checking compression on an engine without its transmission?

well I've never worked on a rotary but I've always bolted on the starter and it turns the flywheel and vuala compression happens so can someone tell me



why it cant be done on the 13b-rew I have an engine I wanted to go see for my shell .. but the owner is selling it for quite a bit because he says it has 120 compression but he never tried it.. because it has no tranny or harness


which brings me to another question . is it difficult to buy a harness and plug it all in ? and well I can find a tranny ..

 

You could come up with a cheap transmission (any condition) as long as the starter could be mounted, then wire up the battery with a relay on the starter solenoid (as I wouldn't recommend hooking it up directly to the starter).

 

I'll wait for the gurus opinion, but thinking that to check dynamic compression you'll need a transmission and starter. If the engine is out, maybe you could use a big impact at the flywheel nut or front hub.
If in the car, you could turn it by hand but I don't think that would tell you much. I think turning it that slowly compression would leak down some past the seals no matter how tight the engine.

 

Like you said its a lost cause I dont havea trans to mate to it .. and for a shady compression untested engine he's asking for tomuch . anyways

 

How much is he asking? Who rebuilt it? Get all paperwork, there are a lot of things to ask.

 

Its b best to walk away from it. You could find something better were on the forum and off of someone a little more reliable.

-ap

 

FYI, You can not do that to turn the engine. It will not work. That is a good way to break the bolt or strip the nut.



John

 

^How so?

 

^ Depending on what size impact you use. I used a 3/4" impact gun to tighten my flywheel nut. I did not need to use ant type of tool to "lock" the engine from spinning. I know it is supposed to be torqued, I choose not to care. I know it is tight enough.

If you keep trying to turn the engine using the impact gun, the impact gun will keep hammering, it does not apply the force long enough to turn the engine (hence the hammering). Think about this, you jack the front wheel up in the air of your FD. You forget to loosen the lugs before you did that. If you use an impact gun (assuming you have crappy or stock lug nuts) the wheel does not turn. You do not have to hold the brake to use an impact gun even if the wheel is up in the air able to free spin. And I am sure we can agree, the front wheel is a lot easier to spin than an engine making any compression.

Hope that crappy explanation makes sense.


John

 

OK now that I think about it. An impact wouldn't work. I've turned an engine from both those nuts, but your right, it's always slowly and with a big breaker-bar. I have a small brain and just thinking out loud anyway. Gotta stop that.

 

^ No problem with thinking out loud.


Edit: Maybe OP can find a bad transmission... Like one with a hole in the case. And just cut off the bellhousing, then just bolt that up to the engine to check compression. If the transmission is not local it could be shipped a lot easier than an entire transmission.


John

 

You don't need the whole transmission, just the bell housing to mount a starter.

Jack

 

^ +1

 

I have no transmission at all as the car was purchased as a shell .. w/o out I can buy one on its own but then that limits my engine choices since alot of long blocks come with transmissions , he was asking for 1700 for an unrebuilt , stock jdm engine . with unknown miles . no harness , or ECU , or trans

 

i think i suggested you once to stay away from those low miles jdm engines, 90% of the time those engines have being sitting on storage without getting prepared for long term storage.

best thing to do is buy one from a reputable seller here in the forum, or build one.

 

yeah you did . but I like to keep my options open .

 

I'm not sure how that's an option. $1700 for an unknown miles, unknown condition engine is absurd, even with a transmission thrown in. You can get a clean rebuilt short block for not much more than that from a number of reputable vendors.

I still will never understand why anyone would want to put an unknown condition engine in a car. That's a lot of effort to put the engine in and have it go *puff* *squeak* *squeak*

 

Because I need a long block .

 

It's still probably worth half that. Did you have a chance to turn it over by hand and at least see if you get 6 chugs out of it?

 

everything were telling you is for your own good, search the forumn and you will find what happens when you buy a jdm engine.

do you think having to change the engine 3 times is worth it?