I am tearing down my L-88 spec 427 and am hoping I can tap into the collective knowledge here. I purchased this car over the summer and have not had a lot of chance to drive it. Performance has been relatively good, but the prior owner messed up everything he touched. I was told that the engine was purchased freshly rebuilt from a trusted source. #7 had a funny knock at low RPM (I thought maybe piston slap) and I felt some vibration during acceleration in neutral. I figured it was best to go inside and check the bearings for problems. I also wanted to put in a new cam, but wanted to verify the internals before making assumptions about the 12:1 compression. The engine was reported to have less than 2000 miles since the rebuild. \\

I pulled the lifters the other day and there was minimal wear on most.

Today I pulled a head. The following is a picture of the tops of pistons 1-7. 3 & 5 have a shiney goop on the top. Should I assume that is oil? If that is the case, is the likely culpret bad valve seals?

 

Well you said in your last thread that you had 3946074
aluminum heads, they are an open chamber head with around
118/119cc chambers, the pistons in your engine are closed
chamber ment to work with a 101cc closed chamber heads, so
its safe to say you don't have 12.0 comp. I can't tell for
sure by looking at the domes if they are 12.0 pistons ment for
closed chamber heads or some of the 11.0 versions. Besides the
oversize clean one of the tops on the pistons looks like there is a
piston number on them.

 

Thanks for remembering the details of my other thread.

The pistons are L2239N .030. I found the Flatand site this morning and it says they are closed chamber pistons. It also indicated that these pistons produce a compression ratio of about 10.75:1 with 118CC chambers (which I beleive is provided by the the 074 heads. I am hoping that should open up my cam options. Will there be any inherent problems with running these pistons with the open heads? Should I get a larger head gasket to get it down a little lower?

I will post a different thread on cam selection after I shore up some of the problems I am finding.

 

The cylinder has about a .001 - .0015 ridge. However, I can see slight smudges of rust color on the cylindar wall. It looks like water marks on a glass when they come out of the dishwasher. I am guessing there was a period of long inactivity where light surface rust developed. It is fully glazed over and you cannot feel any surface variation on these marks.

Do you think that I should do a light hone and replace the rings or leave it as is?

Here is a picture:

 

Open chamber heads with the easy to find flat top pistons give almost no comp, and most all open chamber pistons are very big dome for
racing, its hard to come up with an in between piston for open chamber
heads so a lot of people just use a the old style dome closed chamber
pistons to gain some form of comp. your heads show to be 118/119 cc
every cc counts for lowering or raising comp. The shape of the
closed chamber piston is not ideal for the open chamber head but
it won't hurt anything. You need to find out what the dome volume
of the L2239N piston is, how far the pistons are down in the hole
and figure in the the cc volume of the head gaskets you are going to use to get a better picture of how much comp you will end up with.
It would also be nice to know how deep the valve pockets are on
your pistons in case you decide to go with a very high lift cam.
At least find out what the dome volume is and the volume is on
your gaskets your going to use that will give you a rough idea
or guess at what comp you have.

 

I'm have a problem believing the 2000 miles, I don't see any cross
hatch left in the cylinder. you said you thought you had a knocking
noise on the 7 cylinder. pull the bolts out from your idler arm drop
the drag link down pull the pan look at the number one rod bearing
and number seven rod. To be honest If I were
doing it as expensive as block repairs and parts are these days I would
pull the engine down check everything out, you will be out your own labor a few new parts. at least take a look at your bearings.

 

I am in the process of a complete tear down to see the bearings. This is what I was originally concerned with. I thought that I could check out the bearings without cutting the ridges and removing the pistons if I wasn't going to hone the cylinders.

The more I think about this, the more I think that I should really hone the cylinders and install new rings. I probably need to check the piston to cylinder gap in #7 to see of that is why I am hearing noise. Is this good logic?

I will go rent a reamer tonight and pull each of the pistons. Should I be ok with a light pass of a 220 grit hone to break the glaze and then install new rings?

 

I found the following from the Flatlandracing site:

L2239N - 30
Compression @ 116.9 - 10.84
Compression @ 119 - 10.62
Comp. Dist. 1.760
Dome Size .438 dome

This is about all I can find for that piston. Does anyone know the cc displacement of this piston?

 

Are you sure you have a ridge looks more like a little rust above
the ring travel. You need a dial bore gauge.

 

There is definately a slight elevation change at the end of the travel. I can feel it with my finger. I put my smallest feeler gauge (.0015) next to it in order to gauge how big it is. I estimate it is about .001. I can slide the piston to that point and it stops at the ridge. I pushed lightly, but it didn't go past the ridge. Do I need to ream something that slight? I was afraid to push too hard and break the land.

The ridge arae looks more like bronze than rust.

 

You don't have that much wear, you won't hurt the top of the piston.
move the crank pin to the farthest bottom point push the piston up till you hit the little ridge, take the wood end of a claw hammer put
it in the center of the upper rod dead center under the I-beam of
the rod. take another hammer hit it that will push the rings closed
enough to push it past the ridge. the ridge will be gone after you hone
it. As long as your hitting the rod under the center of the I-beam with
wood you will be alright.

 

per my speedpro (aka TRW) cat:
L2239NF30 bbc 4.280", 1.760", .438" dome, +43.1cc DV
L2239NF60 bbc 4.310", 1.760", .427" dome, +42.3cc DV

1/16, 1/16, 3/16 ringpak, press or float
marketed for L88, ZL1, closed chamber heads

-edit-
It is not uncommon for local shops to machined down domes. Verify what YOU have.

 

Ok. I ran them down the bore just a bit harder and they came right out. This is my first time, so I really appreciate the guidance.

I think I found the noise in my #7 hole. The #7 piston pin is tight in certain spots. There is definately something in there that is keeping the connecting rod from freely pivoting. There is also a spot on the side of the piston that I am sure is from rubbing against the cylinder wall. It would make sense that an inability to pivot would push the piston against the cylinder wall.

This is consistant with my observations, as it only made the sound at low RPM and there isn't a lot of wear. I can't see any visible wear on the cylinder wall in the same spot. Is the piston softer than the wall?

In my configuration, the pin appears to be pressed into the rod and the piston rotates about it. There also appears to be bushings pressed into the piston and the rod looks hardened. Are these actually bushings? Should I be able to purchase these and replace them or will I need a new piston? Will I be able to press out the pin without a press or will I need to go to a machine shop?

The rod bearings have only slight wear and it is consistent across each rod. I did one with plastigage and it was .003. I haven't pulled the crank yet.

Now the clyinder walls. There were two pistons that had a lot of scraping near the top. Here is a picture:



I think that there was rust that formed at the top of these cylinders, as there is evidence of surface rust in several bores (now glazed over and can't be felt). I think the engine was started after inactivity and pieces of corroded metal scraped the piston tops and the cylinder walls. I have a couple of scratches in two bores, likely from the rust event. They are about .001 deep. Here is a picture:



Will I be able to just hone this and put new rings back in? It would seem that a scratch of this magnitude should not impact blowby too much. The scratches are in the middle of the piston travel, not at the top. Your thoughts and input are appreciated.

 

The second problem that I found was end play in #1/#2 connecting rods. The end play was about .032 and the spec, accourding to my Hayes manual, was .015 - .025. Is there a way to put a shim of some sort in there? I have read that I need to rebalance the whole lower end if I replace a rod or two. Any suggestions here?

Thanks again for your generous support and guidance. It is really appreciated.

 

Rod side clearance of .032 will cause some noise in thin oil situatuons. No shims available. Your slight knocking may be there. Replace all the rods as a set. Before you do this make sure the wear is not on the crank pin itself. You will need inside mics for this or let your machinist do it. Also the rod big end thickness is to be checked as well. The shiney spots on you pistons could be from water getting into the combustion chambers. Maybe not but get your 074 heads pressure checked before they go back on. They will leak around the seats. Resurface the head and deck the block if money allows this. Those closed chamber domes are made for closed chamber heads. The flame travel is destorted and the power goes down when mismatched. This may also be the reason for shiney piston tops. More consistant carbon (black) should cover the entire piston. Where the top is clean no combustion is taking place. I bet this is the problem instead of water since it is on all piston crowns. The side skirt wear looks very minimal on the piston shown. I have some suggestions for a cam with a high compression setup if you are interested. Remember, more duration on the cam will lower compression at low rpms and sometime you can get away with high compression on pump gas.

I have a 67 L88 torn down for assembly currently in my shop.

 

You need to take your block, crank, rods, pistons, pins to a good machine shop that has the tools to measure with let them look over your parts. Find out what machine shop does a lot of the race engines in your area has a good rep,
don't just shop who has the best price or who is closest to you.

 

also, it may ... repeat may turn out rods are in spec from side to side ... but fillet/radius on crank journal is worn ... resulting in wide rod side clearance. Some good shops have a crank WELDER machine ... if they have a good operator too then they can bring badly worn/damaged journals/radii back into spec. Done right, it's as good or stronger than new crank ... but done wrong it'll snap. Gleason is a good name in crank welders.

 

I measured the rods and journals last night. The #1 rod is about .005 thinner than the others. Also, the #1/#2 journal width is about .005 wider than the others (I only quickly measured the shoulders in 1 or 2 places last night).

The end play was at the low end of spec in some of the other rod pairs. By exchanging the #1 piston/rod with the #3 piston/rod, for example, I could get everything in spec. Will this create a balance problem for me? Can I make the swap if they weigh the same?

Thanks for your assistance here.

 

Sure you can swap rods if they weigh about the same.

Chances are, they'll weigh a little different.

Rods & other engine balance stuff is usually measured in grams. Also, to accurately balance motor you must know individual ends of each rod ... big end grams & little end grams ... shops use a rather delicate jig to measure end weights.

Ideally, rods'll be matched (overall weight) to within a gram or 2 ... but ... in all honesty GM never balanced bobweight that close ... So even if they're several grams different I'd use it in a STREET motor.

FYI ... for a 90 degree motor (sbc & bbc) bobweight is figured by summing these:
2x mass of 1 rod big-end
2x mass of 1 rodset of bearings
1x mass of 1 rod little-end
1x mass of 1 piston
1x mass of 1 ringpak including any support rail
1x mass of 1 wristpin
1x mass of any 1 pistonset of pin locks
about 4 grams of clinging oil (some folks don't do this)

Above just for reference ... other than swapping rods to tighten side clearance ... have a pro manage the balancing. Suggest you take it to a shop sooner than later & have everything inspected & measured w/ pro gaging; you take notes.

 

2000 miles? No way pal.