350 inspection

[Huskybill]

On my 350 I checked the cylinder adapter base for flatness. Both sides seem to be warped with gaps between the securing screws on the crank right to left. The cylinder side was a tad gap wise too. I like the mating surfaces to be as flat and parallel to each other before assembly. Luckily I have a flat surface to check them on. I lapped both sides with 400 grit, then 600 grit, then 1,000 grit. It’s good to go now. A massive air leak that’s why we inspect, and do a leak down check after assembly. Don’t leave any stone unturned.

 

[Wood Doctor]

You could have uncovered why one of my 350s still seems to be hurting for compression and and has less power than my 353 or the other 350. They all have the same sized top end. I burnished it down prior to installation but did not check for total flatness. My error. It's showing 135 psi compresioon cold, but the other two are at 150 to 160. Needless to say, they both make it look rather weak.

 

[Huskybill]

Both ends were warped. The crank bearing side more.

 

[Huskitoter]

A high squish on an oem cyl would be a dead giveaway.

Other's have mentioned that the base screws on the early model had a tendency to loosen. Guess that is what allows the corners to warp over the years. The threads on the later model are different, so you may want to use them instead of the original screws.

 

[cuinrearview]

I don't even check them anymore, I just knock .010 off the top. It sets the squish about where it should be too with no base gasket.

 

[Huskybill]

Milling it doesn’t make it flat and parallel. It has to be lapped in on a flat surface to be perfectly flat.

I hope the milling head is trammed correctly.

 

[Huskybill]

the orginal one in the 350 was milled on the top while the bottom is casted. After carefully lapping in both sides on a flat surface it measures 1.333” no matter where I measure it. After some porting it’s good to go.

I just received a new one from huztl, it’s casted with no machine marks. After six measurements no two are the same. I started lapping it and it shows the pattern around the outside and inside square.

Just something to check. I don’t like to depend on yamabond to seal this to the case with gaps. The flatter it is the better the seal.

 

[cuinrearview]

Milling it doesn’t make it flat and parallel. It has to be lapped in on a flat surface to be perfectly flat.

I hope the milling head is trammed correctly.

It does if you indicate it first. This ain't a square and belt sander lol!

 

[Huskybill]

Try lapping it after you mill it.

I’m not talking squaring bar edges,

 

[cuinrearview]

Try lapping it after you mill it.

I’m not talking squaring bar edges,

Neither am I. I'm talking milling. On a Bridgeport. The finish is more than fine enough for a gasket or some YB4.

 

[Huskybill]

I’m not talking about the finish. I’m saying to try lapping it after milling it. It might still not flat.

 

[cuinrearview]

I’m not talking about the finish. I’m saying to try lapping it after milling it. It might still not flat.

I understand what you're saying. What I'm saying is in this application it is completely unnecessary. I've got one to do down the road, so maybe I'll take some pics and document it for you.

 

[cuinrearview]

I guess I should explain why I feel it's an unnecessary step. To truly make it worthwhile to get the top of the bearing cup flat you would also have to do the bottom of the jug. And the bottom of the bearing cup. And the plastic case. After all of that you're still squeezing down those bearings with the seal surrounding them, creating a way for the whole thing to be thrown off.

 

[Huskybill]

But how warped is the plastic lower case? I’m thinking by lapping the upper section, not really taking off lots of material by lapping just making it flat for a better seal.

The orginal used top cylinder adapter is more warped than the huztl new one.
The heat could be a factor.

Let’s say the securing bolt areas show up touching first when lapping. There’s a air gap between the bolt holes. We’re depending on sealant to fill the gap. This dirtbike sealant isn’t made to fill gaps. Dirtbike cases are flat and even with no gaps.

 

[cuinrearview]

But how warped is the plastic lower case?

Is "way warped" a thing? The layers of a 350 sandwich are pretty uneven. I think I screwed up by even mentioning "squaring up" the top of the bearing cup. I think i added it more to illustrate the "un-squareness" to begin with. I suspect even pro saw cases to the cylinder surface is a relatively (in this context) poor match. The gasket, and play in four axes at the piston pin makes up for it. But we want that there...

 

[sunfish]

Flat is good, but lapping to 1000 grit is completely unnecessary.

 

[cus_deluxe]

Flat is good, but lapping to 1000 grit is completely unnecessary.

Not to mention that it does nothing but increase likelihood of an air leak. If we are being technical, the finish left by milling or lathe work creates more sealing surface. People get all riled up about a thousandth or two....it’s a chainsaw not a friggin spaceship

 

[sunfish]

Not to mention that it does nothing but increase likelihood of an air leak. If we are being technical, the finish left by milling or lathe work creates more sealing surface. People get all riled up about a thousandth or two....it’s a chainsaw not a friggin spaceship

I agree.

 

[cuinrearview]

Not to mention that it does nothing but increase likelihood of an air leak. If we are being technical, the finish left by milling or lathe work creates more sealing surface. People get all riled up about a thousandth or two....it’s a chainsaw not a friggin spaceship

Yer fricken mom's riled up...

 

[cus_deluxe]

You're fricken mom's riled up...

LOL!