Heat Cycling Big Bore Install
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,936
Likes: 8,036
From: poway
Build up is probably the wrong word, more like deposits, my fault. Though yes, the top outer edge of the piston and the very small gap around the cylinder head gasket where they mate up with the cylinders. Not allowing that to build up can create small hot spots on the sides of the pistons. Also the beneficial deposits around your ring gaps that can help promote the rings sealing against the walls.
We definitely aren't talking about a lot of deposits, very little in fact.
I know it's not apples to apples but in the 2 stroke world it's called piston wash, if you ever pulled a head and didn't have carbon build up in the center of your piston it was a tall tell sign you are running too rich. When you are jetted properly a pattern will start to develop where the intake and exhaust ports are at. A really experienced mechanic or tuner can use that to know exactly what the carbs are doing if the motor is otherwise healthy.
We definitely aren't talking about a lot of deposits, very little in fact.
I know it's not apples to apples but in the 2 stroke world it's called piston wash, if you ever pulled a head and didn't have carbon build up in the center of your piston it was a tall tell sign you are running too rich. When you are jetted properly a pattern will start to develop where the intake and exhaust ports are at. A really experienced mechanic or tuner can use that to know exactly what the carbs are doing if the motor is otherwise healthy.
On the motors I've disassembled, I've not seen buildup on the ring ends.. I have burned them with too much fuel and timing tho..
I would think that detergents in the gasoline would have more effect..
Been years since I messed with 2 smokes but I would think that lack of carbon buildup in the chamber would be due to too rich of a oil to fuel mixture and not AFR.
Road Master
Joined: Nov 2023
Posts: 972
Likes: 1,016
From: Knoxville
On my last two builds, I used Hammers procedure and both motors run well and dont use a drop of oil. Living on a massive hill helps with decel sealing.
One question I have is on the lifters. I didnt install new lifters on either one of my builds. In my auto days wed grab a primer spin the oil pump until we had flow out of the pushrods to the rockers and adjust. Is it worth the time to let them sit in oil, perhaps a sealed jug with a vacuum? Adjusting preload correctly before starting is the primary concern.
The start up of my build is a ways away, planning on spending some time watching Mr. Baxter and Hammer Dan to catch some insights.
One question I have is on the lifters. I didnt install new lifters on either one of my builds. In my auto days wed grab a primer spin the oil pump until we had flow out of the pushrods to the rockers and adjust. Is it worth the time to let them sit in oil, perhaps a sealed jug with a vacuum? Adjusting preload correctly before starting is the primary concern.
The start up of my build is a ways away, planning on spending some time watching Mr. Baxter and Hammer Dan to catch some insights.
Intermediate
Joined: Aug 2024
Posts: 44
Likes: 26
From: Oklahoma
Build up is probably the wrong word, more like deposits, my fault. Though yes, the top outer edge of the piston and the very small gap around the cylinder head gasket where they mate up with the cylinders. Not allowing that to build up can create small hot spots on the sides of the pistons. Also the beneficial deposits around your ring gaps that can help promote the rings sealing against the walls.
We definitely aren't talking about a lot of deposits, very little in fact.
I know it's not apples to apples but in the 2 stroke world it's called piston wash, if you ever pulled a head and didn't have carbon build up in the center of your piston it was a tall tell sign you are running too rich. When you are jetted properly a pattern will start to develop where the intake and exhaust ports are at. A really experienced mechanic or tuner can use that to know exactly what the carbs are doing if the motor is otherwise healthy.
We definitely aren't talking about a lot of deposits, very little in fact.
I know it's not apples to apples but in the 2 stroke world it's called piston wash, if you ever pulled a head and didn't have carbon build up in the center of your piston it was a tall tell sign you are running too rich. When you are jetted properly a pattern will start to develop where the intake and exhaust ports are at. A really experienced mechanic or tuner can use that to know exactly what the carbs are doing if the motor is otherwise healthy.
Seasoned HDF Member
Joined: Mar 2021
Posts: 18,471
Likes: 3,723
From: backwoods
Breaking in engines, is an age old debate. For me, I don't think it hurts to heat cycle. I am not racing and in no rush. Maybe it doesn't do any good.
Seasoned HDF Member
Joined: Dec 2010
Posts: 7,736
Likes: 1,524
From: Coromandel Peninsula New Zealand
You have more experience, and maybe right. But if you are constantly rebuilding, do you care about burning a little oil?
Breaking in engines, is an age old debate. For me, I don't think it hurts to heat cycle. I am not racing and in no rush. Maybe it doesn't do any good.
Breaking in engines, is an age old debate. For me, I don't think it hurts to heat cycle. I am not racing and in no rush. Maybe it doesn't do any good.
That would be my professional opinion and possibly that of many other professional wrenches. I can guarantee you that brand new Harleys are not heat cycled like that in the factory and never have been.
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Club Member
Joined: Apr 2011
Posts: 5,817
Likes: 7,850
From: SE Louisiana
One question I have is on the lifters. I didnt install new lifters on either one of my builds. In my auto days wed grab a primer spin the oil pump until we had flow out of the pushrods to the rockers and adjust. Is it worth the time to let them sit in oil, perhaps a sealed jug with a vacuum? Adjusting preload correctly before starting is the primary concern.
Use a few drops of oil to assemble them, but leave then empty.
Before you install the top rocker covers is a good time to adjust pushrods and prime the oil system.
It's easy to see where zero lash is and no wait for bleed down after adjustment with empty lifters.
Then prime the oil system, spin the engine with the plugs out until you see oil coming out the rockers, and make sure the oil gets to the valve stems.
Don't kill the starter, you may have to let it cool a time or two before all rockers have oil coming out.
You should have previously removed shafts and clean the inside of rockers and make sure oil holes are clean.
Finish engine assembly, it's ready tp go.
Seasoned HDF Member
Joined: Mar 2021
Posts: 18,471
Likes: 3,723
From: backwoods
There are some that say do not heat cycle at all, the instructions that say use a stopwatch and do 10-second, 20-second etc heat cycles seems just a very good way of avoiding owner-installed warranty claims as nobody will do it that way and they can say you didn't follow the instructions to the second and so "sorry, out of warranty parameters at install".
That would be my professional opinion and possibly that of many other professional wrenches. I can guarantee you that brand new Harleys are not heat cycled like that in the factory and never have been.
That would be my professional opinion and possibly that of many other professional wrenches. I can guarantee you that brand new Harleys are not heat cycled like that in the factory and never have been.
As far as assembly, coat with oil, dry metal and metal is bad. As said pull plugs and turn over.
Last edited by Rounders; Oct 9, 2024 at 07:15 AM.