Im telling you with copper coat on it its less likely to leak than a fresh one. It will be a bitch to remove.
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Im telling you with copper coat on it its less likely to leak than a fresh one. It will be a bitch to remove.
The first few times we did it with great success. POS old mullet boat motor only had 70psi, ran perfect but had no punch down low. We cut the heads 3-4 times till compression was ~140psi and it felt like a new motor. The last time we reused the head gasket it let water in and scuffed one. $250.00 motor so it got a litttle muratic, a quick hone, a brand-new-used piston and we were back on the lake later that day. Pulled it off running when we built a fresh powerhead.
I gotta retract my statement on those thin gaskets. I checked squish this morning and its still at .054 and I figured out why.
I noticed when I took those gaskets that measured a little thin off there was a lot of oil around the metal ring. Didnt think much of it, figured just got it when I pulled them off.
When I was measuring the thickness of the different gaskets, I was measuring the crushed ring. I re-measured my crushed oem and pro gaskets and they measure .054 at the ring or the crushed fiber.
I pulled a head back off and measured the fiber on the "thinner" gaskets and got .054. Measured the ring and got .046-.48. Looked close and the ring had never crushed. Still had virgin clear sealer. It wasn't thick enough from get go. Thats why they accumulated oil around them. YIKES! The ring wasnt sealing a damn thing.
Lesson learned. Put a set of fresh Yamaha OEM gaskets in it and compression is the same. If you come across a set of those gaskets with the goofy ring thats wider on one side of the gasket than the other, I would not use them.
For anyone reading who is going to cut a set of heads, these are 115 heads marked 6E5
Cutting them down .050 will get you 140 psi.
Cutting them down .066 will get you 150 psi and you probably cant go much more without CC'ing them and figuring out the ratio then recutting the angled squish band until your where you want to be.
Like Baja mentioned at that point you might as well lose the gasket and oring them. You could pick up the .054 thickness of the gasket without cutting the head. Just off the top of my head, I think if you orung a stock uncut head you would fall in that 145psi range with a nice wide squish band that followed the dome. I can get a stock 6E5 head and next time I have my heads off Ill bolt one up with no gasket and some sealer and see what the compression/squish is.
If I was going the oring route and had the motor all apart. I would oring the block with a slight receiver groove in the head. I would also put a slight groove around all the water passages for the sealant to form a little oring when it torqued down.
Anyone ever try drilling a small hole in the throttle plates for idle quality?
I have my plates really closed down because I have my base timing turned up. With the plates just barely cracked, any tiny difference top tp bottom causes a rough idle.
Ive thought about putting a small hole at the top probably inline with the line of idle fuel ports and then closing the plates completely. That way the sync would be perfect with the plates closed and I could get the base timing up for better holeshot.
They way I am now I can get my base timing to about 15 degrees but getting the sync right is almost impossible.
Also will try and get a comparison for the 115 vs 130 exhaust chest plate soon. Hopefully before the Suwanee run.
Used to do it all the time when worked on performance 4 stroke stuff. Guys would get cams with to much overlap in them and to get them to idle, automatic trans car the worst, would be on the transfer circuit. Drilling the throtle plate would allow the plates to close enough to get them off the transfer cirçuit. Some cars gained 5" of vacuum at idle also took the lump out of the idle.
Never tried it with a 2 stroke, some advice, drill the hole on the top side of the throttle plate away from where the vacuum pulls fuel signal. Go in 1/16" increments, its amazing how small a hole makes a huge diff.
Dave
I was going to look at a Merc carb and see what size hole they use. The bore is the same at 3.5" so it should be similar. Start a little smaller and see how far I can turn up my base timing.
Start a 1 1/6" and go from there. Trust me been here done that.
Dave
The best way to set up throttle plates is to start with the carbs off, or in this case the one with the idle screw. Adjust the plates so the 1st progression port is just going to open. It needs to be covered for idle but needs to open with the slightest movement.
Now mount the carbs and run the engine.
If idle speed is too slow, drill hole(s) as needed to get the speed desired. The holes should be opposite the progression ports.
If the idle speed is too high, close the plates as needed, then pull the carbs and thin the plate with a file at the port so the port is just ready to open.
Back on O-ring heads, I just bolted a set of heads on my Excel engine with a bit of clay top & bottom on the piston. Not sure of precision on my first pass since this clay has firmed up a bit over the decades.
I get 0.018 to 0.023" clearance on a few pistons.
Chris you are working with squish numbers two to 3 times that. On the race car engines I work with we run squish down below 0.025" Commonly well below 0.020 on similar piston diameters.
What is it with these engines that calls for 0.070ish squish?
Got me? My understanding is mid .03's is getting pretty risky. So you would have to increase the squish if you just went with orings but thats the only way you're going to get less than .054 of the gasket without a custom gasket.
The mid 0.030s were what I grew up learning on bikes, cars everything. Once I learned to not read books and to read what the engine told me I found quite a bit of difference in a build. If the Gurus say 0.030 then I respect that. If that is a general number thrown out there I will build tighter.
In the engines I build tight there are no deposits in the squish area, granted these have been 4 strokes which to me are more critical due to the unloaded stroke where a 2 stroke is loaded every revolution.
If I were to do it again I would shoot for .045 (plenty safe) and match the curve of the squish band to the curve of the piston top with a 1 degree increase toward the plug. Im not an engine builder or designer but from reading that 1 degree and .045 are pretty good.
Right now you have a curved piston top and a flat squish band. Because of that you get a little tight spot right in the middle.
Is there a benefit to going even tighter...maybe but it would have to be pretty big to justify all the work and risk.
[QUOTE=CharlieN;2696671]The mid 0.030s were what I grew up learning on bikes, cars everything. Once I learned to not read books and to read what the engine told me I found quite a bit of difference in a build. If the Gurus say 0.030 then I respect that. If that is a general number thrown out there I will build tighter.
In the engines I build tight there are no deposits in the squish area, granted these have been 4 strokes which to me are more critical due to the unloaded stroke where a 2 stroke is loaded every revolution.[/QU
Wouldn't there be more expansion with a 2 stroke fireing every revolution over a 4 stroke? Gary:confused:
I have used .040 with 1 degree toward the plug and never had a problem.