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jimmer2880
03-13-2007, 08:21 AM
I am in need for a compression tester. After having to guess 1 too many times, I am finally going to break down & purchase one. My immediate need, is for an old 88 Honda 200sx quad. However, I'd also like it to work on autos/inboards as well.

Knowing that I will only use it maybe once per year, are their any thoughts as to which ones to buy, or stay away from? I need to order one within the next day or 2.

trickskier
03-13-2007, 09:59 AM
I don't know how much you want to spend. I do know that Snap-On tools are some of the best. Check out this link.

http://www.snapondiag.com/snapon-gauges.asp

Try this Sears link as well.


http://www.sears.com/sr/javasr/search.do?BV_UseBVCookie=Yes&vertical=TOOL&keyword=compression+tester&gobutton.x=13&gobutton.y=11

JimN
03-13-2007, 10:04 AM
jimmer- I bought mine at either Sears or Auto Zone, since they sell some Craftsman tools. It has a valve to bleed off the stored pressure (like a mechanical hold function) and is the same kind we used at training. IIRC, it was about $39. Harbor Freight has a cylinder leak-down tester on sale now for $29.95, too. Leak-down needs to be tested on older motors with high hours when there are performance issues but the compression is good and nothing else can be pointed to as the cause.

puck_11
03-13-2007, 01:40 PM
Anyone care to explain how to test the compression using one of those testers?!?! :)

JKTX21
03-13-2007, 01:57 PM
1. Make sure your battery is charged.

2. Disconnect the lead wire from the distributor

3. Remove one spark plug, and install the compression meter in place of.

4. Crank the motor and let it turn over a few times.

5. Record the compression from the meter and release the pressure.

6. Re-install the spark plug and repeat on the others.

Note: If compression registers low, squirt some oil in the cylinder and re-test. This will give you an idea if the compression is low because of the piston rings or the valves.

puck_11
03-13-2007, 02:02 PM
Awesome, thanks for the reply!

jimmer2880
03-13-2007, 02:20 PM
Thanks everyone. I'll pick one up on my way home tonight.

I stopped by the local harbor freight store at lunch (only 2 minutes from the office). They didn't have the leak down tester. They did have a nice (and several crummy) compression testers though. They looked just like the Actrons.

JKTX21
03-13-2007, 03:02 PM
I can't remember what compression tester I have, but I bought it from Harbor Freight for less than $15, and it has fittings for different plug sizes.

wesgardner
03-13-2007, 04:36 PM
Slight mod - I've always heard (and done) a comp test with all plugs removed....

JKTX21
03-13-2007, 05:07 PM
I don't see how it could help or hurt? Aside from keeping up with all of those plugs and wires! :)

JimN
03-13-2007, 06:32 PM
JKT- you want the plugs out so fuel can't be drawn into the cylinders. On an injected motor, the injector or fuel pump fuse should be pulled or in the case of a GM, the main distributor harness should be unplugged. That way, the ECM gets no RPM input and will never trigger the fuel pump or injectors.

Compression test should be done at normal operating temperature, too. A pair of mechanic's gloves makes this a lot more tolerable.

For keeping the plug wires straight, I use a Sharpie to number the boot on both ends- that way, I can remove them along with the cap, separately or as a set without needing to refer to the intake or a manual for re-installation. I also mark the dist cap at least with the #1 cylinder position.

jimmer2880
03-14-2007, 06:51 AM
Thanks to all for your suggestions. I picked one up & fired off a test. 130 PSI. Then, went on to play with the kids. Later last night, I remembered that it needed to be done with the engine worm (I did it bone cold). The book said that the compression should be 180-190 at normal operating temp. So - I think that I have found my problem. Going to go back & warm it up first, but I bet the 130 isn't going to move another 50psi. I'm thinking my intake valve may be out of adjustment, & I'm losing compression back into my intake.

JimN
03-14-2007, 09:04 AM
If you had intake valve problems, you'd hear it popping or hissing through the throttle body. If you remove the spark plugs and turn the crank manually (use a wrench on the crank pulley bolt to turn it in the normal direction) and keep your ear close to the throttle body, you should hear no hissing. If you do hear this, it could be a valve that went out of adjustment (very unlikely) or a worn/burned valve. The chance of all of the intake valves being off by the same amount is slight. Also, testing one cylinder won't tell you much. Warm it up, test all of them and post the results.

From the compression numbers you said the manual indicates, you have the LT-1, right? Why do you need to check the compression- did it overheat?

Chief
03-14-2007, 09:23 AM
http://cgi.ebay.com/ebaymotors/MASTERCRAFT-Ski-Boat-Service-Diagnostic-Manual-1997_W0QQcmdZViewItemQQcategoryZ63686QQitemZ190091 039707QQrdZ1

Here's a link for a LT1 service manual on ebay. Correct Link

JimN
03-14-2007, 10:00 AM
That manual is at $51 and that's more than the price dealers were charging for it.

JKTX21
03-14-2007, 11:33 AM
Thanks to all for your suggestions. I picked one up & fired off a test. 130 PSI. Then, went on to play with the kids. Later last night, I remembered that it needed to be done with the engine worm (I did it bone cold). The book said that the compression should be 180-190 at normal operating temp. So - I think that I have found my problem. Going to go back & warm it up first, but I bet the 130 isn't going to move another 50psi. I'm thinking my intake valve may be out of adjustment, & I'm losing compression back into my intake.

180-190 sounds kind of high. The last time I checked the compression on my motor, before I had it tuned, the good cylinders read 135-150 with one reading about 115. My boat still runs like a champ, but it will prob. need a valve job one day. Just a point of reference for you, I have a '96 with 350 EFI.

JimN
03-14-2007, 11:57 AM
The LT-1 has a higher compression ratio but 180-190 is still within the normal window for that motor. 130 would be low if it was at normal operating temperature. As long as the compression is relatively consistent throughout the cylinders (+/- 10%), it should be fine. Really low compression on one cylinder should show up as a plug with black deposits from unburned fuel.

jimmer- I'd still like to know why you think compression is a problem.

JKTX21
03-14-2007, 12:08 PM
Here's pictures of spark plugs with about 10 hours on them BEFORE I had my boat tuned. As you can see some of the electrodes are nearly gone. Runs much better now :)

http://i16.photobucket.com/albums/b19/JKTX21/StarboardLtoR.jpg

http://i16.photobucket.com/albums/b19/JKTX21/PortRtoL.jpg

jimmer2880
03-14-2007, 12:28 PM
First off - thanks again for all the info.

This isn't for my boat, rather a single cylinder ATV (200cc - overhead valves). When I take the air filter off & turn it over I think I hear some air rapidly escaping through the carb. So - that's what is telling me that maybe the intake is still open for a short time while the cylinder is on it's compression stroke.

As far as the 180-190 psi - I agree, thought that was hight also, which is why when I did it's compresison test, when I got 130, I was happy & didn't look any further. Now that I read the manual (RTFM), I see it's not good. However, since I didn't do the test as specified in the manual, it is probably falsely low (should have warmed up the motor first).

anyway - thanks again everyone. There is some great info on here.

JimN
03-14-2007, 01:16 PM
JKT- if the boat they came from is the one in your profile- 1996 with 350 EFI, there's no way they have ten hours on them or came from the factory on that motor. Ten hours of running time in what, three years? Motorcraft on a Chevy motor? NOPE! Also, the rust on the one second from the left shows that it sat for quite a while. The electrode may have just fallen out- I have seen it before and the two outer ones are from either bad gas or really bad setup. I have never seen plugs look that bad after ten hours. EVER.

JimN
03-14-2007, 01:19 PM
Is that quad 2 stroke or 4? If it's 2 stroke, it sounds like it may have sat for a long time, or at least long enough for rust to form on the leaves.

The 130 cold should be OK- if you really want to know, do it warmed up with no plugs, as we said before.

jimmer2880
03-14-2007, 07:58 PM
Is that quad 2 stroke or 4? If it's 2 stroke, it sounds like it may have sat for a long time, or at least long enough for rust to form on the leaves.

The 130 cold should be OK- if you really want to know, do it warmed up with no plugs, as we said before.

It's a 4 stroker. It had been a "camp" quad for most of it's life. Meaning, it was ran for a good bit, probably once every 2 months year round. Hopefully, they didn't rust.

When I get a chance again (probably this weekend), I'll warm it up first & try it again.

thanks again.

JimN
03-14-2007, 08:02 PM
I meant reeds, not leaves.

Sitting for a couple of months at a crack is a good way to waste a motor, especially in a humid climate and even in summer. If it's going to sit, I would spray some fogging oil into it. The reeds are spring steel and will rust in a NY heartbeat if the get the chance.

jimmer2880
03-15-2007, 09:17 AM
I meant reeds, not leaves.

Sitting for a couple of months at a crack is a good way to waste a motor, especially in a humid climate and even in summer. If it's going to sit, I would spray some fogging oil into it. The reeds are spring steel and will rust in a NY heartbeat if the get the chance.

Thanks for the info. When it was a camp quad, it was my parents. I bought it from them 2 years ago & it's been used quite regularly ever since.