Ah right. ok.

My last engine was the only one i had built.

All the rotating assembly parts have come from different engines with all B weight rotors. This is a mix of three engines all Bs even the auto block i got the c weight from. I thought it must have been out of balance cos of damage at the top of the rotors which on closer inspection was ruled out.

Now i dont think my assy was out of balance. im putting it down to a poor batch of fuel or the front rotor having a better flowing port at high rpm. I have checked the ports and they measure identical and are of equal smoothness and shape. I didnt get my ports gas flowed.

cheers

 

i have not had my injectors flow tested. it may be an idea. cheers. They are low mileage and about 2 years old

 

Third time request for pictures.

How much chamfer are you using on the exhaust port? How much rise are you getting on the plug boss area. In other words... what is breaking your apex seals?

Barry

 

Barry.

Chamfer on the exhaust ports on the exit its stock but i opened up the sides and the bottom a little, not much chamfer on the opening

 

photos as requested

 

Sleeve,

Thanks for the pictures.

I guess that the other two apex seals that were not destroyed were still damaged heavily from the shrapnel
but examine their faces for scars at the area where they scrape the side of the exhaust port.

Run your finger across the edges of the port. Anything for the apex seal to catch on? I use cheap diamond files from Harbor Freight to chamfer the hard chrome liner in this area. Remember that the hot exhaust gases actually cause some expansion of these sharp edges.

Notice the lifting of the seal in the area of the sparkplugs. This is where cold plugs help.

I like your idea of using the stock exhaust port closing shape. It helps fight reversion flow to the intake.

Barry

 

Barry,

Im taking the block i built on wednesday apart on saturday and going over the exhaust ports. I have increased thier size and need to check they are smooth and chamfered correctly. I read about closing shape and left ot stock to reduce overlap as the intakes go quite low.

When you say lifting of the seals do you mean the "creep" the brown mark. can you explain how colder plugs manage to help against this.

10.5 in the L or 11.5s. the housing was used so probably had teh same marks pre rebuild.

 

good advice on checking the seals (if i hadnt thrown them away)

 

an out of balance engine won't just toss an apex seal, it will give vibrations and eat bearings.

failures can be mysterious, unless you have a log of the drive while it happened to point out inconsistencies, even then it can be difficult to pinpoint because injectors being out of balance with one another will not always show on an AFR log as an issue.

 

Fair point.

im going to try to log my track use next friday and see what it throws up. hopefully not another tip.

 

Sleeve,

The lift is from heat expansion in the spark plug area. Full explanation in this thread.

https://www.rx7club.com/showthread.p...t=barry+bordes

We need to port the water jacket in area 5.
Barry