Go Back  RCU Forums > RC Airplanes > Questions and Answers
Reload this Page >

Interference Engines

Notices
Questions and Answers If you have general RC questions or answers discuss it here.

Interference Engines

Old 05-07-2011, 12:10 AM
  #1  
JollyPopper
Thread Starter
My Feedback: (6)
 
JollyPopper's Avatar
 
Join Date: Oct 2002
Location: Mountain Home, AR
Posts: 2,684
Likes: 0
Received 0 Likes on 0 Posts
Default Interference Engines

Some automobile engines are interference engines. That is, if the engine is far enough out of time (belt breaks) the pistons can bend the valves. Are our four cycle RC engines like this, or will the valves clear the piston no matter where the timing is? Just wondered.
Old 05-07-2011, 12:22 AM
  #2  
bartman77
Junior Member
 
bartman77's Avatar
 
Join Date: Dec 2010
Location: central coast, AUSTRALIA
Posts: 7
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Interference Engines

hi the only way i know that a valve may get bent or put through a piston is if the gears are missaligned as the cam is gear driven ,
Old 05-07-2011, 08:23 AM
  #3  
ChuckW
Senior Member
 
ChuckW's Avatar
 
Join Date: Jun 2006
Location: Clovis, CA
Posts: 5,165
Likes: 0
Received 1 Like on 1 Post
Default RE: Interference Engines

I have never had to find out. Even if there was a chance of valve to piston contact, the camshaft would have to be installed way out of time for it to happen or a cam gear would have to break while running. I also wonder if the skinny pushrods would bend first on an RC engine? Regardless, not likely to ever be an issue.
Old 05-07-2011, 08:34 AM
  #4  
SeamusG
Senior Member
 
SeamusG's Avatar
 
Join Date: Jun 2007
Location: Arvada, CO
Posts: 3,919
Likes: 0
Received 1 Like on 1 Post
Default RE: Interference Engines

The only "interference" reference to 4 stroke RC engine I can find is interference between the engine and the Rx.

Like Bartman implied - no belts to break between the crank and the overhead cam so you won't have any problems with catastrophic failure of the belt while running. IF the engines are truly of interference type AND you think you may blow the static setup so bad that when you try to start it up the valves will hit the piston - THEN - have someone else do the rebuild for you. Recognize your limitations BEFORE you exceed them.

Just sayin' ...
Old 05-07-2011, 06:48 PM
  #5  
JollyPopper
Thread Starter
My Feedback: (6)
 
JollyPopper's Avatar
 
Join Date: Oct 2002
Location: Mountain Home, AR
Posts: 2,684
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Interference Engines

I have been properly chastised. I promise never to do it again.
Old 05-07-2011, 07:17 PM
  #6  
SeamusG
Senior Member
 
SeamusG's Avatar
 
Join Date: Jun 2007
Location: Arvada, CO
Posts: 3,919
Likes: 0
Received 1 Like on 1 Post
Default RE: Interference Engines

Em - Jolly - not chastised - only a friendly harassment (the wink-wink nudge-nudge smiley face).

I'm familiar with OHC auto engines that are classified as interference/non-interference. Warning to be very aware of the timing belt replacement interval. But our 4 stroke RC engines have OHV with pushrods. I don't recall hearing any "cautionary" heads up on OHV auto engines in my short 60 years. Is it of concern for an automotive OHV engine? Thinking that the same issue would be in play with OHV auto engines - make sure you have the static cam timing (chain) right before turning the engine over.

At least with Saitos - the cam is driven by big ole gear up front that engages the crank rather than a timing chain. You can easily blow the timing by a tooth. There's a bunch of decent threads that include good tutorials for setting the cam / crank timing.

Things that make ya go 'emmmmmm ...."


Old 05-07-2011, 07:40 PM
  #7  
JollyPopper
Thread Starter
My Feedback: (6)
 
JollyPopper's Avatar
 
Join Date: Oct 2002
Location: Mountain Home, AR
Posts: 2,684
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Interference Engines

I knew that. I think I knew that. Yes, I too am familiar with automobile OHV engines. I have seen firsthand what happens when a belt breaks in an interference engine running 3,000 RPM or so. And I was just sitting here gazing into space and it popped into my head: what would happen in an RC engine if the cam gear were installed with the dot at 3 or 9 instead of 6 or 12. I have no intention of finding out up close and personally. I just thought somebody might know. It's really not very important in the grand scheme of things. No offense was taken. I was simply pushing your buttons.
Old 05-07-2011, 07:44 PM
  #8  
ChuckW
Senior Member
 
ChuckW's Avatar
 
Join Date: Jun 2006
Location: Clovis, CA
Posts: 5,165
Likes: 0
Received 1 Like on 1 Post
Default RE: Interference Engines

I thought I remembered seeing an RC engine with a timing belt somewhere so I did a search and found this:

http://www.rcuniverse.com/forum/m_10...m.htm#10100630

Looks like it uses an overhead rotary valve system though and not an overhead camshaft.
Old 05-07-2011, 07:45 PM
  #9  
JollyPopper
Thread Starter
My Feedback: (6)
 
JollyPopper's Avatar
 
Join Date: Oct 2002
Location: Mountain Home, AR
Posts: 2,684
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Interference Engines

Oh, I remember what prompted my curiosity. Somebody in another thread advised installing the cam gear with the dot at 5 o'clock, and I idly wondered if someone were to do that, just how close is that to getting the valves to kiss the piston? And then wondering if kissing the piston in an RC engine was even possible. Thus the post.
Old 05-07-2011, 07:52 PM
  #10  
Gray Beard
My Feedback: (-1)
 
Join Date: Apr 2003
Location: Hemderson, NV
Posts: 14,385
Likes: 0
Received 3 Likes on 3 Posts
Default RE: Interference Engines

Very cool stuff Chuck. I have a photo in an old High Flight with a four stroke with a roots type blower on it. I think the photo said it was an OS but it sure looked Saito to me.
Old 05-07-2011, 08:28 PM
  #11  
Tired Old Man
Senior Member
My Feedback: (1)
 
Join Date: Feb 2002
Location: Valley Springs, CA
Posts: 18,602
Likes: 0
Received 1 Like on 1 Post
Default RE: Interference Engines

It was an OS.
Old 05-07-2011, 08:51 PM
  #12  
jamesc43
Senior Member
My Feedback: (2)
 
Join Date: Jun 2003
Location: Colorado Springs, CO
Posts: 355
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Interference Engines

I recall some of the GM (Chevy V-8) engine ran a plastic outer ring on the cam gear and the cam gear was driven by a rather cheap
inexpensine chain. I not that familiar with the Ford or Chrysler products. At times, there could be problems with the cam chains jumping
teeth or stipping the cam gear. I can see during these conditions and interference engine could get damaged while running.

If this type of thing happened to our RC engine, I would think there would be more issues than just the piston/valve clearance.

James
Old 05-08-2011, 04:24 AM
  #13  
JohnBuckner
My Feedback: (1)
 
JohnBuckner's Avatar
 
Join Date: Dec 2001
Location: Kingman, AZ
Posts: 10,441
Likes: 0
Received 1 Like on 1 Post
Default RE: Interference Engines

ORIGINAL: ChuckW

I thought I remembered seeing an RC engine with a timing belt somewhere so I did a search and found this:

http://www.rcuniverse.com/forum/m_10...m.htm#10100630

Looks like it uses an overhead rotary valve system though and not an overhead camshaft.

My Webra T4-60 although it too is an overhead rotary valve and not poppets it is a belt drive though. I beleve there was a T4-90 also. Last flew it in a Busa Bristol M-1 kit.

John
Attached Thumbnails Click image for larger version

Name:	Sq45659.jpg
Views:	16
Size:	65.9 KB
ID:	1605712   Click image for larger version

Name:	Hc94203.jpg
Views:	18
Size:	65.9 KB
ID:	1605713   Click image for larger version

Name:	Fk16071.jpg
Views:	21
Size:	65.2 KB
ID:	1605714   Click image for larger version

Name:	Xv65674.jpg
Views:	18
Size:	237.9 KB
ID:	1605715  
Old 05-08-2011, 07:36 AM
  #14  
Gray Beard
My Feedback: (-1)
 
Join Date: Apr 2003
Location: Hemderson, NV
Posts: 14,385
Likes: 0
Received 3 Likes on 3 Posts
Default RE: Interference Engines

Very cool John!!! Never seen anything like it before. I have seen a lot of different engines that have been tried in modeling over the years but there were a lot of strange ideas that never caught on that I don't even see in magazines. I need to find a book showing these different engines. Once in a while someone will show something like yours on RCU but not often enough. Really Really Cool!!!!!!!!!!!
Old 05-08-2011, 09:35 AM
  #15  
ChuckW
Senior Member
 
ChuckW's Avatar
 
Join Date: Jun 2006
Location: Clovis, CA
Posts: 5,165
Likes: 0
Received 1 Like on 1 Post
Default RE: Interference Engines

Sometimes I think just the engines themselves are more interesting than the airplanes. Have you ever gone on youtube and looked at some of the miniature engine videos? There are people building tiny flat-head Fords, V-12's, you name it. Very cool stuff.
Old 05-08-2011, 09:47 AM
  #16  
Gray Beard
My Feedback: (-1)
 
Join Date: Apr 2003
Location: Hemderson, NV
Posts: 14,385
Likes: 0
Received 3 Likes on 3 Posts
Default RE: Interference Engines

Yes, I get sent a lot of that stuff. One friend in NY has a fellow club member you sometimes see in scale magazines, he is a master machinist and not only designs and builds some of the best giant scale WW1 planes I have ever seen, he also makes the scale engines, the real deal!! I belong to a wood working club and one of the guys used to own a machine shop. He has built a couple of working steam engines from wood, all hand turned on the lathe and work on compressed air.
I have seen magazines of older engines but I would like to find one showing some of the engines like the one John has that we don't see often. There have been a lot of them tried and just never caught on. I have one book about planes calle The Wrong Stuff, some good ideas but for one reason or another weren't needed or were too advanced for there time.
Old 05-08-2011, 09:54 AM
  #17  
Gray Beard
My Feedback: (-1)
 
Join Date: Apr 2003
Location: Hemderson, NV
Posts: 14,385
Likes: 0
Received 3 Likes on 3 Posts
Default RE: Interference Engines

Chuck, I forgot to mention this, The IMAA Mini Fest will be held at Castle Air Base May 26-29. It's now called the Mini Fest because for a while we no longer had Castle as a venue so the event got smaller while the club was trying different places. It's back at Castle but word got out and a lot of the old pilots started showing up again and it's getting bigger again!! Should be a good show again this year. They had {from what I was told} over 100 pilots last year.
Gene
Old 05-08-2011, 01:21 PM
  #18  
JohnBuckner
My Feedback: (1)
 
JohnBuckner's Avatar
 
Join Date: Dec 2001
Location: Kingman, AZ
Posts: 10,441
Likes: 0
Received 1 Like on 1 Post
Default RE: Interference Engines

Thanks GB indeed model engines are interesting. That Webra was a contemperary of the Saito .45 but somehow it was very lethargic especially when compared with a fourstoke .60 OS. least that was my perception of it.

It flew that Bristol very poorly you know whats the word? Prototypically, gotta love that word I later replaced it in the Bristol with a Magnum .80 (another orphaned engine) and it came alive and enjoyable for several more years untill I did something stupid RIP.

You got me fired up and I made another set of pics that I wanted to show comparing the Webra T4-60's carburator throat right next to the venturi of Contemperary Saito .45s carb throat. The Saito's is darn near twice the throat volumn.

Hmm suppose this has got something to do with the Webra being so weak or at least a part of it?
Ah Ha I'd bet that also has sumptin to do with the webra starting and running so easy. Heck maybe it was so darn smooth because of a lack of all that reciprocating mass.

I agree with you chuck just about every engine imaginable has been homebuilt by folks with extrodianry skills, they are amazing.

Sorry for the hijack JollyPopper, Oh don,t ever stop being curious its what keeps us alive[8D]

John

Oh that big hole at the top of the webra in the back is the exhaust port and you can see the valve can in there. A large threaded disc threaded in the big hole and it had a tiny little exhaust pipe.
Attached Thumbnails Click image for larger version

Name:	Nl30896.jpg
Views:	16
Size:	65.3 KB
ID:	1605854  
Old 05-08-2011, 03:34 PM
  #19  
Srewinkel
Member
 
Join Date: Aug 2009
Location: goodyear, AZ
Posts: 84
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Interference Engines

I had the c-clip that holds the valve keeper in place break on a ys-120. Happened at WOT. dropped the exhaust valve, piston smacked it.  Valve stem bent as well as the pushrod.  Put a nice dent in the top of the piston.

I knew something bad happened because the engine just spun down freely. Luckily was high enough to land dead stick.  

If you really want to know if your rc engine is interference type, find the volume of the combustion chamber with piston at TDC and figure out how far the valves open.

I find it curious that as popular as RC engines are, why can you not by high performance camshafts, maybe changing duration and lift to get better output at different RPMs.  I think would be cool for 3D flying as the throttle position is changed all the time.  hmmmm. if only i had unlimited funding to start selling tiny camshafts.. lol
Old 05-08-2011, 04:30 PM
  #20  
fred985
Senior Member
 
Join Date: May 2007
Location: stony point, NY
Posts: 290
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Interference Engines

i had a lincoln with a 351 that striped the plastic timing gear. the cam stoped an so did the engine. no harm 2 the valves but it got a solid steel set of timing gears that were made for the hy prof mustng 351 windsor engine.
Old 05-08-2011, 04:40 PM
  #21  
crossman
 
Join Date: Jun 2007
Location: Grand Blanc, MI
Posts: 536
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Interference Engines

The simple way to see if an engine would have a clearance issue would be to hold a valve open and VERY slowly turn the crank. If you can turn a complete revolution without touching the valve, there is no interference. If there is a problem, it would occur if the cam somehow stopped turnning, slipping a few teeth would probably not be enough for anything to come into contact. The only failure that would cause interfernce would be if the cam somehow stopped turning completely with a valve open. With a direct gear cam drive (no belt or chain) that doesn't seem like the most likely situation.
Old 05-08-2011, 06:55 PM
  #22  
SeamusG
Senior Member
 
SeamusG's Avatar
 
Join Date: Jun 2007
Location: Arvada, CO
Posts: 3,919
Likes: 0
Received 1 Like on 1 Post
Default RE: Interference Engines


ORIGINAL: crossman

The simple way to see if an engine would have a clearance issue would be to hold a valve open and VERY slowly turn the crank. If you can turn a complete revolution without touching the valve, there is no interference. If there is a problem, it would occur if the cam somehow stopped turnning, slipping a few teeth would probably not be enough for anything to come into contact. The only failure that would cause interfernce would be if the cam somehow stopped turning completely with a valve open. With a direct gear cam drive (no belt or chain) that doesn't seem like the most likely situation.
Question:How do you hold the valve open to the max lift of the cam? Anything more "open" than that will only demonstrate that at "valve train total catastrophic failure" the piston will or won't hit the fallen valve. Some builders use a bit of modeling clay skinned on to the piston top to check for valve / piston clearance. Obviously, this requires several disassembly/assembly sequences.

Other than mismatching the gears on a typical OHV4 stroke, a push rod may not be totally seated into the cup in the lifter (at the cam lobe) or the cup in the rocker arm. If either of these conditions exist, the valve will be excessively extended into the combustion chamber and may ding the piston top. Pushrod wear will only shorten the rod reducing the valve lift.

Em, enquiring minds wonder - at what RPMwill the typical 4 stroke "float"the valves?

Old 05-09-2011, 10:16 AM
  #23  
crossman
 
Join Date: Jun 2007
Location: Grand Blanc, MI
Posts: 536
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Interference Engines


ORIGINAL: SeamusG


ORIGINAL: crossman

The simple way to see if an engine would have a clearance issue would be to hold a valve open and VERY slowly turn the crank. If you can turn a complete revolution without touching the valve, there is no interference. If there is a problem, it would occur if the cam somehow stopped turnning, slipping a few teeth would probably not be enough for anything to come into contact. The only failure that would cause interfernce would be if the cam somehow stopped turning completely with a valve open. With a direct gear cam drive (no belt or chain) that doesn't seem like the most likely situation.
Question: How do you hold the valve open to the max lift of the cam? Anything more ''open'' than that will only demonstrate that at ''valve train total catastrophic failure'' the piston will or won't hit the fallen valve. Some builders use a bit of modeling clay skinned on to the piston top to check for valve / piston clearance. Obviously, this requires several disassembly/assembly sequences.

Other than mismatching the gears on a typical OHV 4 stroke, a push rod may not be totally seated into the cup in the lifter (at the cam lobe) or the cup in the rocker arm. If either of these conditions exist, the valve will be excessively extended into the combustion chamber and may ding the piston top. Pushrod wear will only shorten the rod reducing the valve lift.

Em, enquiring minds wonder - at what RPM will the typical 4 stroke ''float'' the valves?


I would have to admit that I haven't thought this exercise through completely. The clay on the piston did occur to me, but that would be be, as you mentioned, very time comsuming, particularly on a Saito, where the head is not separate ftom the cylinder. I 'm guessing that some sort of fixture would have to be created to hold the valve at the proper open distance.

I also remember having a Pontiac with a OHV 4cylinder about 20 years back that was listed as being an "interference engine" in the service books. I had 2 timing belts fail with no apparent internal damage to the engine. As I recall, both times the teeth stripped off the belt, so the cam did not stop, it just put the engine greatly out of time.


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.