mirabile

Hey guys,
A friend of mine just recently took apart his 20B because his compression numbers were low but even across all rotors.
We found all the housing to be in perfect condition, but also something none of us had ever seen; a baked on sludge build up above the exhaust port, and the same build up across on the other side. Here are some low res pictures because a camera phone is all we had. Any ideas on what the issue could be? A timing issue perhaps?

mirabile

This build up was easily cleaned up with carb cleaner and the housing looks pristine with it cleaned off. Could it be that it is pre-igniting?

allrotor93

iTrader: (126)

the black is normal. when its like that sometimes it skips across the port without sealing very well causing the lower but even numbers. have you measured your housings to see if they are in spec? if so, just clean it off and freshen everything up. i am sure it is fuel related in some way but completely normal.

Juiceh

iTrader: (4)

Who works for Comcast, and can they hook me up with free cable?

t-von

iTrader: (8)

Has the engine been opened before? If so I would check the side seal to corner seal clearence. Most people don't understand how important that clearence is when it comes to making really good compression. I've personally seen a 30psi swing in compression difference on my own engine in a past experiment.

Also whomever Mazda uses to do the remans here in the states, do a half assed job. Recently I had a Mazda reman apart to replace the coolant seals due to over heating. The engine had brand new rotor housings and less than 10k on it. Anyways I checked the side seal to corner seal clearence and was shocked to find they were all over .006. The client didn't want me to replace them but I explained to them "the engine will run fine, but you will have hard starting do to slightly lower compression". The engine is back in the car running fine but is experiencing those exact symptoms I described before.

crispeed

What apex seals are you using?
Check and make sure they are not warped.

patman

iTrader: (3)

looks to me like your friend drives too slow. Generally if you open it up fairly often it will burn that carbon slidge off there. Is there gooey stuff in the apex seal grooves too?

RETed

I've seen it before...
That's what happens when you run synthetic engine oil with the stock oil injection.


-Ted

mirabile

Some more background -
He does not drive slow, at all - He was at 174 in 4th gear last week before all of this.
He pre-mixes with marvels mystery oil, which is something I was wondering about.... One water bottle per full tank.

RE-Red- can you elaborate?

I really appreciate all this help.

This engine had new housings and the engine had 2500 miles on it before this happened.

RETed

Me?

One of the local guys was running Amsoil 20W50, and it had deposits just like that.
The engine had be torn down at under 10k miles due to other problems, but the deposits were starting to look like that.
It was heavy right around the spark plugs.

It sure looks like something isn't burning "clean" and leaving those deposits.
I dunno how much a "water bottle" is, but it might be the MMO.
Why didn't the owner use a proper pre-mix?


-Ted

turbotommy

iTrader: (3)

guys, thank you for all you input so far. It is my car and the car ran great. Every seal in the motor was replaced. I bought the motor used and had every seal replaced ( apex, corner, side, springs, oil seals, water, etc...) also, 3 new 13b rotor housings. the motor has approx 2500miles on it. It doesnt smoke at all, sounds great, and ran great, however, the car started to stall at idle. I changed plugs, checked for vaccum leak, put a good wideband sensor in there to make sure the computer wasnt dishing more fuel bc the sensor was bad. all those things didnt help. so for the hell of it i decided to check compression. Like i said the car ran great. i drive the hell out of it. take it to the track. do 170mph pulls. its a nice little street car. it starts right up everytime. etc. well. i got about 60 across the board on all three chambers and they are all even pulses. So, i just pulled the motor and took it apart and there are big blotches of black build up (almost size of a softball in circumference above the exhaust ports.) I dont think that is Normal. Ive seen a thousand motors and have never seen that. ya a little black here around the spark plugs etcc. but not like that. Im going to have to get better pics. Its like baked on there. i use marvel mistery oil because thats what i always used to premix. Ive been using it for about 5 years now and never had a problem like that. Every thing (Seals, housings, etc) are in spec. etc. all that stuff looks good. real good. I dont know. I just wanted to see if you guys had any ideas. BTW: all the parts are new mazda parts. I hope to figure this out because id hate to be taking the motor out every month n a half to clean build up off my housings.lol I dont think i could put something in there to clean it either because i had to apply a decent amout of pressure to get it off because its baked on there. ( not like id want to).. The buildup was fairly thick also. Thanks again guys and i appreciate everything so far.....even the driving slow comment. I WISH that was the problem. haha

t-von

iTrader: (8)

What did you clearence your side seal to corner seal clearence too? That carbon build up isn't going to cause compression readings to dip that low on new housings w/new seals. I broke my 13rew engine down a couple months ago. It had 108k on it with the same carbon on the housings. I never used synthetic oil but it still had compression readings in the mid 90's before I blew the engine due to over boost.

RETed

Did you change fuel?
The MMO might be reacting with a change in fuel?


-Ted