Compression question (New, never asked before)
Thread Starter
Open up! Search Warrant!
Joined: May 2002
Posts: 3,838
Likes: 3
From: Kicking down doors in a neighborhood near you
Compression question (New, never asked before)
You guys who have rebuilt engines before know how they can be hard to start after a rebuild and they can show lower compression numbers until they are broken in. I was wondering; what did Mazda do to the engines when the RX-7s were new? I wouldn't think they would sell a car that is a bitch to start cause its engine is new. What did Mazda do to solve this problem?
Senior Member
Joined: Oct 2002
Posts: 333
Likes: 0
From: Driver's Seat
Re: Compression question (New, never asked before)
Originally posted by Project84
You guys who have rebuilt engines before know how they can be hard to start after a rebuild and they can show lower compression numbers until they are broken in. I was wondering; what did Mazda do to the engines when the RX-7s were new? I wouldn't think they would sell a car that is a bitch to start cause its engine is new. What did Mazda do to solve this problem?
You guys who have rebuilt engines before know how they can be hard to start after a rebuild and they can show lower compression numbers until they are broken in. I was wondering; what did Mazda do to the engines when the RX-7s were new? I wouldn't think they would sell a car that is a bitch to start cause its engine is new. What did Mazda do to solve this problem?
When I got my new engine installed in my old NA with a streetport it was still easy to start. Fired up everytime with minimal cranking all the time. Was not a huge port job done on it though. But new does not equal tough to start. Not if its built properly.
a new engine or even a rebuilt engine with new rotor housings and seals should be very easy to start and have good compression. the main reason people have trouble with compression numbers on rebuilds is because they have old housings with new seals (takes longer for the seals to seat in the worn housings) or they port them.
Joined: Oct 2003
Posts: 11,576
Likes: 27
From: Morristown, TN (east of Knoxville)
For a change, bitchmill is right about something.
When they were new, every sealing surface in the engine was perfectly shiny, flat, and slick. They didnt make perfect compression, but they did well enough not to have any running issues. Just like a piston engine freshly started up before breakin...good compression, but it will still improve slightly with proper breakin.
Same thing here.
Most rebuilds use one ore more used housings. This isn't the mark of a necessarily inferior engine, but it does mean things won't seal nearly as well to begin with, and thus combusiton won't be as even or complete as it would otherwise be. So they start hard and run rough.
Porting only adds to this issue.
When they were new, every sealing surface in the engine was perfectly shiny, flat, and slick. They didnt make perfect compression, but they did well enough not to have any running issues. Just like a piston engine freshly started up before breakin...good compression, but it will still improve slightly with proper breakin.
Same thing here.
Most rebuilds use one ore more used housings. This isn't the mark of a necessarily inferior engine, but it does mean things won't seal nearly as well to begin with, and thus combusiton won't be as even or complete as it would otherwise be. So they start hard and run rough.
Porting only adds to this issue.
Trending Topics
Lives on the Forum
Joined: Feb 2004
Posts: 5,721
Likes: 3
From: Coldspring TX
I had heard so many horror stories on this site about rebuilds being so hard to start/ idle that I was prepared for the worst when I just completed mine, but...new rotor housings, that's the ticket...started up exactly 4 seconds after the key was first turned, and settled at a 900 rpm idle, little lumpy at first, but after 200 miles she's purring at 750 (and I'm just ITCHING to romp on her 
)
)
Thread
Thread Starter
Forum
Replies
Last Post
trickster
2nd Generation Specific (1986-1992)
25
Jul 1, 2023 04:40 PM