconator101]

A 66cc motor I've been using for a while, I found out out has a huge gap at top dead center. The Space between the highest point of piston to being flush with top of the sleeve is about 5mm. Every other motor I've opened, the cylinder sits to just about flush or sometimes a little protruding from the dome at top. At this point, this motor has been running so well that I will not be doing anything. I just wanted to see if any one else has encountered a situation like this.

 

[crassius]

I've seen whole bunches of slightly diff cylinders - I have a lot of good used cylinders here, but customer needs to bring old one in for measuring before I'll sell one.

 

[Baconator101]

I've seen whole bunches of slightly diff cylinders - I have a lot of good used cylinders here, but customer needs to bring old one in for measuring before I'll sell one.

I screwed that post up. It's edited now. What I meant was the piston at its highest point doesn't come close to the top of the sleeve. I could probably stick the longest plug in there, and not have to worry about causing harm.

 

[Tyler6357]

I'm interested in knowing what kind of engine you have? Is it a GT-5 or PK80 or something else? Does it use the piston with the low wrist pin location or the one with the wrist pin in the middle of the piston? I'm pretty sure that the ones with the wrist pin in the middle have a bigger squish gap.

 

[Baconator101]

I'm interested in knowing what kind of engine you have? Is it a GT-5 or PK80 or something else? Does it use the piston with the low wrist pin location or the one with the wrist pin in the middle of the piston? I'm pretty sure that the ones with the wrist pin in the middle have a bigger squish gap.

It's some cheap eBay motor, but it really has proved itself. The couple times I opened the top to look inside (aka fix what's not broken and secure the studs with loctite.) I could not for the life of me, separate the cylinder from the base. Whoever put it together must have used some type of sealant or something. I have opened up others cause I like to tighten up the studs before any usage and I have to be extra careful the sleeve doesn't slide up out of the base. But not this one. It will not budge. Could I pry it open? Ofcourse I could but I really have no reason to. When it breaks (hopefully not soon) I will enjoy breaking it down and seeing what parts are in it. But yeah like I said, that space up top is huuuge. But since I've used it so much and it runs so well (knock on wood) I will continue to let it be.

 

[crassius]

some cylinders have different deck heights - that is the distance between the base gasket seat and the head gasket seat - usually only about 2mm diff in height - some were meant for very thick base gaskets (some for two very thick gaskets), some for very thin gaskets

if it runs good, leave it alone

 

[Tyler6357]

One alteration some people have done to try to get more top end is to raise the cylinder by putting a second base gasket on. Doing this will increase the transfer port and exhaust port timing. Doing this will also increase the squish gap. However, raising the cylinder up will retard the intake timing. To correct this a 2 mm groove on the side of the skirt of the piston must be cut out.

 

[Frankenstein]

Some gaskets are like that, they just really cement themselves together, the intake gasket on the bt is somehow stuck to the actual intake bad enough that only a razorblade was able to peel it off and that itself felt like cutting through a piece of leather. The original base gasket was half glued to the case and the other half to the cylinder which is how I tore it on the first attempt at separating.

 

[crassius]

I always soak gaskets in oil before installing - keeps them from drying out or sticking and helps them seal better on uneven surfaces.

 

[FurryOnTheInside]

I always soak gaskets in oil before installing - keeps them from drying out or sticking and helps them seal better on uneven surfaces.

When you say "soak" do you mean just coat in oil and tighten everything down immediately?
I tried soaking a gasket for a couple of minutes while I was doing something else and it took longer than expected. The gasket swelled up (thickened) but it also lengthened and softened considerably.

The next one I'm trying is a thin base gasket, looks like just cardboard rather than the fibre type. I will try to just drop some oil on from a syringe as it is being assembled so it doesn't have more than a few seconds to soak in before the gasket is compressed.