methanolhemi
New member
A calipers should be fine to measure the cylinder height as they most likely took of more than .005''.
squish question
- Thread starter maxco
- Start date
You are getting good advice here as you need to get down to the base gaskets and check/measure all the components to sort this out.
Decking a cylinder is as you thought removing material either from the top or bottom of a cylinder....I have only seen them with material removed from top. This is typically done to decrease squish and increase compression. This is uncommon on a two stroke because usually the heads are modified or replaced to accomplish squish/comp ratios.
I run Peak heads on a couple of my sleds and I will caution you to ensure all the cylinders are the same height as the Peak heads clamp the head inserts like a sandwich and then bolt down to the cylinders like a solid one piece head. If the cylinders are not all even the head must bend to try to seal to the surfaces and they will leak.
There are a lot of O rings used to seal up the Peak assembly so I would suggest you get a spare set from Peak as they are very hard to match/find elsewhere.
Some info:
My 99 700SX
-stock installed cylinder head volume was 23.25cc = 11.0:1 comp ratio
-squish stock was .074"
-Peak heads I am using have 22cc installed head volume = 11.6:1 comp ratio
-squish = .064"
Hope this helps:
Bob
Decking a cylinder is as you thought removing material either from the top or bottom of a cylinder....I have only seen them with material removed from top. This is typically done to decrease squish and increase compression. This is uncommon on a two stroke because usually the heads are modified or replaced to accomplish squish/comp ratios.
I run Peak heads on a couple of my sleds and I will caution you to ensure all the cylinders are the same height as the Peak heads clamp the head inserts like a sandwich and then bolt down to the cylinders like a solid one piece head. If the cylinders are not all even the head must bend to try to seal to the surfaces and they will leak.
There are a lot of O rings used to seal up the Peak assembly so I would suggest you get a spare set from Peak as they are very hard to match/find elsewhere.
Some info:
My 99 700SX
-stock installed cylinder head volume was 23.25cc = 11.0:1 comp ratio
-squish stock was .074"
-Peak heads I am using have 22cc installed head volume = 11.6:1 comp ratio
-squish = .064"
Hope this helps:
Bob
Devilin AblueDress!
New member
Please dont be offended, I only mention this per your statement of not being a mechanic. Clean up the area around the base of jugs and side of jugs prior to pulling them. If theres any little peice of crud on them you dont want it falling into cases as your pulling it apart. Just getting the jugs back on track will give you a lil better throttle response. Along with the peak head should have more giddy up when your done!
none taken
I really do appreciate all the advice, and with little prior knowledge, please do not make assumptions about what I might know. Think "explaining it to a child". I Haven't heard yet, is stacking the gaskets a problem? It looks like I might be looking at that to resolve this problem. Even up the tops, and alow proper squish.Thoughts
I really do appreciate all the advice, and with little prior knowledge, please do not make assumptions about what I might know. Think "explaining it to a child". I Haven't heard yet, is stacking the gaskets a problem? It looks like I might be looking at that to resolve this problem. Even up the tops, and alow proper squish.Thoughts
Bob Thanks for your input
I bought a new set of head gaskets, and a new set of o-rings from MPI for the Peak head. I guessed it needed to be perfectly flat, which is why the squash qued me off to the descrepancy. I am currently pulling it all apart again. I will see if I can download some pictures later. I have the head off currently, and am looking at pulling the jugs. Fingers crossed. The good news is that I do not see any damage to the piston tops. I was concerned that with that low of clearance the spark plugs danced on top of the pistons, but all seems well. I had this together last night and had the engine running briefly. I was worried that the clearance .024 had damaged things. I will get measurements off the jugs and post tonight if all goes well. That will determine what needs to be done I guess. I am wodering if shimming will work? Add one more layer to the middle, and call it good. Thoughts on this anyone? I will of course check the difference in heights and shim accordingly. Then make sure I am getting the proper squash. It looks like I will have to have a similar amount of layers 4-5.
I bought a new set of head gaskets, and a new set of o-rings from MPI for the Peak head. I guessed it needed to be perfectly flat, which is why the squash qued me off to the descrepancy. I am currently pulling it all apart again. I will see if I can download some pictures later. I have the head off currently, and am looking at pulling the jugs. Fingers crossed. The good news is that I do not see any damage to the piston tops. I was concerned that with that low of clearance the spark plugs danced on top of the pistons, but all seems well. I had this together last night and had the engine running briefly. I was worried that the clearance .024 had damaged things. I will get measurements off the jugs and post tonight if all goes well. That will determine what needs to be done I guess. I am wodering if shimming will work? Add one more layer to the middle, and call it good. Thoughts on this anyone? I will of course check the difference in heights and shim accordingly. Then make sure I am getting the proper squash. It looks like I will have to have a similar amount of layers 4-5.
If you could somehow adjust base gasket thickness between the three cylinders to ensure they all were the same height at the cylinder head gasket surface that would work but IMO that will be hard to do. Once you have the cylinders off and everything measured it will probably become very clear what needs to be done to correct the issues.
Who knows...maybe someone has already added base gasket thickness to try to correct a mismatch in porting specs between the cylinders...trying to match up a stock cylinder with ported ones...
Pictures and measurements would be very helpfull.
Who knows...maybe someone has already added base gasket thickness to try to correct a mismatch in porting specs between the cylinders...trying to match up a stock cylinder with ported ones...
Pictures and measurements would be very helpfull.
more info
So I have the Jugs off. There are 2 layers of metal gasket the same single pieces covering the bottom of all the jugs. I measured the jugs #1 is Exhaust can side. 88.54 mm from bottom to top. #2 is 88.28mm. #3 is 88.48mm. Anyone know what a stock jug should run? Remember this is a mountain max. So any way the middle cylinder is .2 short of matching. They all have some variation apparently (?) They look to be ported. I know there are different levels? of porting. What little I know looks like it was done on the bottom of the cylinder wall(?) It does not look like they actual ports in the cylider wall have not been touched. They do not look like they have been machined. Doesn't look like tooling marks.
So I have the Jugs off. There are 2 layers of metal gasket the same single pieces covering the bottom of all the jugs. I measured the jugs #1 is Exhaust can side. 88.54 mm from bottom to top. #2 is 88.28mm. #3 is 88.48mm. Anyone know what a stock jug should run? Remember this is a mountain max. So any way the middle cylinder is .2 short of matching. They all have some variation apparently (?) They look to be ported. I know there are different levels? of porting. What little I know looks like it was done on the bottom of the cylinder wall(?) It does not look like they actual ports in the cylider wall have not been touched. They do not look like they have been machined. Doesn't look like tooling marks.
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I just dug out the original untouched OEM cylinders from my 1999 700SX[I installed ported ones on it 12+ years ago]. With my digital verneer all three of them measure 89.5mm from bottom to top gasket surfaces.
If they are ported, the top of the exhaust port should measure less then 31.5mm[stock]...typically when these are ported the exhaust will be brought to 30-30.5mm from top of cylinder...among other things.
From the pictures, it is obvious that the cylinders have had some work done to them as the sleeves have been modified to unrestrict the intake that is caused by the reed cages on these red heads....maybe thats all the porting work they did?
If the ports have not been raised you could take the cylinders to a machine shop and get their height evened out then raise them with layers of base gasket to get the squish you desire...kind of a poor man's porting job.
LOL!
Used to be good for beating tech inspections as well!
From the pictures, it is obvious that the cylinders have had some work done to them as the sleeves have been modified to unrestrict the intake that is caused by the reed cages on these red heads....maybe thats all the porting work they did?
If the ports have not been raised you could take the cylinders to a machine shop and get their height evened out then raise them with layers of base gasket to get the squish you desire...kind of a poor man's porting job.
LOL!
Used to be good for beating tech inspections as well!
Sorry...no cylinders for sale at this time...never know when I may need them! I have enough spare engine parts and in some cases spare engines to rebuild or reengine every bike,sled,4 wheeler,or boat I own! LOL! Its a real sickness!
I have the calipers that are a little to big to fit easily into the cylider. I cannot get them down to gauge the distance. I used a steel rule, and I couldn't tell. 1 inch 5/32 is my guess. Not seemingly helpful. I tried to measure up from the bottom, but the cylinder flange is in the way.
I dont know about those head bolts. they look corroded in place. If I were to machine this, obviously they need to come out. Can any competent machine shop do this or does it need to be specialized? And back to the question in my mind how bad is gasket stacking. In my mind it seems like a problem from the standpoint of leaking, but what else could happen? Just a question. Thanks
On second thought...measuring the top of your exhaust port to top of the cylinder[on inside wall] will be inaccurate on cylinders that have had their tops machined!
The top of the exhaust port from bottom of cylinder sleeve on stock cylinders should measure 87mm approx...
The top of the exhaust port from bottom of cylinder sleeve on stock cylinders should measure 87mm approx...
ok now I am a little confused. The bottom of the skirts look to be factory, but they are not the same measurment from one to another. from the gasket surface on the bottom to the bottom of the skirt they are not the same distance. ???????
methanolhemi
New member
Looking at the 2nd pic the side exhaust ports (2 small ones) look to be enlarged. That is typical in a port job. I would get a stock yamaha base gasket
and cut all three jugs to the same height (deck them to match the lowest one).
Then have the peak domes recut to get you to .055'' squish minimum and you should be good to go. Probably run stock 3 layer head gasket?
and cut all three jugs to the same height (deck them to match the lowest one).
Then have the peak domes recut to get you to .055'' squish minimum and you should be good to go. Probably run stock 3 layer head gasket?
Devilin AblueDress!
New member
I would check prices @ machine shop to have the taller 2 cut match shortest. Then figure out how much extra you need in base gaskets to give yourself proper squish. I wouldnt be doing the 5 layer head gasket trick any longer. If your making the differance up any where do it @ the base gasket. The pressure base gaskets hold back are nothing compared to the pressure your head gaskets hold back. After you have a total of what that will cost, price replacement jugs and go from there. Cant help but wonder why? What was the last guy thinking? Maybe they got hot and warped? Maybe the guys first (hopefully last) whack at porting? Cant imagine his goal was to deck all them a different height?
staggs65
Moderator
maxco said:
sounds like they were decked on the bottom. I do believe when I was discussing my engine build with Mrviper he said he decks the bottoms. Now I could be wrong on that as alot of info has gone through my head on it but thats what I'm remembering.