Hi All,

I rebuilt my engine last year, however, the car was very hard to start and was running really badly. A compression test showed 6.2, 6.3, 3.8 on the front rotor.

I have stripped the engine back down now. The front rotor was showing low compression on 1 reading, down about 3.8 bar.

The front face of the rotor I could not see any problems. On the rear face I have one Apex of the rotor where the side seals do not spring back up as much as I would like to see. Even without the corner seal in place, they stick down in the seal groove.

Also, on the below picture you can see evidence of carbon blowby beside the corner seal.

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Could this be the area causing the low reading?

I was pretty pedantic about side seal clearances, but I have now realised that I did not check the clearance between the side seal and the groove itself.

The Factory service manual calls for 0.028 - 0.078.

With the above seal near the apex I couldn't get an 0.03 feeler between the seal and the groove.

It's like the grooves have shrunk - This rotor was in the old engine which overheated.

Is it replacement rotor time or is there a way to remedy this?

 

It's hard to say, the big thing is the side seals need to be able to spring up and down in their grooves nicely.

When cleaning I take the end of an old side seal and run it through the slot back and forth. If it hangs up in a spot, work it back and forth on that spot until it can move freely.

Binding should be fixable. It can also be caused by a side seal that's bent out of shape slightly.

Are the springs underneath new?

You should be able to press on pretty much any part of the length of the side seal and have it pop back up.

The only issue I've ever seen with side seal grooves was a motor that sat after a water seal fail for a long time causing the seals to rust in place. Besides that I've always been able to clean up and work with the grooves so the seals move properly.

Dale

 

Make sure when you check your side seal groove clearance you remove your corner seal and drag the feeler gauge all the way through the side seal slot into the corner seal pocket.

It is somewhat common for the side seal grooves to become pinched tighter right there at the side seal pocket because the whole tip of the rotor from the apex seal groove to the side seal groove can get crushed in a bit if you handle a rotor rough.

A stuck/broken side seal is what will cause a low compression reading on one rotor face.

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Opposite of the above, check your apex seal clearance with the corner seals in place.

That brand aftermarket corner seal has had the apex seal slot cut off center before and may need to be clearanced.

 

From that picture, it looks like a 2 mm apex seal in a 3 mm corner seal.

 

Thanks, this is exactly what I am seeing here - I cannot slide the 0.03 feeler past and into the corner seal hole when the corner seal is out. It is like there is a pinch point at this corner of the rotor.

 

Definately 2mm apex seals and 2mm solid corner seals all bought from Atkins last year.

 

I used a 400sand paper IIRC to grind the groove little by little until each side seal spring back up nicely. It was Almost as Long as cutting the side seal to proper length.

 

Get rid of those solid corner seals and get some oem ones. My compression increased by almost 20psi on all faces after I replaced my Atkins solid corner seals with two piece oem corner seals.

 

Detonation or mishandling of the rotor can cause the side seal slots to pinch. From the mark at the 10 o'clock position on the rotor, it looks like one or both of these occurred. Hit that ridge with a file to take to down. Like stated above, hit it with some sandpaper in order to try to get the clearance back into spec. I also recommend getting rid of those corner seals. Stock will make more compression. If you want solid corner seals go with the version with no recess from Atkins. Also hard to tell from the picture, but your side seal to corner seal clearances look loose. I recommend .002 for most applications. The Mazda spec is far to broad.

 

Why do the stock corner seals make more compression than the Atkins solid seals?

And if this is the case then why to Atkins even bother to sell them?

 

2 piece design seals better. This is why Mazda went with multi piece apex seals as well. The recess in those seals also puts more pressure on the irons as there is less surface area to distribute the load. I believe the intension was less friction but I have noticed these cause more wear. If you want solid corner seals go with the style with no recess.

 

They say there are no stupid questions so here goes:
1) Is the .002 gap corner to side clearance on both ends of the side seal? If so, that would mean that a properly fitted side seal would have .004 of "play" right?
2) what do you use to measure that gap? I have standard feeler gauges. Is there a .002 probe or something available?

 

1)The side seal to corner seal gap is the total gap measured from one side with the side seal butted up against the opposite corner seal.

2)Standard flat feeler gauge is the tool used to measure the side seal clearnce (both the sides and side seal to corner seal gaps).

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A couple tips.

Make sure the side seal you are measuring is down in its slot with about the same amount of side seal sticking up all along the slot and same with the corner seal.

Don't manipulate the side seal when you are measuring. Even with allowable slot wear there is enough play along the side seal length to bow the side seal slightly which will exaggerate the gap.

Just gently drag the long side of the feeler gauge between the corner seal and the side seal until it slips between them.
If it slides freely out, the gap is larger than the feeler gauge you are using.
If the feeler gauge catches, the gap is smaller than the feeler gauge you are using.
If the feeler gauge drags out with a constant and light friction that is the size of your side seal gap!

Next, make sure the corner seal and side seals pop back out without binding when pushed down both individually and together and then each one again with the other seal all the way depressed.

Mark the outer surface of the side seals with permanent marker. If you don't grind the end perfectly perpendicular the side seal can bind when placed with the long corner down (even with a good gap) and not bind with the long corner up with a good gap.

Once you are done with all side seals clearances, put all the corner seals and side seals in the rotor again and do the above binding test with all seals in place.
This is done since doing one side seal at a time can push the corner seals outward if there is any play in the corner seals.

 

.002 total clearance, meaning push the side seal all the way against one corner seal and measure the other side. I use SnapOn feeler gauges but you can use anything quality.
.004 is too loose for most applications and will result in more blowby.

For the corner seal make sure it springs up and down freely and protrudes a minimum of .5mm above the rotor. If the side seal is pinched, it is very possible the adjacent corner seal slot will be affected.

 

Hey all, thanks for the replies and advice. I appreciate the input.

Here's a wee video I made yesterday showing me pressing the seal in and it not popping back up.

https://www.youtube.com/watch?v=NmXS...ature=youtu.be


I've decided I'll just replace this rotor.