newly rebuilt engine - poor compression figures

[suba]

At a recent mapping session on a new engine my car was having issues with knock over 6,800 rpm - 13b single turbo fd3.

As a result of this the engine was then compression tested with the following results:

front - 7.1 8.0 7.4
rear - 6.2 6.5 6.5

Obviously these are way off what they should be, and there is a big discrepancy between the two rotors, which would indicate the issues when mapping.

The engine has now been pulled out as a result.

further info:

1.  Stock mazda parts used - all new seals, springs etc. with PTS 2mm apex seals
2.  Pre-mix run at 500ml per 50litres of V-power
3.  Engine had done 990 miles before mapping after second oil change
4.  Rotors and housings were used, but fully inspected before building up the motor
5.  Engine was also streetported

Does anyone have any ideas as to possible causes?  :confused:

[yehreally]

who built/tuned the engine and what did they have to say about the figures?

[suba]

it\'s being investigated at the moment, and I hope to get it all sorted without too much fuss, so I wont be posting up names - I just wanted comments as to suspected causes.

[Mir]

At a recent mapping session on a new engine my car was having issues with knock over 6,800 rpm - 13b single turbo fd3.

As a result of this the engine was then compression tested with the following results:

front - 7.1 8.0 7.4
rear - 6.2 6.5 6.5

Obviously these are way off what they should be, and there is a big discrepancy between the two rotors, which would indicate the issues when mapping.

The engine has now been pulled out as a result.

further info:

1.  Stock mazda parts used - all new seals, springs etc. with PTS 2mm apex seals
2.  Pre-mix run at 500ml per 50litres of V-power
3.  Engine had done 990 miles before mapping after second oil change
4.  Rotors and housings were used, but fully inspected before building up the motor
5.  Engine was also streetported

Does anyone have any ideas as to possible causes?  :confused:

hi I personally don\'t think premixing or streetporting is to do with low compression, I had a similar situation a while ago, the best advise would be, firstly do u have oil catch tank? If so, did u notice increase flow of oil in it, if u ever notice increase of oil in catch tank, often it\'s ur side seals, who r not either sealing good or the side seals are not cut to the right side, hence less compression and more loss of oil.. How was the starting of the car after rebuild- a first crank start or prolong cranking to start?? Wat seals were changed?? Did u change the oil rings and springs??u said used housings- how was the wear level on them?? Did the engine properly broken in?? Loads of factors but check those I mentioned, side seals if not cut to the right size to the corner seals does cause low compression on new rebuild..

Hope the info helps..

[suba]

Very helpful - thanks.

All the seals and springs were brand new - nothing was re-used apart from a rotor and housing which were good on inspection.

catch tank was not yet connected when the car was mapped - it was on the to do list.

i was not present when the car was first turned over, so can\'t answer that bit.

990 miles breaking in would cover it I would have thought?

[PGiljevic]

PTS apex seals are your problem, they are rubbish.

Put in stock with properly cut new side seals and you will not have the variations in compression like you had nor will you have degraded compression after running the engine for any length of time either.

I have an engine builder friend who went through the same thing with those exact same seals, he never ever will use them again nor recommend them to anyone.

I get many calls each week of people with exact same problem running that garbage in engines, the only solution is to throw them in the bin where they belong! Even if you ring PTS and complain about it they will tell you directly their crap seals are NOT intended to be used in any type of road car application.

I have physically seen them fall out of a rotor slot!!!! due to excessive wear :Hammer with only 10,000miles (less of use). They are rubbish mate.

If you are going to use metal apex seals the only ones to use are Mazda OEM. > http://www.riceracing.com.au/apex-seals.htm

[PGiljevic]

Further to add.

When an engine is built properly on first cranking it WILL have less than a couple of percent deviation between chambers and front to rear, if it does not either your apex seals have been made in a back yard (read any of the ones not made by Mazda) OR your builder has used sub standard parts (outside even Mazda\'s weak specs) OR he has been very sloppy in cutting side seal clearances.

After 1000km running these small chamber differences balance out typically to within 2psi or less of each other, if it does not then its the paragraph above.

In the rotary engine compression thread on here I talk allot about porting and its influence on the actual figures you get and other factors to take into account, but so far as variations this is a big no no when looking front to rear or between chambers on any given rotor.

Good luck with it :Thumbs-up Hope you get it fixed properly.

[suba]

Wow - that\'s the first bad report that I have heard about the PTS seals.  They are not cheap either, and I have been led to believe that they are the best on the market.

All the parts used apart from the Apex seals should have been stock mazda parts - I bought and supplied all the bits, though I have not seen them go in the engine myself.

Why would the PTS seals be responsible? Is it not more likely that the side seals would be the issue?

What would you expect the compression figures to read, and how much variance between chambers and rotors would you deem to be acceptable?

[PGiljevic]

Wow - that\'s the first bad report that I have heard about the PTS seals.  They are not cheap either, and I have been led to believe that they are the best on the market.

All the parts used apart from the Apex seals should have been stock mazda parts - I bought and supplied all the bits, though I have not seen them go in the engine myself.

Why would the PTS seals be responsible? Is it not more likely that the side seals would be the issue?

What would you expect the compression figures to read, and how much variance between chambers and rotors would you deem to be acceptable?

No one of any credibility in Australia or the world for that matter uses PTS end of story. The only application where they are tolerable is when they are totally drowned in oil and run with methanol, anything else and they are rubbish. Way too soft, totally wrong material selection, no hardness to them (so no long term durability) vast variances in normalization so as soon as it goes into an engine they all bend like a banana to whatever shape and this is why you get gross chamber differences. They wear out so fast that its a common excuse by the manufacturer and builders who use them to state you need to do X amount of "run in".

This is not required on any properly made and specified apex seal like stock Mazda or a ceramic apex seal, only on rubbish soft seals will you see such an occurance.

You have to be totally useless to cut a side seal so badly to get the compression variations you saw on your engine, this can\'t really be done this badly but I suppose there is always some who excel at mediocrity ? The Apex seal and lack of conformity are the biggest causes to low compression in the rotary engine.

On a precision build it generally takes around 1000km for the side seal to fully bed into the corner seal and also for the corner seal to bed into its rotor holes also, after this occurs you will get basically even chamber readings.

For raod cars if you are using metal apex seals, Mazda items are the only proven ones to be using, they will take any power level you can make and will last the longest, will work on petrol, and wont need to have as much oil as your whipper snipper to last any decent length of time. :2Confused

[Turblown]

PTS apex seals are your problem, they are rubbish.

Put in stock with properly cut new side seals and you will not have the variations in compression like you had nor will you have degraded compression after running the engine for any length of time either.

I have an engine builder friend who went through the same thing with those exact same seals, he never ever will use them again nor recommend them to anyone.

I get many calls each week of people with exact same problem running that garbage in engines, the only solution is to throw them in the bin where they belong! Even if you ring PTS and complain about it they will tell you directly their crap seals are NOT intended to be used in any type of road car application.

I have physically seen them fall out of a rotor slot!!!! due to excessive wear :Hammer with only 10,000miles (less of use). They are rubbish mate.

If you are going to use metal apex seals the only ones to use are Mazda OEM. > http://www.riceracing.com.au/apex-seals.htm

According to your link it shows OEM seals warping with use-age.That contradicts what you just said....?

I have seen seals warp and the engine shows really poor compression. It could very well be the culprit. I have never used PTS seals however.

[PGiljevic]

According to your link it shows OEM seals warping with use-age.That contradicts what you just said....?

I have seen seals warp and the engine shows really poor compression. It could very well be the culprit. I have never used PTS seals however.

OEM is the longest lasting of all the Fe products, its the hardest thus it is most resistant to chamfering... there is no contradiction, they last many times longer than the pure banana backyard types that have no hardening process done to them and are made from totally non compatible materials for Mazda rotor housings.

Chamfer wear and warping are and can be two different things. OEM\'s will "warp" when not provided enough lubrication or in lubrication failure (no chamfering wear visible)... the banana backyard apex seals made around the world just do this much much sooner, as I have seen over the years of wasting my time trialing them.

:WaveBye

[mx1311]

i can personally tell you the side seals were clearenced accoringly, to what all non race motors are done to
knock at certain rpms on the dyno cant be down to the engine build but some sort of electrical issue, not enough fuel or at worst a bad tune!

in regards to compression, the general rule of thumb is the larger a port, usually the lower the compression will read on a test.

c

[HaywardRotary]

i can personally tell you the side seals were clearenced accoringly, to what all non race motors are done to
knock at certain rpms on the dyno cant be down to the engine build but some sort of electrical issue, not enough fuel or at worst a bad tune!

in regards to compression, the general rule of thumb is the larger a port, usually the lower the compression will read on a test.

c

Sorry buts that\'s not true about compression. Even bridgeports and Peripheral Ports still give good compression figures as do major extend ports also. Having 6 bar is really poor you must admit!!!???

It is true that high knock can come from other issues including an old knock sensor that is more sensitive to knock, or ancillaries such as the power steering pump.

What is interesting is that the engine should have the same porting  front and rear and clearly compression is capable of being 8 bar as there is one reading that is that high, but having so much disparity either denotes a poor engine build or a problem has occured after the build during run in or tuning.

Does your engine builder warranty his engines? If so what kind of warranty?

Regards
Carl

[mx1311]

should have gone to hayward suba

[BlitzBoy]

I dont thinks its the pts seals for the poor compression, I ran 3 years of hard driving on PTS seals on the street and drag strip with plenty of power.

But the original problem of high knock is due to a ignition or fuelling problem surely ?

My theory if there is a problem with fuelling and a problem with one the injectors is not delivering the correct volume this would lead to one rotor running lean causing excessive heat and not enough premix enteriing the housing causing execessive wear over the running in period.

Just checking AFR with a wideband can not detect if one rotor is lean as you would have one rotor running rich which would even out the afr reading.

To the Original poster where the injectors flow tested before the engine was refitted?

I always flow my and clean my injectors before a new engine build is put in better to be safe then sorry