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Discussion and questions related to the course Practical Engine Building
I am new to engine building and have a 94 Camaro with a LT1 small block chevy. I bought the car fully prepped for the road race series I am targeting and the prior owner had swapped to a 96 LT1 crate motor. I ran the car for the first time this year and had several significant overheating events/blown head gaskets due to the OEM radiator not matching the crate motor. I have the cooling resolved with a new radiator but I am now getting smoke under acceleration and I suspect the rings. I am planning to do a leakdown test to confirm.
My question is: presuming the problem is the rings how will I know if I need to simply "refresh" the engine with new rings and valve guide seals etc. versus a full "rebuild" honing the cylinders but also checking and correcting clearances in the bottom end?
I am new to all of this and was wondering if there was a consensus on when one needs a rebuild vs. refresh.
Many thanks in advance
You disassemble the engine, and examine each of the parts. That tells you the minimum amount needed to refresh the engine. A full rebuild, often you are planning on new parts anyway, so skip inspection of parts you don't intend to re-use.
From what you say, it seems you made a habit of cooking the engine? As such, you may need to do a full re-build, including a rebore, to ensure you have a healthy engine as it's not unusual to have piston and/or bore damage from excessive overheating.
As David said, until you pull the engine down and see what you are actually looking at, you don't know what you need to do. A leak-down, or compression, test will only give a partial indication of the ring seal as it's under compression from the chamber, it can't tell you what the ring seal is like under vacuum or what the oil control rings are like. A boroscope inspection through the spark plug hole, with the pistons at BDC, can give some idea of the bore condition and from that the ring and piston condition - if there's damage or scratches...
With the oiling side and bearings, you're not going to tell without dropping the sump to check them, or doing a full strip down - they may be prestine, but if the builder didn't do a proper clean-out you may be looking at new bearings, or worse.
Because it's been cooked, you're going to be looking at getting the heads skimmed to make sure they're flat as they're aluminium (aluminum to you) and can easily warp which can result in poor sealing. The block should also be skimmed while it's apart, too, as it's aluminium and also can warp slightly when over-heated and/or may have some surface damage from leaking gases, which will also promote loss of gasket seal.
Then, because of the engine's design, the intakes are most likely going to need to be machined to correct the geometry.
A lot is going to depend on budget and time constraints - if you have the time and no hurry, do the strip-down and get the work done as need and budget allows. If you have a decent budget and time pressure, assume you're going to need a full re-build with a next oversize rebore, etc, so consider what you're going to use the engine for as there are some good package deals for improved pistons, bearing, connecting rods, camshaft, etc. Maybe some head and valve seat work?
It's MUCH easier and cheaper to do any internal upgrades now rather than pull it out again later or, worse, do other mod's that over-stress the OEM parts.
So just to repeat what you all are saying to make sure I am understanding:
I should expect to pull the engine no matter what and measure the clearances. If my components are within spec I could Re-use them replacing rings and seals etc. If not I will need to correct the damage and it is difficult to know in advance with certainty
I previously decked the heads but not the block. This block is cast iron and the heads are aluminum.
Presuming the bores are in spec do they still need to be honed to accept new rings even without oversized pistons? I am hoping to turn the engine around for the new season in a few months
thank you all for your help!
While you can remove the heads, drop the sump, and remove the pistons with the block and crank in place, it's a PITA doing so and keeping everything clean.If you pull the transmission, you can even drop the crank and pull the camshaft, etc.
It's much, much easier to pull the engine as is - a good excuse to buy a hoist and engine stand, they can always be used again, or on-sold if not wanted.
If the engine oil was clean, you may certainly find the crank bearings and journals to still be serviceable (I've had bearings re-used twice on engines, but I was very fussy about cleanliness and oiling, and the engines were relatively unstressed), but it's easy to check with the crank out.
If the bores are free of scratches, or scuffing, it will probably be serveable with a light hone - this will normally be required to break the glaze for re-ringing, so expect it to be needed for correct ring seal to be developed. If the pistons are free of scuffs, scratches, etc, they should be re-useable. A reputable engine builder should be able to make the call for you if you're unsure - same on the crank bearings and journals.
Ah, current spec'n had the blocks as alloy, but lots of details change over the years - iron is heavier but much more resistant to warpage or gas erosion from a leaking gasket - an engine shop will check that with a precision straight-edge.
Yes, honing should be considered as required for ring seal.
It's not going to be cheap, but one thing I've learned over the years is that trying to things "on the cheap" will almost always come back to bit me on the bottom and cost a lot more in the long run - if in doubt, spend the money and remove that doubt.
Forgot, "anti-freeze" not only lowers the freezing point, but raises the boiling point significantly at the trade-off of a little worse thermal capacity transferring the heat from the engine to the radiator. This can often give a power advantage.
If not already part of the engine's coolant plumbing, fitting the 'steam port' (IIRC) conversion is cheap insurance to reduce the possible build up of steam pockets in the block/heads that can cause rapid overheating in the area.