Muddywaters

72 LT-1 with a freash complete rebuild. Took the cylinder 30 over so as to true them up. New valves, guides and seats. I installed the engine, started it up so as to break in the cam,(1800 RPM for 20 Min.) I did this with only original exhaust manifolds installed. After run, I blocked the exhaust with rags so air could not get in. I ran the engine a couple more times to adjust idle mixture screws. This weekend I had complet exhaust installed and now see blow by when I remove air cleaner... I removed the filter vent on the drivers side and also get blow by but not as much as the passenger side. Is this correct? Thanks in advance. Don

BigBlockk

This is probably nothing to worry about. You're going to see some vapor. The rings haven't seated all the way yet. Get some miles on it and I'll bet a lot of the blow by goes away.

BigBlockk

Later.....

Muddywaters

Thanks Bigblock, just seems strange the there was no blow by before the mufflers and now there is... I suppose the mufflers put a bit of back pressure on...ummmmm. I suppose it is... more vapor than blow by... thanks for the input!!! Muddy

Cory1970

I wouldn't worry about it. Take it easy on the motor for the a while, at least 500+ miles. Do not abuse the motor untill it is broken in. The rings need time to seat, so stay away from red line. A mixture of city and highway driving is fine, just not too much of either.

I would expect blow by for at least 500 to 3k miles. Most people are down a quart of oil by the first oil change, so keep an eye on it. New cars even experience blow by at first.

what oil are you using?

Muddywaters

Cory1970 thanks for the input... I put Havaline 30 wt. I'm still about 3months away to getting it out there on the road, for the break in. I'm just putting the dash together, then paint and finally the interior.

sweethence

Definately needs more breaking in, 500 miles is the rule of thumb, but also break the motor in how you going to drive it. I recommend a few nice long 100 mile cruises under 60 on the highway, as well as around town for a good break in. then change the oil afetr the first 500 miles and check it closely for shavings and such. Dont sweat the blowby for now. but after break in run a compression test, or better off a leakdown test to settle the issue in your mind




Tim

Muddywaters

Thanks guys, feeling much better...Sweethence, I like the idea of the leakdown test...Thanks Don

sweethence

No sweat, ive rebuilt / broken in a number of motors, liek said earlier, just monitor your oil consumption (hopefully none), oil pressure, operating temp, water level, during the break in process.

happy motoring


Tim

lars

That's not what you want to do to get those rings to seat. The ring manufacturers recommend that you put the cylinders under high load as soon as possible after cam break-in. Do not *****-foot the motor: As soon as you have the 15-20 minute cam break-in done, get the car out and give it several hard WOT runs through 1st and second gear. You don't need to hit redline, but you need to create peak cylinder pressure. This will force the rings into the cylinder walls and will make them seat instantly. If they don't seat right away in this fashion, you stand the risk of glazing the cylinders with the result that the rings will never seat. Once you've done the WOT ring seat, there is no further "break-in" required. So get the car out and hammer it.

bashcraft

This is exactly what my engine builder told me.

PNK

I have to agree with Lars here, if it was true that you needed to go easy on the engine for a perfect break in, then dynopulls on new engines would be a deathsentence even thou every respected engine builder out there does a dynopull on a new engine to both break it in and to also look for possible failures.

precisely as Lars said "take it out and hammer it" was the instruction i got with my latest engine build.

neoh77

Amen....it's the only way to break in motorcycle engines too.

Controversial, but I follow it:
http://www.mototuneusa.com/break_in_secrets.htm

SanDiegoPaul

Yep The 500 mile rule is old school and also, for engines that are not bored. If the cylinder is cleaned up by boring, and of course the pistons will be new too, there's nothing to be gained by going easy on it (if the rings have been fitted properly).

My stroker saw the redline the day after I built it. That was the day after Christmas of '03. We isntalled it on Christmas day, broke in the cam, and I drove it about 25 miles that day before we called it quits...it was Christmas after all!

Now she's got about 15K miles on her and trust me, it has never EVER missed being 'broken in' like we used to do.

big_G

Ahhh, my kind of thinking...

Muddywaters

Well, did exactly what Lars and most said... OMG! This puppy is fast and pulls very strong! Thanks Lars, and thanks again for the distributer work. Don

James B

that is one great looking engine compartment man. that carb looks SOO much better than my 30 year old Q jet.

Cory1970

Interesting, after a little reseach I agree. Thanks for the info lars.

As far as blow by goes, I still would expect it for 500- 3k miles.

Muddywaters

Thanks James... actually that carb is dated Feb. 72!!! I had a real nice guy in MO. restore it for me. As you can see, he did a great job. He only does Holley's but, his son does Quad's. If you need his info. give me a shout.