205 lbs. compression?

dan filipi · Dec 22, 2010

Ok I've got a real head scratcher here.

I put the 1200 cam in the right side, adjusted valves and I have 205 lbs. compression :headscratch:

I've double checked timing and valve adjustments, no problem there.
Both cams are "UP" on the pulley which is where they were before pulling it apart.
Exhaust and intake are opening as they should, rockers are square on the valve stem and cam.

I thought maybe I adjusted the exhaust on a lift point resulting in too much play of the rocker but hand cranking it while feeling play is good.

What am I missing here?? :headscratch:

mcgovern61 · Dec 22, 2010

Is the compression tester clean and at zero before you start? Is it 205 on all cylinders?

dan filipi · Dec 22, 2010

It's 155 on the left side both cylinders, both right are 205.
Tester is at zero.

mcgovern61 · Dec 22, 2010

Same springs?? Same valves?? Same heads?? Just different cams?

dan filipi · Dec 22, 2010

Only cam has changed.
Same heads, valves, springs, rocker holder etc.

mcgovern61 · Dec 22, 2010

Looking at your picture of the 1200 vs 1000, the 1200 has a shorter duration which to me translates to a longer period for the valves to be closed building compression? If that is true, you risk blowing the head gaskets.

dan filipi · Dec 22, 2010

Yeah, that's why I don't want to risk starting it til it's sorted out.

It seems to me the only way compression can build that high is if the exhaust valve isn't opening to let the compression out but the exhaust valves are opening.
Maybe not opening enough?

mcgovern61 · Dec 22, 2010

Ehhhh, it doesn't take much to build compression if you can get a longer period with the valves closed. Thats how a diesel works!

Omega Man · Dec 22, 2010

While looking for a reason for the increase in compression, I found that a cam change can definitely increase your compression.

~O~

dan filipi · Dec 22, 2010

I was told by the seller these cams came off a engine with less the 5k miles.
Just 5k miles is suspicious but I gotta believe they at least came off the same engine since the left is labeled left and the other is labeled right and they are in like condition, showing hardly any signs of wear.

I didn't check the lobe heights against another 1200 cam. Think I should do that?

mcgovern61 · Dec 22, 2010

Dumb question, are both of the heads from the same engine and are they both 1100 heads?

dan filipi · Dec 22, 2010

mcgovern61":2r16xf0w said:
Dumb question, are both of the heads from the same engine and are they both 1100 heads?

Uncertain. They could be 1000 heads, one or the other or even both.
I haven't found a way to identify them yet.

AApple · Dec 22, 2010

Did you ever have the opportunity to check the compression before you changed the cam(s)?
When I first read the post, the first thing I thought of was different combustion chambers for the two heads. But since all you changed was the cams on one head, Gerry might have a point about the duration differences in the two styles of cams. If you have an intake valve that is closing fairly early(comparatively speaking) on the intake stroke, that will definitely up the compression reading.
I'm wondering if the 1200 and 1100 cams might not be indexed differently(advanced/retarded), in relation to TDC, meaning the slot for the keyway may be machined slightly different, to advance/retard the 1200 cams, compared to the 1100.... :headscratch: :read:

mcgovern61 · Dec 22, 2010

Okay.....another dumb question....did you check the compression before changing the cams? Just so there is a comparision. (Aren't I full of dumb questions today?) :mrgreen:

I am under the opinion (for what it is worth) that mixing and matching is going to produce these kind of results.

EDIT: :doh: Joel, ya beat me to the question!

dan filipi · Dec 22, 2010

Right now it has a 1200 cam on both sides.

Before putting the 1200 cam in the right side it read 155, same as what the 1200 cam reads in the left side right now.

I thought maybe could be getting some hydro compression because I DID smell gas but I cranked it with the plugs out to clear them in case, didn't see any spray of anything and compression is still 205.

Indexing of the cams is a thought but now that I have 1200 cams in both sides they should be the same, no?

jdegase · Dec 23, 2010

AApple":3qpxdihs said:
Did you ever have the opportunity to check the compression before you changed the cam(s)?
When I first read the post, the first thing I thought of was different combustion chambers for the two heads. But since all you changed was the cams on one head, Gerry might have a point about the duration differences in the two styles of cams. If you have an intake valve that is closing fairly early(comparatively speaking) on the intake stroke, that will definitely up the compression reading.
I'm wondering if the 1200 and 1100 cams might not be indexed differently(advanced/retarded), in relation to TDC, meaning the slot for the keyway may be machined slightly different, to advance/retard the 1200 cams, compared to the 1100.... :headscratch: :read:

you would definatly want to use the sprocket(pulley) that matches the cam.. the sprocket keyway and timing marks may be different to index the cams to different motors.
stay with it, you'll figuer it out.
just a thought, but if 185 is "healthy" then 155 is slightly low, and 205 is slightly high.
since one gear is exactly the same except for being flipped over on the 1000 and 1100, maybe the 1200 has specially machined gears(pulleys).
following me??

AApple · Dec 23, 2010

:headscratch:
That IS weird...
Seems like there must be some sort of difference in that cam(obviously). The comp readings were the same on both sides before the swap, and all you did was swap that one cam... :headscratch:
My only idea would be to swap the cams left/right(pita, I know), and see if the issue changes sides with the cam...

scdmarx · Dec 23, 2010

I'd watch for detonation and cranking/starting problems. Other than that, I say put the other one in and go for a test ride! :yahoo:

arty:

jdegase · Dec 23, 2010

a qiuick check in the parts manuals confirms 1000 and 1100 have the same part numbers for cam pulleys, 1200 has a differnt part number.
bet you need to keep the cam pulleys with the cams. 1000 pulleys with the 1000 cams, and 1200 pulleys with the 1200 cams.
we used to sell cam indexing keys... offset cam keys for SB chevy engines. they would make ruff idle cams smoother for automatic trans.. while keeping the lift and duration.

joedrum · Dec 23, 2010

dans something wrong on your end there nothing that different to cause whats going on .....recheck recheck .....i dont know what .....with no fuel pump drive it might be in there backwards or somthing ...meaning the cam im sorry i didnt look at this earlier...i bet thats what it is maybe .....that would have the close time hugely long ..... :mrgreen:

205 lbs. compression?

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