88_Import_Slaye

Well, I borrowed a compression test gauge from a friend. Since I have the summit shorties, getting to all plugs is impossible without removing the headers. I'll be doing that tommorow. However, i did manage to do #4 cylinder (2nd in on pass side of motor).

One the first tick of the gauge, it went to around 90psi, then each stroke after that didnt do much. After 4 ticks of the gauge, it was at 120psi, I cranked it a few more times and the gauge finally ticked its way up to 150psi.

What does this mean? This is my first compression test ever. What should I normally be reading?

Specs:

(Fresh = cleaned, checked, worked, etc)

fresh 305 @ 0.30 over = 310cui
fresh 416 heads with 1.92/1.6 valves
nothing special felpro head gasket, dunno the size
flattop pistons w/2 valve reliefes
214/224 112 lsa hydrolic flat tappet
1.5 roller tip rockers

I think thats all you need to make a judgement, if not let me know.

This is in regaurds to my previous post about my lack of power and how it was suggested that I might have my valves stuck open due to incorrectly setting the lash.

Thanks.

88_Import_Slaye

also, on each crank, should the pressure go up in even incriments? for example, +50psi each gauge tick? or will it always vary? If it varies, will the first stroke always be higher?

Dialed_In

iTrader: (3)

you need to do the same # of "clicks" for every cylinder to maintain accurate results. I usually go 5 revolutions of the motor. What you're looking for is major differences between cylinders. 150 psi doesn't sound awfully bad, but not super either but every motor will be different because of size of cam, intake port volumes and such. Do the rest and let us know what you get.

88_Import_Slaye

well, since I did the valves all the same, if I get the same reading on all cylinders, that doesnt tell me if the valves are being held open. Not worried about bad rings, it's a freshly built motor. New rings/pistons, blah blah blah. Not to say there is no chance of a bad ring, but there are no other signs of bad rings. No blow by on the spark plug, no smoke in exhaust, etc etc.

I'll do the rest tommorow and post the results

Dialed_In

iTrader: (3)

since you did what to the valves?

Just because it's a new motor doesn't mean squat. Rings may have been washed out, not worn in yet, cracked. Block might not have been honed properly. Valves may not be sealing or could be hanging open/bent.

A compression test only tells you how much pressure is being built in the cylinder. If it's leaking pressure or if it's not building pressure, a leakdown test will tell you where it's leaking.

88_Import_Slaye

results:

1: 135
2: 130
3: 135
4: 130
5: 135
6: 130
7: 130
8: 135

what do you think? No one has a leak down gauge for rent around here. Should I attempt to redo the valve lash and try again?

I did a dry test, did not do a wet test

88_Import_Slaye

well, it seems that if i charge my battery, I get higher results. My batterty was at 57% when i did the first round of tests. I charged it up to 72% and did #1 and #3 cylinder and I get 150psi on each.

I'm starting to think it is a timing issue.

mnorton

It's important that the battery is fully charged when you do a compression test. The Throttle Plate must be blocked open, and all of the spark plugs must be removed. Do the same number of cranks each time, I did five. Also it would be a good idea to prevent the injectors from fireing just to prevent any possible cylinder wash. I removed the injector wire plugs and turned the fuel pressure all the way down.

Here are my results which I think are typical. The engine has 145K mi. on it.


Pass. Driver
PSI CYL PSI
167 8 7 162
162 6 5 162
156 4 3 160
166 2 1 165

Firebat

iTrader: (7)

After i'm done turning it over, the pressure seems to slowly drop a little bit. Do i take the reading asap or do i wait until the pressure stops slowly going down?

mnorton

The bleed down is caused by the gauge, the o-ring seal at the spark plug hole, or the piston rings, maybe all three. Take the highest psi reading, and be consistant in your technique for all the cylinders. They should be in a range of ~ +/- 5% from the median psi value.

SSC

As far as cold pressure goes thats about normal. Is there anything other then lack of power? Usuually a stuck valve will cause a very noticeable miss.

88_Import_Slaye

No, just lack of power. When the car is out of gear, it sounds great, very responsive, but when in gear with a load, it's a$$.

Supervisor42

Need more info on the build.
The link on details: ("all about my mods") http://www.programmers-unlimited.com/camaro
will not work.
Curious about the hydraulic flat tappet cam in an "88" block, the induction system and how the '416 heads got 1.92 valves.

88_Import_Slaye

what do you mean? I gave the heads to a friend, he took them to his shop, stripped the heads, hot tanked them, checked the springs and put in new ones where needed, and then he did what ever u do to put in bigger valves. I bought the valves from summit. Trick flow.

The cam is a summit cam sum-1103 http://store.summitracing.com/partde...5&autoview=sku

and it's not an 88 block, it's an 85 block. The link is down cause I am too lazy to buy a dedicated server again.

This is a 100% rebuild. Fresh motor. The short block was torn apart & cleaned, checked and rebuilt by Waynes Engine Rebuilding in so. california. Cost me $600.

88_Import_Slaye

http://24.124.74.223/camaro/

there is the history

Supervisor42

The carb and distributor are new. I suggest verifying the distributor timing curve first. The cranking compression seems fine to me. In neutral, note the timing at idle, 2000 rpm, and 4000 rpm, with the vacuum advance connected.
This will help:
http://www.jegs.com/webapp/wcs/store...tegoryId=22163
Also during assembly of the engine this should have been done:
http://www.cranecams.com/?show=article&id=3
It can be done later with the engine in the car minus headers.
Lastly, verify the carburetor is providing correct mixture to the engine. We can delve into this later.

88_Import_Slaye

I've already assumed that the timing is off after doing compression tests and thinking about everything. I think I make have moved the rubber on the balancer out of position, so I think the timing will be off anyway. However, when we did the timing, the motor was not idling. Since we didnt have a tach on it at that point, I assume it was at least 1500+ rpm. I read that the mechanical advance may have been put in, thus causing us to time the motor less than we wanted which was 15-18 advanced.

I'll be putting everything back on tommorow and retiming it.

Also, I think it is the timing because of my previous flooding problem. Having not enough timing would cause the mixture not to burn right, this flooding the motor, which was what was happening. I had to fix this by changing the lever position on the arm on the carb for the pump. I bet once I correct the timing, I'll have to move it back to where it was or i'll ping.

88_Import_Slaye

Well, I put everything back together and did the timing test. Here is what happened

First, i'm using a craftsman "Advance Inductive Timing Light" which is a timing gun with a dial, you set the dial to what you want in degrees advanced and when you are dead on, the marker will read 0* on the timing tab.

Now, I started the car, let it run for a minute, then idled it down. It was around 500-800 on the tach, but that is with the idle screw all the way out...dunno if thats good or bad, but that is how it is.

When I disconnected the vacuum advance, I got a reading of 20* BTDC. Now here is the funny part, when we set the timing originally, we had the dial on 15*. So what does that mean?

Next, assuming the timing marker is off, I rotated the dizzy counter-clockwise a bit. I shot again and got 30*

I put the vacuum advance back on, revved it a bit. It didnt sound as loud as it normally does. (Open header btw). I took it for a test drive around the parking lot and it felt a bit more responsive and felt like it had a little more power, but I really couldnt tell. I havent driven it since i started this thread.

I do get some popping though on the top end as I let off the gas.

So did I go the right way on the dizzy to advance it?

I have the dizzy setup where the vacuum dohicky is on the pass side of the carb pointing to the #2 cylinder. I'm not sure if I have the wires setup right, but there is no missing on any cylinder, so I guess I have it right. There are no marks on the damn cap so we had to guess.

Supervisor42

Yes.

Every manual has a picture of the top of a distributor and where the wires go.

88_Import_Slaye

We DID use the manual and just happened to get lucky. The image shows wire location, but does NOT show how the dizzy is indexed, unless it's on another page. I believe it was on the accel paperwork that it says that the dizzy should be indexed with the vacuum canister pointing to #2 cylinder. That is how I have it. Is that wrong?

Supervisor42

Supervisor42

EDIT: I don't know what the accell distributor looks like but when you can move it alot without bumping into anything, that's where it needs to be.

88_Import_Slaye

I didnt get a chance to look at the timing at other rpm's. I will do that as soon as i can.

mw66nova

iTrader: (13)

hmmm...30* of initial timing, plus mechanical advance and vacuum advance...that thing is going to ping till the cows come home!

i would suggest backing the timing back down to about 12* initial on that motor.

88_Import_Slaye

the problem is, i dont think the timing is right because of the balancer. I'm going to go buy a new balancer, unless someone can tell me how to correctly index the marker.

SLEEPER 86

find a sparkplug style tdc indicator.
screw it into the # 1 sparkplug hole,BY HAND,rotate the engine clockwise slowly until the piston makes contact with the stop.
make a mark on the balancer(noting the position in degrees on the balancer).then rotate the engine the other way,until contact is made again.make another mark on the balancer.measure the distance between the two,divide that in half,and that is your zero mark.if the mark has moved,you should probably consider a new balancer.
get a timing tape and set it to exatly where your zero is.the balancer needs to be clean for it to stick.
get an adjustable vacuum advance can,install itand set it to it,s 1/2 way setting.get a set of advance weight springs,installthe two silver springs for starters,you can mix n match these.start the motor,let it warm up or drive it for 20-30 minutes.
disconnect your vacuum advance line at the distributor and plug it.
attach the timing light to #1 cyl.
make a note of the initial advance,it shoould be between 8-12*
rev the engine until the timing quits advancing,and make a note of the rpm.if your springs are right,it should be about 2800-3000 rpm.adjust your springs until you are in this range,write down the exact rpm.
set the static advance(turn the distributor) so you have right around 36* at the rpm you just measured.
hook the vacuum advance,and go for a drive!
lug the engine a bit,and listen for pinging.if you get some,back the vacuum advance can off(careful,they adjust backwards!),if you don't,bring in more.once you are on the bare edge turn out the screw about a turn(it's pretty sensitive).
that will get you a good starting point,i wouldn't be suprised if you ended up with 1 silver and 1 blue spring.

Eric B

SLEEPER 86

by the way,a variance of 10# on compression is considered ok.

88_Import_Slaye

here's a dumb question and possibly my incredably dumb problem.

Do the accel dizzy's come with springs already put on or do you have to put the on? Because I did not put on any springs, and I went to the part store to check it out, I did not see any springs already on the dizzy. It comes with a pack of springs and a handy allen wrench though.

Should I smack myself?

fb305svs

just an aside - those compression test numbers for a cold motor with stock compression heads and a 112 lsa cam, sound just about right

SSC

Well I smack myself just for getting up everyday.

They come with the gold (light) springs installed so your fine there.

I'd just use the best vacuum then -2 method for setting your advance until you can get a correct reading. Vac guage to full manifold vacuum then advance timing until it peaks then falls. Bring it back to that point then back it down until it drops two more inches of vac. Then see how the engine runs. If it runs a whole lot better we will know.

88_Import_Slaye

Well, I found the problem. Timing. I bumped it up another 10* and I got sideways on my test drive. BUT, i'm at like 65* according to my balancer. Got a removal tool, gonna check it out and make sure it's right, but the real problem is the vacuum advance. It was way too low. I am going to turn down base timing and up the vacuum advance and see where i get.

Checking my mechanical advance, it semmed to only advance the timing by 10* is that normal?

five7kid

iTrader: (14)

Sounds like you have a 12 o'clock damper and a 2 o'clock timing tab.

88_Import_Slaye

DOH! Probably. I bought the timing tab from advance auto, it "said" it was the right one. any part numbers for the right one?

five7kid

iTrader: (14)

I've never seen a 12 o'clock aftermarket tab (that I recall).

What did you end up doing?

88_Import_Slaye

well, i upped the vacuum advance and i have not yet tested the car. Gonna see what I can do to get it running as good as i can for now.

Are there different balancers for my 305? Do I have a 7" or an 8" because Mr gasket has a tab for each. I got the tab for a 7". I was gonna see if I can move my tab up a bit to see if that will give me a little more accurate readings?

As far as I know, it's the stock balancer that came with the motor. I have not chekced yet, but a new balancer has the timing notch aprox 10* counterclockwise to the crank key. I am going to check mine and see if it's correct or close.

five7kid

iTrader: (14)

Yes, there are different dampers. 6-3/4" (close to 7", I guess) is typical, although some have reported having 8" on a 305 (I believe my '79 Caprice 305 had an 8" damper - but that memory is fading).

Both 12 o'clock and 2 o'clock (approximately) have been used as well. My '86 was at 12 o'clock but the '87 LB9 I picked up was a 2 o'clock mark (that 10 degrees off of the keyway that you mentioned).

A piston stop (TDC finder) is not a bad tool investment. I think I paid $12 for one at the local non-discount speed shop. My new damper & timing tab for the 396 turned out to be 2 degrees off.