piston top clearing cyl top

JW381
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JW381
Edited Date/Time 10/5/2014 9:51pm
I posted about this in race shop but I kinda need some input ASAP. Installing my new Gorr cylinder and the studs aren't even fully torqued yet and I noticed this. Is that part if the mod when Gorr mills the base ?

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slipdog
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slipdog 10/4/2014 3:30pm
10/4/2014 3:30pm
Yes, check the squish with the head on if you're worried. You have head gasket thickness as well as the squish band recess.
JW381
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JW381 10/4/2014 3:32pm
10/4/2014 3:32pm
Okay thanks slipdog, and paw paw for the reply in Race shop.

Next question, how do I do a squish test? Lol
blusmbl
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blusmbl 10/4/2014 3:32pm
10/4/2014 3:32pm
I personally would look at the head side and measure the gasket thickness before worrying about it. Most 2 strokes have no quench area to speak of so they will have plenty of piston to head clearance even if the top of the piston is protruding above the cylinder.

It wouldn't hurt to call or email Eric Gorr.

The Shop

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xnationalwrench 10/4/2014 3:35pm
10/4/2014 3:35pm
Old school way is to assemble with some clay on the top of the piston bolt the head down and manually bring the piston to TDC the remove the head and check the thickness of the clay.
JW381
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JW381 10/4/2014 3:36pm
10/4/2014 3:36pm
blusmbl wrote:
I personally would look at the head side and measure the gasket thickness before worrying about it. Most 2 strokes have no quench area to speak...
I personally would look at the head side and measure the gasket thickness before worrying about it. Most 2 strokes have no quench area to speak of so they will have plenty of piston to head clearance even if the top of the piston is protruding above the cylinder.

It wouldn't hurt to call or email Eric Gorr.
Yeah I'm just trying to hit Albany MX tomorrow and I don't think I'll be able to get ahold of Gorr. There is a pretty good amount of squish recess in the head, and the gasket. So you think it'll be okay, just in your opinion?
Paw Paw 271
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Paw Paw 271 10/4/2014 3:41pm
10/4/2014 3:41pm
I would not run it until you are 100% sure it's correct as it could cause a catastrophic failure!

Paw Paw
blusmbl
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blusmbl 10/4/2014 3:43pm
10/4/2014 3:43pm
Yeah, I'm not going to answer if it's okay because I don't want to give bad advice and have your engine blow up because of it. I will say if you did the squish test and the clearance is greater than .100" I would personally be okay running it, but I would definitely check it first. Use solder, clay, something. I am sure there is enough clearance in the middle but you have to check the edges of the piston top where the clearance is smallest.
JW381
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JW381 10/4/2014 3:45pm
10/4/2014 3:45pm
Okay thanks everyone.
rcannon
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rcannon 10/4/2014 4:11pm
10/4/2014 4:11pm
I'd check it, but my yz 250 was similar....I think you are ok.
JW381
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JW381 10/4/2014 4:20pm
10/4/2014 4:20pm
rcannon wrote:
I'd check it, but my yz 250 was similar....I think you are ok.
Thanks man, gonna go get some solder now.

I know I'm being dense here but what exactly am I measuring before and after?
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YZ125H1 10/4/2014 4:50pm
10/4/2014 4:50pm Edited Date/Time 10/4/2014 4:59pm
rcannon wrote:
I'd check it, but my yz 250 was similar....I think you are ok.
JW381 wrote:
Thanks man, gonna go get some solder now.

I know I'm being dense here but what exactly am I measuring before and after?
Did he cut the head also? As previously said the end measurements of solder are the most important.

JW381
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JW381 10/4/2014 5:07pm
10/4/2014 5:07pm
rcannon wrote:
I'd check it, but my yz 250 was similar....I think you are ok.
JW381 wrote:
Thanks man, gonna go get some solder now.

I know I'm being dense here but what exactly am I measuring before and after?
YZ125H1 wrote:
Did he cut the head also? As previously said the end measurements of solder are the most important. [img]http://www.ozebook.com/compendium/t500_files/morgan/Image2.jpg[/img]
Did he cut the head also? As previously said the end measurements of solder are the most important.

You know I'm not sure. He didn't mark it on the invoice, but he didn't mark milling the base, either, yet it's obvious he did. The invoice wasn't exactly clear..
JW381
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JW381 10/4/2014 5:44pm
10/4/2014 5:44pm
Did the test correct to the best of my knowledge, this is. 093" and it collapsed it about 25-30%

Jakes Dad
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Jakes Dad 10/4/2014 5:45pm
10/4/2014 5:45pm
How a guy can take your cylinder and head, and start grinding and machining. Not knowing where the piston sits in the hole or at what point the ex port opens is beyond me.
JW381
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JW381 10/4/2014 5:48pm
10/4/2014 5:48pm
Jakes Dad wrote:
How a guy can take your cylinder and head, and start grinding and machining. Not knowing where the piston sits in the hole or at what...
How a guy can take your cylinder and head, and start grinding and machining. Not knowing where the piston sits in the hole or at what point the ex port opens is beyond me.
I didn't send a squish measurement, it didn't specify that I had to on the order form. I gotta take a little responsibility, but at the same time, I know what you mean. seems like he would have to have that info, and if I didn't send it, then he shoulda sent it back and asked for a measurement, right? I dunno.
slipdog
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slipdog 10/4/2014 5:49pm
10/4/2014 5:49pm
Jakes Dad wrote:
How a guy can take your cylinder and head, and start grinding and machining. Not knowing where the piston sits in the hole or at what...
How a guy can take your cylinder and head, and start grinding and machining. Not knowing where the piston sits in the hole or at what point the ex port opens is beyond me.
???

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StartedTooLate 10/4/2014 6:11pm
10/4/2014 6:11pm
You use base gaskets to get the port heights right. You machine the head to get the squish right. Basic 2 stroke motor building. Gorr should have given you the specs on the base gasket stack, and the port heights. Get that right, and the squish should be right.
JW381
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JW381 10/4/2014 6:12pm
10/4/2014 6:12pm
So if I'm not mistaken, that looks like enough clearance to me.

I had to kinda reassemble one of the linkage needle bearings, which I just did, so now it's time to bolt everything else down, I think I'm good to go.. fingers crossed.
HazemG
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HazemG 10/4/2014 6:28pm
10/4/2014 6:28pm
Hoping it all works out! Let us know how the bike feels tomorrow! Cool
goinrcn44h
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goinrcn44h 10/4/2014 6:37pm
10/4/2014 6:37pm
.093 seems very thick to me...
I ran some highly modified methanol fueled cr250 engines in micro sprints and I've ran as tight as .038 in certain situations .. I wouldn't go that tight obviously but Gore should tell you what to use with pump gas vs race gas etc..
hillbilly
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hillbilly 10/4/2014 6:45pm
10/4/2014 6:45pm
If the head wasn't machined to receive the piston it wont work.

Before Gorr the piston was flush with the top of the cylinder?

project racer 10/4/2014 6:59pm
10/4/2014 6:59pm Edited Date/Time 10/4/2014 7:01pm
JW381 wrote:
Did the test correct to the best of my knowledge, this is. 093" and it collapsed it about 25-30%[img]https://p.vitalmx.com/photos/forums/2014/10/04/66861/s1200_20141004_174224.jpg[/img]
Did the test correct to the best of my knowledge, this is. 093" and it collapsed it about 25-30%

A cheap set of digital calipers and you would be able to measure the thickness of the compressed solder. With your percentage calculations, .093 solder compressed by 30 %, that would be roughly .065.

A dime is roughly .045 - .047 thick. If the thickness of your compressed solder is at least as thick as a dime, that is about the cheapest, easiest way to measure where you are at. Hopefully you got the solder near the edge of the bore / piston, when the engine was rolled over, and not in the center of the head.
JW381
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JW381 10/4/2014 7:28pm
10/4/2014 7:28pm
Just can't fuckin win, now my rear shock is frozen up. I was re-greasing the linkage bearings, and I've checked each one individually, it's the shock or swingarm bearings. Not sure why. I did have the linkage off for a few days (took it apart, then got busy with the work week), did that cause it to freeze up. It's binding for sure, but it feels like it's internal.

Man, fuck dirtbikes.
jeffro503
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jeffro503 10/4/2014 7:32pm
10/4/2014 7:32pm
JW.....hope to see you at Albany tomorrow if you get that thing going tonight! It's my first ride back in 4 months on my new ( used 06' RM 250 ) ! If you see a RC replica RM 250 down there....track me down!
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jeffro503 10/4/2014 7:34pm
10/4/2014 7:34pm
JW381 wrote:
Just can't fuckin win, now my rear shock is frozen up. I was re-greasing the linkage bearings, and I've checked each one individually, it's the shock...
Just can't fuckin win, now my rear shock is frozen up. I was re-greasing the linkage bearings, and I've checked each one individually, it's the shock or swingarm bearings. Not sure why. I did have the linkage off for a few days (took it apart, then got busy with the work week), did that cause it to freeze up. It's binding for sure, but it feels like it's internal.

Man, fuck dirtbikes.
A shock shouldn't freeze like that. Are you sure maybe the seals didn't dry up a bit and it just got a little sticky? Put some weight on that damn thing and break it loose!
JW381
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JW381 10/4/2014 7:37pm
10/4/2014 7:37pm
jeffro503 wrote:
JW.....hope to see you at Albany tomorrow if you get that thing going tonight! It's my first ride back in 4 months on my new (...
JW.....hope to see you at Albany tomorrow if you get that thing going tonight! It's my first ride back in 4 months on my new ( used 06' RM 250 ) ! If you see a RC replica RM 250 down there....track me down!
Dude that's why I'm so frustrated, I was stoked to meet up with you! I'm still trying. I'll throw the subframe on and see if I can't break it loose..
Suns_PSD
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Suns_PSD 10/4/2014 7:58pm
10/4/2014 7:58pm
Use a straight edge and calipers to measure how far above the torqued down cylinder the piston really is. Then measure the head's squish area right at the very edge. The head should be a minimum of .038" deeper than the piston protrudes. That's straight race gas territory. .045-.055" is pump gas range (it really is the overall compression ratio but these are good rules). Anything over .058" is not really a 'tuned' engine.

The way the cylinder had been dropped so much is going to move the powerband notably lower.

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