Help! Uneven Compression on New Motor

[badvinny]

Is one high, or the other low 25, and you owned this motor before also right?

Watcon must be correct that something is wrong on the mag side. I just don't see how 36cc domes get you 200psi unless the cylinder has been decked or modified. You didn't answer if you ran this motor before the boring, or if you owned it before either.

 

[///M5]

Watcon must be correct that something is wrong on the mag side. I just don't see how 36cc domes get you 200psi unless the cylinder has been decked or modified. You didn't answer if you ran this motor before the boring, or if you owned it before either.

Yeah it's racking my brain too, so when I pull it I will report back. I never ran this cylinder before. Picked it up from a member here as a Blue ported Cyl @ std bore, but it was in need of an overbore.

So you think that the mag is reading low at 175?

 

[badvinny]

I do, because there is virtually no way to make a cylinder run 25 psi high!, that cylinder is most likely not standard height. 35cc domes and 200 psi just sounds too high to me, even if you are at sea level, my 61x with those domes I got 165 at 1650 feet above sea level, so I went 33 for 180-185.
Plus, I don't think you should only have the minimum of. 040 or 1mm squish just by adding a head.
And if you didn't notice, the head picture 5 on the first page shows damage or detonation on one dome only (If it was a newer undamaged dome) most likely the higher comp cylinder, you either need better fuel or less compression or it won't last!

 

[Blue]

If it is one of the cylinders that i ported for a customer it is possible that the top was cut down to true the top of the cylinder due to the sleeves dropping in the oem cylinders. If this is the case the compression could be around 200 psi especially if its rich and has extra oil helping to seal the rings. The problem is not the rear cylinder being to high the issue is the front is to low which is most likely caused by a pinched ring or smeared piston sticking the ring. Pull the cylinder and let us know what u find.

Sent from my SAMSUNG-SM-N920A using Tapatalk

 

[///M5]

I do, because there is virtually no way to make a cylinder run 25 psi high!, that cylinder is most likely not standard height. 35cc domes and 200 psi just sounds too high to me, even if you are at sea level, my 61x with those domes I got 165 at 1650 feet above sea level, so I went 33 for 180-185.
Plus, I don't think you should only have the minimum of. 040 or 1mm squish just by adding a head.
And if you didn't notice, the head picture 5 on the first page shows damage or detonation on one dome only (If it was a newer undamaged dome) most likely the higher comp cylinder, you either need better fuel or less compression or it won't last!

Domes are perfect w/ no signs of deto. It's just some grease crap on them when I took the pic.

 

[///M5]

If it is one of the cylinders that i ported for a customer it is possible that the top was cut down to true the top of the cylinder due to the sleeves dropping in the oem cylinders. If this is the case the compression could be around 200 psi especially if its rich and has extra oil helping to seal the rings. The problem is not the rear cylinder being to high the issue is the front is to low which is most likely caused by a pinched ring or smeared piston sticking the ring. Pull the cylinder and let us know what u find.

Sent from my SAMSUNG-SM-N920A using Tapatalk

I'm going to pull it, and I'll post back up once I have it out.

 

[badvinny]

[QUTE="///M5, post: 1809975, member: 14059"]Domes are perfect w/ no signs of deto. It's just some grease crap on them when I took the pic.[/QUOTE]
There is either detonation or pitting marks on the exhaust side of the lower dome in that pic, zoom it in and look!

 

[///M5]

It's just dust from the bench/rags, and WD playing games with the shadows. The domes are still perfect.

 

[nick matthews13]

Dos you happen to find problem ?

 

[///M5]

Dos you happen to find problem ?

Not yet, I have been riding it a lot and I don't want to down the ski.

 

[Harbor]

Did you try a different gauge yet... ?

 

[///M5]

Did you try a different gauge yet... ?

Yes, it's the same with other gauges

 

[Harbor]

Ok good

 

[///M5]

Well guys, I finally decided to pull the Cyls and guess what... It was a bent ring making the comp (exactly 25psi) lower on the MAG Cyl. You can see from the pic that the ring was getting stuck and staying stationary in the ring-land.

When I pulled the head to inspect, the piston would move side to side like normal, so I did not think this could be the problem. It must only get stuck once it's up to operating temp.

The last time I had it out I thought I felt a partial seizure right after my pissers got hot. Looks like I toasted the piston, but the cylinders still look like they are in good shape. Also, the head has tiny pits from Deto that weren't there the first time I pulled it to inspect.

Now, I'm going to clean the Aluminum off of the bore with acid, and see how bad it is after a quick hone. Then I'm going to install 1 new piston and rings.

Anyone have a 82mm ProX Kit laying around?

 

[Nuklear6]

That close up of the bore shows it is in need of some attention. It appears to be out of round. I'd suggest checking with a bore guage if you have access to one. There are areas the cross hatch is still mint from the last hone and areas that is totally gone. A ball hone will make it all look good after but has no ability to make the hole concentric just the ability to put a new surface finish on it

Chuck Palmucci
CPT Enterprise LLC
609 510 3062

 

[///M5]

I'm definitely going to mic the bore. I think I caught it in time to get away with a hone.

The camera is not showing it, but the only area that I can't see crosshatch is the scuff mark.

 

[john zigler]

I may have a piston kit for you. ( Have many Pro-X) Please call me at the shop 608-743-1305 or email me watcon@watcon.com and remind me to look. If I do not have one, I can get one in a few days. Also have gaskets, etc.

Your mag piston looks leaner than the PTO. I would suggest going through your carbs, do a leak down test, check your jetting, etc. If you have deto you are lean.

 

[///M5]

Thanks John,
I already pulled the carbs to go through them. I was also thinking it was lean due to the higher comp in the Mag Cyl.

 

[badvinny]

Thanks John,
I already pulled the carbs to go through them. I was also thinking it was lean due to the higher comp in the Mag Cyl.

The Mag side was the lower compression at 175, because of the bent ring. Otherwise we would all go bend our rings just like that for the extra psi! Lol

 

[///M5]

The Mag side was the lower compression at 175, because of the bent ring. Otherwise we would all go bend our rings just like that for the extra psi! Lol

Yeah sorry, I put it backwards lol.

Correction, everyone was right. Bent ring side reading lower. Earlier post corrected.