That's pretty conclusive.

So neal, here is my questions on the vacuum port theory of yours... So what you are saying is that all engines with open vacuum port, in theory should all be done in about 2 gallons of fuel? Based on your theory there is no way they can last more than that under dusty conditions.I think the bearing will die early, like I said before,I dont think that much dirt can go thru the engine to make it fail early.Are you saying that all that dirt goes in through the open vacuum port or the front of the crank.If that was the case the oil and dirt would've plugged that hole very fast.If it was the front of the crank,you would see scratched marks on the front part of the crank like you see in a crank window when a filter fails.

My question is, why do the companies put those vacuum ports there in the first place? Honest question, what is the "purpose" for them?

seems like its Open season on Clockwork... dang

That's usually what happens when people are getting beat by an "engine, car" it seems like. All the haters find something to put it down to make them feel better.

Th engines aren't always affected just from running in dusty conditions..... We have seen engines with open vacuum ports last gallons with no bearing issues, however we have also seen engines pack up with dirt on the first tank of fuel ( 17011 Nova bearings no less ) ... My best guess is the biggest issues show up when a engine is coming off wide open throttle to closed throttle...engine RPM Is high, but carb gate is closed.. this is when the engine has the highest case vacuum and when the dirt is most likely to be ingested....So the frequency of the engine bearings filling with dirt likely has to do with the frequency of coming off throttle while in a dust cloud

As for the volume of dirt, I will post pictures and let you be the judge...IMO more then enough dirt gets in to do damage. and we definitely see markings from it.... One thing to consider however is dirt that comes thru the bearing tends to be finer then the dirt that comes thru the airfilter..the front bearing acts like a grinding mill and pulverizes any dirt into a lapping paste before it makes its way thru.....

In the end the results of blocking the byapass have been more then conclusive...I have opened and changed bearings on hundreds of engines both with the bypass open and the bypass blocked and there is no comparison between them....Engines with the blocked bypass have much longer bearing life and far less dirt inside and behind the bearing...The only side effect is the engines will leak a tad more........ Also engines with the bypass blocked are far more resistant to stalling by the brake cleaner test.... I have explained this a hundred times over, either you believe me or you don't..If you think I would lie or be mistaken about something so obvious and easy to distinguish then so be it...... But anyone who's spent any time in my shop watching me pull down engines will know how through and methodical I am ..

How many here can say they have changed hundreds of bearings, and not only changed them but taken the time to use Nitro spray and white glove test the bearings over paper to see whats inside of them.... I have done this hundreds of times over the last 3 years and know for sure without any question or doubt that blocking that bypass eliminates the engine sucking up dirt into the bearing......

The engine have the bypass to prevent fuel from leaking... issue is the bypass is sometimes too effective, or sized incorrectly for the fuels viscosity...This creates excess vacuum behind the bearing which causes dirt to get sucked inside.... doesn't happen all the time, but it does happen...if any of you had the hands on with the number of engines that I do you would see this exactly as I do....In a good week I will handle more engines then many here have handled their entire RC career....So obviously I am going to see things and patterns that the average hobbyist is likely not going to see.....

In the end I have nothing at all to gain by telling anyone this...If anything sharing this information works against me... So believe you me, I am dam sure of my findings for me to be willing to stick my neck out like I am ....

I agree with the fact that when at full throttle high rpm the closed throttle there is a major vacuum affect on the front bearing. But my thoughts here, is the bypass port is just the path of least resistance, when the vacuum occurs. By plugging this port you eliminate that path, but the vacuum isn't eliminated. So now it has to pull air from other areas. So with the front bearing being the week point with the unplugged port wouldn't it still be just as week with the plugged?

Maybe with it plugged the vacuum spike is not as aggressive. Just throwing some ideas at you.

it doesn't have to pull air in necessarily...by blocking the bypass we increase the amount of fluid in the nose of the engine helping to better seal itself..

regardless my only concern was to stop the engine from ingesting dirt...for a while there we seeing a good number of engines packing up with dirt and blocking the bypass was one of the things I found that worked to combat it...

And no the port does not plug up, the fluid transfer seems to keep it quite cleaned out .( Someone asked me this earlier )

Max,

For someone that isn't new to nitro, but new to 1/8th scale racing, would you suggest motor teardown at periodic points in the life of the engine to ensure the front bearing is relatively clean and the motor isn't ingesting dirt to the point of the pictures above?

I haven't ran outdoors yet, so I haven't experienced the "oh my god my car is covered", but with my gallon old bluehead OS 21 Max it's only seen indoor dusty conditions. Should I be looking for internal wear at this point?

I am a believer in learning how to properly maintain a nitro engine...without question it is a good idea to periodically tear down and inspect your engine...Sometimes you can run for many gallons without a hitch, other times you can lose a engine in one day...

We tear up our engines for the pure pleasure of doing it . This maintenance is also a reason why I restarted nitro, I missed the mechanical beauty of nitro engines.

When I restarted nitro this year many drivers told me not to open the engine because it needs a particular attention blablabla but I can't help it and do it every 2 races or so. It could be a placebo effect but I felt a clean engine works better too. Once I had a problem with the engine not perfectly working and couldn't solve this by tuning.. cleaned it and it ran perfectly again

when I read this thread I realise it would be great to post a tutorial about how to determine the level of wear from each part of a nitro engine based on pictures for example... if I had enough knowledge I would do it but I'm a beginner

nitro would benefit from real "how to" subjects

hey great input in this thread btw i feel he knows what he talks about.

just a quick question i have an old os xzb engine that i was using one of those plastic bearing covers which ran for quite a few litres of fuel.

it still has alot of compression.

and the engine high revs after wide open throttle.

so i checked it as i was running the engine without the plastic cover on it and did the soap bubble leak test it has air coming from the front bearing.

do i need to replace the bearing to have an airtight seal or would running the cover with enough grease fix it?

any reply is much appreciated. thankyou.

I'll accept that. It was just what came to my mind, wanted to bounce it off you.

When an engine runs on (high rev) after a full throttle pull it is usually indicative of a lean condition on the HSN. I would investigate that before I did any tear down.

Just finished up initial break in of the 5TR (4 WOT runs on the starter box) and disassembled for inspection. Everything looks pretty good.

Clutch shoes collected quite a bit of oil


Front bearing has considerably less oil on it than the B6 Pro I broke in using the same method a month or two ago (didnt preheat that engine but doubt that had much to do with it).


Love this head button (probably spendy to replace ).


Nothing unusual here.


Plug looks pretty good.


Nice a clean down here as well.


No surprises


Crank is nice a clean with no grooves anywhere.


Bearings are covered well


Sleeve looks good


Tiny nick in the finish of the back plate (left of center)


I'll take it down to the track this week and begin leaning it out over the course of another 1/2 gallon of fuel (hair less than a quart through it right now).