14 years later; it's finally due for a top end.

TheLetterJ

TheLetterJ

New member
My '01 300 started making some "angry" noises as well as developing what I would call a lean surge while coming back down to idle near the end of my ride last weekend. The ride was entirely extremely tight and overgrown singletrack with big rocks and downed trees, temps in the high 80's-low 90's. The pipe was still tight at the flange with the bead of red RTV (I smeared some of it inside the pipe before sliding it over the exhaust flange/ o-rings) still intact so I pulled the pipe off to have a look in the cylinder. The cylinder walls looked burnt (brown streaks) and there was sticky gunk between the rings. I pulled the plug at the water pump and only ~1 cup of coolant came out... rut roh. I had given the bike its usual once over the day before including checking the coolant (which had not needed to be topped off at all since its last flush.) I blew steam a couple times during the ride, but not enough that I was concerned, I guess I should have been.

I had checked the topend out a few months ago (probably 170-180hrs then) when I replaced the pipe and all looked well, but I'm right around 200hrs now (I bought the bike ~3 years ago with the fuzzies still on the original tires) so I can't be mad that it needs its first piston... I'm sure it would have gone much longer if I hadn't blown all my coolant out! I was worried that I'd need a replate, but the cylinder cleaned up really good with some WD40 and a green Scotch Brite pad. My snap/bore gauge isn't big enough to accurately measure the cylinder for roundness/ taper, so I'll have my machinist measure it and then I'll know for sure if it's still good.

It's kind of ironic that this happened on the very first ride running a different 2T oil. I have been exclusively running Champion WP2 in all of my 2T's since about '03 but I finally ran out (I had been buying it 6 gallons at a time) and needed something for the weekend and figured 927 was a safe bet. I am not saying that this caused any of my issues, but I sure had a lot of spooge inside the powervalve cover and in the exhaust that I NEVER had before.

Oh well, I can't be upset, it's still the most reliable offroad bike I've ever owned and my favorite powerplant for tight terrain, it's totally worth putting money into. At least this is a good opportunity to finally have the head cut and a few other minor "upgrades" while I've got things apart. The only bummer is that I'm spread pretty thin right now so it will be a while before I can put any money towards fixing it.
 
I have an A cylinder, but assuming it doesn't need a replate I'll likely put in a B (or maybe even a C) piston anyway. The difference is only 0.01mm or 0.0004" and I'd call that acceptable wear even in a plated cylinder. I can't even measure that small. It does have a visible ring around the top of the cylinder but it is hard to feel it, I'm hoping I just need to spend more time with the scotch brite.
 
The concern about the ridge is to prevent the new top piston ring from getting stuck on it. You could either have the cylinder diamond honed to remove the ridge or add a little more base gasket so the piston does not hit the ridge.
 
I'm still too poor to do anything with the GG, but I was looking over the cylinder a bit closer today and noticed a lot of very tiny (~1/16") vertical lines (heat checking?) in the plating. They don't look like scratches as they are not continuous and I can't feel them at all, so I'm guessing that I overheated it enough that the cylinder expanded and the plating could not expand at the same rate? Either way, I think I'm going to have to replate it or I just won't trust it. Darnit!

On a related note, since I need a topend and replate anyway, do I have any options for a big bore on the 300? I'm not looking for anymore top end power per se, but more grunt off of idle is always a good thing in my books! Yes I'm one of those wierdos that enjoys trail riding CR500's :D
 
Wow, I didn't realize the GG has been down so long! I had my machinist measure out my old parts and inspect the plating and he said that it would clean up just fine with a diamond hone. The piston had very even wear and was worn .0015" from new.

I ordered a "C" sized Wossner piston and topend gasket set/ wrist pin bearing from Steve Beane at Plus One Performance and will have my cylinder honed on Monday.

As soon as I get the cylinder bolted down I will do a couple solder/ squish tests and send the head off to Ron Black.
 
I know, I know, I'm moving at a glacial pace. Ridiculous amounts of overtime at work, and now nursing a back injury means all I can do is occasionally peak into the garage and look at it.

Anyway, this bike has always been hard to start (referring to the amount of force needed on the kickstarter) even compared to riding buddies bigger 2T's (KTM 360/380, CR500, KX500.) I've noticed on a few photos of others' GG 300 rebuilds that there is a small bleed hole drilled above the exhaust port. I've seen this on other 2T's as well and I understand that it is there to act as a compression release of sorts but it's small enough to be insignificant at running engine speeds. The YZ kicker made a nice difference in ease of starting, but with 2 false hips, I'm always looking to make it easier!

My question is: do you think it is possible to drill said hole into my cylinder WITHOUT replating, or am I asking for trouble? Does anybody know the diameter of the hole and it's height relative to the exhaust port? Is it just at the top of the PV cavity on the opposite side?

Here is my cylinder, the pick is pointing to the approximate location of where I've seen the hole drilled on other bikes:



My machinist gave the cylinder a VERY light pass with the hone and said that it looked acceptable, but I'm still not 100% happy with it. What do you guys think? No chips, flakes, or gouges, but clearly it isn't perfectly smooth (not worried about the ridge where the ring stops as I'm raising my cylinder slightly anyway.)
 
And why do you want to drill holes in your plated clyinder??

I think it would chip and crack, then you're really screwed!
Ive seen pistons drilled for the exhaust bridge.......

if your looking for a big bore...call Eric Gore.....see what he can dream up or Eddie Sanders Racing......I think he's in your area......
 
It doesn't look good to me at all.
I don't like the look of the wear at the ports.

You can get away with a lot more with big bores though.
As far as top ridge goes you can use a thicker base gasket to get away from that.
Will also lower the compression a bit and make for an easier starting bike.
Probably won't be noticeable though.
Sounds like you want to mod the head so that puts you in a bad spot if you have to raise the barrel.

Everybody gets to this point with an older Gas Gas eventually.
Dumping a lot of money into an older bike with low resale values.
I think personally that's the wrong way to look at it.
The value is in what the bike means to you.

Hunt down a better cylinder.IMO
 
That's all the 2nd opinion I needed to decide to send the cylinder out for plating!... which brings me back to the "compression release" hole. I will have the head cut (which I know will raise the compression, making it even harder to start) once I get the cylinder back, I'm hoping that I can cancel out/ minimize the starting difficulty with the bleed hole.

Since messing up the plating won't be a factor, does anyone know the diameter and height of that hole?

Here's an image (from a different brand 300) showing the hole I'm talking about: http://www.dirtbikeworld.net/forum/showthread.php?p=1474944

Rick: I already have my Wossner "C" piston so the big bore is off the table now. ESR is right up the road from me and he no doubt knows a thing or 2 about big bore/ stroker 2T's. The drilled piston you are refering to is just to provide extra cooling/ lubrication to the narrow bridge between 2 exhaust ports (as commonly seen on 125's) and has nothing to do with compression release.

ggxc: It's a toy, resale value is of little concern. I like the bike and I refuse to buy a newer one just because of "red sticker" restrictions in CA, so it's totally worth fixing it. This bike has treated me right for over 200hrs and I'd like to do all that I can to make sure it will go 200+ more. If spending a few hundred more to plate the cylinder is what it takes, it's still much cheaper/ easier than having to replace the bottom end if the plating failed and took out the crank. I'm thinking that fixing this cylinder won't cost anymore than buying a "good" used one, and I'll end up with basically a brand new cylinder. I'll be off my bikes for at least the next few months, so I've got the time to make sure it's done right.

I know that an "A" piston would have been a better choice had I known I would be sending my cylinder out, but I was hoping the honing would have been enough to clean up my cylinder, hence the "C" piston. Does anyone here have a strong recommendation for who to use for plating? I was planning to use US Chrome unless somebody has a good reason that I shouldn't use them?
 
I didn't measure it, but eyeballed. Looks like a 3mm hole. It is chamfered on the plating side (didn't measure but maybe 5mm). 34mm to the centre of the hole to the top of the jug.

If you look in the exhaust port with the PV removed, the bleed is visible at the top middle/highest point. This gives you the most meat to drill through. Lower and you may find it compromises structural integrity. Higher and it won't bleed anywhere. Too high and you'll find the cooling system.
 
Perfect, thank you!

Without having it in front of me, I'm thinking I'll drill the hole from the outside in (which will have it at a slight angle) so I can do it in my drill press and try to maintain some sort of accuracy. As far as chamfering, I'll see what I can do by hand before breaking out the die grinder!

Thanks again Jakobi!
 
Baby steps!

I finally drilled the 3mm (well, 7/64"... close enough!) hole above the exhaust port. Surprisingly it didn't damage the plating, but that is neither here nor there because it's all boxed up and ready to be shipped to Powerseal in the morning!
 
if your in to your cr500 they do a mod on the head by adding a type of valve to enable easyer starting.

to be honest my bore was worse than yours I have just put a new piston in for now. the bike runs well and has loads of power
will get it plated next time tho, like you I was short of cash at the time

grant
 
I got my cylinder back (it sure is purdy!) so I installed the piston and the whole stack of base gaskets (0.95mm) and the piston is still ever so slightly covering the bottom of the transfer ports at BDC. The original stack was 0.65mm and while the bike pulled well from down low, it signed off VERY early. I guess I didn't realize how big of a pain in the butt it is to get an ACCURATE measurement there, but I think my goal is to have the piston flush with the transfers (not necessarily the exhaust port) at BDC. My thinking is that will give me the top end the bike has been lacking, and having the squish band modded/compression raised will at least keep the bottom end power the same as it was... if not give it a little bump too.

I'm going to make a list for any other bits and pieces I need (such as my water pump seals/impeller) along with another set of base gaskets before going any further.

I still can't ride so I would rather spend the time to get the GG setup PERFECT vs just getting running the same as it did before. I've got a '02 YZ265 with SSS suspension, WR tranny, etc, etc, that I'm prepping right now for a friend, so as usual, things will continue to happen slowly!
 
I received my 2nd set of base gaskets and have been playing with different stacks. At 1.3mm of gaskets, the transfers on the left side are perfectly flush with the top of the piston at BDC, the transfers on the right and the exhaust port are both covered ~.3mm still. The piston is slightly below the rear (boost?) port. I still have a .3mm and (2) .15mm base gaskets, but I think I'm just splitting hairs at this point and I'll be happy just leaving it at 1.3mm now.

I double checked my ring gap and it is ever so slightly tighter since the replate (go figure) at .012" which sounds perfect going by the .004" gap per 1" bore calculation.

I got all of the powervalve pieces cleaned up good as new (thank you Easy Off!) and noticed the larger of the 3 bearings had a crack in the shield so I'll just add all 3 bearings to my order, no need to rob them from my roller skates.

Next up is buying some solder and doing a couple squish tests.
 
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