Thursday Night Compression Testing
After a lot of discussion about testing for spark and fuel and about why/how the distributor cap got melted on the engine, I decided that the next thing to do was actually not to test for spark and fuel, but to test the compression. Minimum compression per cylinder should be in the 140 psi range and max is around 173. So I ran up to the AutoZone and borrowed a compression tester. More after the jump:
A quick shout out to AutoZone is deserved here. They have a great tool-borrowing program, and they’re open from like 8 am to 10 pm. The tool program works like this. You go and tell them what tool you need to borrow. They get one out of their stock (the compression tester I got was brand new, still in plastic wrap) and charge you the full purchase price. You can keep it for as long as you like. When you return it (in good but used working order), they refund you the full purchase price. How sweet is that? I don’t need to own a compression tester, but it’s nice to have one at this point and not have a time limit on when I need to return it.
I went out into the shop and set up the space heater, as it was getting down into the range of legitimate cold: mid-30’s down to upper 20’s. Even for a guy who grew up in the winter-having states, near-freezing temps qualify as legitimately cold. Thank you Mr. Heater for making the garage liveable even during cold spans!
Given the work that Dave and I did on Blue on Sunday and Tuesday, it was a piece of cake to remove the spark plug cover and remove the plugs. I forgot to take photos, but the plugs were still mostly clean, although they did have a thin coating of oil on them. This isn’t too surprising, since we put a little lube in the cylinders before turning them and given that the top of this engine was bathed in oil by the last owner.
I couldn’t figure out where is the fuse for the fuel pump (there are three fuse boxes on this car but I didn’t see any marked “fuel pump,” even though I know that there’s gotta be one somewhere. I’ve gotta get my hands on what is commonly known as the “BGB,” which is short for Big Green Book, which means the Factory Repair Manual for MR2’s.
But I did pull the line from the igniton coil to the cap so that we didn’t have any mysterious electrical things going on. Then I installed the compression tester on cylinder one, re-connected the battery, cranked the starter, turned the engine over and… nothing. The needle on the tester didn’t even move.
Moved it over to cylinder two. Rinse, wash, repeat: same story.
So am I doing something wrong here? When I turn the ignition, the starter works and all the belts turn, which causes me to think that the crankshaft should be turning and thus the pistons going up and down. Or, alternatively, making some really wicked noises if they were stuck and the crankshaft broken. Right?
Maybe it turns out that the statement “needs engine work” on the Craigslist ad for these cars was the understatement of the year.
On the distributor front, Matt talked to his mechanic in NCarolina, who indicated that if the seal on the shaft failed, hot oil could get into the distributor and cause a small but contained fire inside the distributor that would cause all the melting there. So it looks like we’ll need to pull the distributor from the Red parts MR2 and drop that into Blue. Of course, the distributor is a total pain to get at in these cars, not on the top of the engine like in every other car I’ve ever worked on.
Advice is, of course, always welcomed.
Silly suggestion: does the tester need batteries?
When you crank the starter, does it sound fairly normal? Is it possible that the valves are open/closed at the wrong part of the cycle? I can’t envision how that would be the case, but what do I know? Obviously the spark timing could be bad, but to have a valve open during the compression stroke? Unless they’re just stuck open…but if they’re all messed up or camshafts are broken then again you’d think it would make a terrible noise of some sort.
Unfortunately, the tester doesn’t use batteries. That would have been a nice solution.
It’s a definite possibility that the timing is off. I’m planning to look at that before I test again.
Fortunately, this is a non-intereference engine, so even if the valves were wide-open when the piston is at top dead center (a/k/a TDC), they wouldn’t hit each other. That’s not the case in more exotic engines; if your timing chain/belt breaks in a lot of motors, it means that the piston head will get scuffed and your valve train will be totally jacked.
I’m hoping to get more work done tonight. And I need to find my battery charger and maybe a remote starter button…
I plan on trying to get over there tomorrow. One way to check to see if the valvetrain is working properly is take off the cap and see if the rotor is turning. If not you have a broken belt. You can remove the timing belt cover on the top and leave it off. Suppose to keep the belt cooler. You can see if the belt is ok. There should be timing marks on the cams and one on th crank. You can find TDC markings on these. Pull the valve cover to make sure you are on the right cylce (intake).I also read somewhere you can hack up the lower one and it will keep oil and crud from building up. You have to leave part of the cover b/c it has the timing marks on it. As a bonus you get a little bit if a whine and it sounds like a gear drive or roots blower
@Grayson
I am so glad that we added you to the team.
I like the idea of adding a Roots blower sound. That will go well with the La Cucaracha horns that I’m planning to add on the roof. Maybe we can also add loudspeakers and a tape deck so that it sounds like we’re running a Ferrari V-12 as we drive down the track.
Along those same lines, Captain Slow had a good idea on Monday night’s Top Gear Cop Car Challenge. If we add a horn that plays “Turkey in the Straw,” we can trick other drivers into thinking that there’s an ice cream truck, and then they’ll stop for ice cream and we can drive right by.