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Author Topic:   life of cylinder walls on a fresh block?
Dirt Freak

Total posts: 334
posted September 15, 2005 02:49 PM  
If you start with a good .10 or .20 over block, and have everything balanced and assembled professionally, how many races / laps do you expect to be able to run before the cylinder walls need to be bored out? 2 seasons, 3 maybe?? You are left with a good rotating assembly at .10 or .20 over, so you prep another block for these components. Then you take the used up block and bore it out, purchase another larger rotating assembly and use it as a backup.

How do most of you guys run your engine program for things like this?

Dirt Forum Champ
Total posts: 5390
posted September 15, 2005 04:26 PM  
Along with preventive maitenance on weekly basis, what you can do is once you get 2-3 race nights on your new rings, etc....Use a compression gauge, and mark your psi according to each cylinder. This can be a once a month check up, and When you start to see a large drop in psi then It lets you know if your starting to get blow by. Always do this when motor is warmed up, do to expansion. The more rpms your motor puts out on a weekly basis, the greater the chance for excessive wear.

Dirt Freak

Total posts: 370
posted September 15, 2005 07:06 PM  
1000 laps or so. Look at leakdown %.

Dirt Freak

Total posts: 402
posted September 16, 2005 09:34 AM  
Or like mine, it start's blowing oil outa the breathers. But I only have 1 race left.

James Ott
Dirt Maniac

Total posts: 131
posted September 16, 2005 08:58 PM  
What percentage of leak down do you consider time for a rebuild?

"Winning heals all wounds"

Dirt Freak

Total posts: 205
posted September 18, 2005 01:50 PM  
when warm over 10-12% and start thinkin about it. depending on how aggressive you run it and all. if its under 10.5 you can get away w/ a little more.

I'd be tickled pink to have one stay together long enough to get wore

Dirt Freak

Total posts: 334
posted September 19, 2005 07:56 AM  
Without a sponsor, my motor has to stay together during the year or I have to hang it up until next season. This is the first time I started putting serious money in the engine department and have had to wonder how long the block would be good for. We used to get 3 or 4 races (sometimes just hot laps) before souvenirs would start coming out of the oil pan, taking out the block 9 times out of 10. True example that it comes out to be less expensive to spend a little more when building the motor instead of putting together used junk parts just to get by.

But 1000 laps, that's roughly 28 - 30 races for us...meaning 1 season of racing. I'll show my ignorance in the engine department here...but if you make the pistons and rings a good tight fit when you first build the motor and run it 1 full season, I assume you should be able to clean up the cylinder walls good enough to be able to put a little "wider" ??? set of rings to get one more season out of the block. The following season, you'd then have to bore out that block and find another block to put the good internals you had in. Does this sound right? I'm sure there are many variables to this (from how well your internals are balanced all the way down to how well your air cleaner keeps out the dust particles).

Thanks all

Dirt Forum Champ
Total posts: 874
posted September 19, 2005 08:51 AM  
If you've got a virgin block, or even a .030 block if you work it right and take care of it you can get at least 6 seasons out of it. You can bore all the way up to .060 safely.

Dirt Forum Champ
Total posts: 796
posted September 19, 2005 09:49 AM  
Good paper filters, and regular oil & filter changes you should be able to get by the first year with a slight hone and new rings. Hone it briefly to get a new cross hatch to help seal the rings and your good. Your piston to wall may change .001 to .002 and thats about it.

Next year you might need to go to .040 over, no big deal on a 350 block thou. Use a shelf piston, something that easy to replce, like a 6" rod 383 or something popular so the pistons cost is cheaper than the custom non shelf parts.

The air filter is the key, a K&N on a dusty track all year and you'll need a .030 overbore to clean it up. We change air filters with the oil changes, every 3 weeks. If its major dusty every 2.

Dirt Freak

Total posts: 334
posted September 19, 2005 09:54 AM  
I can see how that could happen, however, what do you do with your rotating assembly that is sitting at .030? Do you buy new pistons and get everything balanced again, using the same block? or Do you find another block and put the rotating assembly into anotehr .030 block? Both involve a bore on the original block, which you could still have sitting around ready to stick a rotating assembly in. I guess it depends on how much you have in the block. If you purchase a new DART block, I would guess would continue to update your rotating assembly.

Really, I'm probably missing the point anyway : ) Usually you don't get the life out of this stuff like I am hoping for. It is nice to hear what others are doing in this area though.

Dirt Freak

Total posts: 334
posted September 19, 2005 10:03 AM  
Krom, you were posting the same time I was.

From advice on here over the winter, when I made my bulk oil, filters, transmission fluid, etc. purchase at he beginning of the year, I went ahead and purchased the same amount of air filters as oil filters. I change every two weeks. If the track wasn't dusty at all, I may let the air filter go another week. I'm too lazy to maintain the K&N properly.

Can someone explain the balancing process of the rotating assembly. Do you treat the crank as one entity? Then the pistons and rods as one entity? Otherwise, if you just keep changing the bore size of the pistons, won't you get your stuff out of balance?

What's a good estimate on the price of a virgin block AND the machine work to have it race prepped?

Dirt Forum Champ
Total posts: 796
posted September 19, 2005 10:32 AM  
You add the weights of the rods, pistons, rings, pin, retainers & and bolts up, and that will give you a bob weight. Then the counter weight is balanced to that number.

Not sure on the perticulars after that, but if you do have to replace the pistons, i believe you could simply weigh each one, and equalize it to the ones in the engine, per hole. A +.010 over piston shouldnt weight to much more.

Good questions thou, maybe someone with more knowledge can answer on the balancing.


Dirt Full Roller

Total posts: 72
posted September 19, 2005 12:24 PM  
with good machine work and good maintenance you should get at least 5 seasons out of a fresh engine , i think the key is to not get em too hot when you boil the coolant out thats when you kill your engine , do a leakdown test at the end of each season and if its still sealed up and you arent getting metal in the filter and oil pressure is consistent to what you have been running , just replace the valve springs and run it again next season , you need to watch the oil filters all season though
this is what i do and yes i have had engines that ran 5 seasons and were running strong when i sold the cars

Dirt Freak

Total posts: 334
posted September 19, 2005 12:38 PM  
I just read up on the whole bobweight deal, but didn't find anything about rebalancing after you bore the motor. The bobweight would change, but it would add the exact same amount of weight to each rod. But it still seems like the crank would need balanced, otherwise, the engine builder wouldn't need your pistons, rods, etc. when they originally balance it. This theory would be more like treating the crank as one entity, neglecting the bobweights.

Equalizing the larger pistons to the weight of the smaller ones could work, but seems like it may be easier to just do the crank without messing with the integrity of the new pistons.

[This message has been edited by dluna (edited September 19, 2005).]

Dirt Maniac

Total posts: 120
posted September 19, 2005 03:16 PM  
To have it done correctly, you would need to have your rotating assembly re-balanced as a unit after going up a size in pistons.

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