LocostUSA.com

Learning how to build Lotus Seven replicas...together!
It is currently March 29, 2024, 3:27 am

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 22 posts ]  Go to page Previous  1, 2
Author Message
PostPosted: July 13, 2018, 6:42 pm 
Offline
User avatar

Joined: April 26, 2008, 6:06 pm
Posts: 3268
Location: Under the weather. (Seattle)
You'll never get great performance, let alone the magical combination of great performance and great economy we enjoy today, out of a non-interference engine. Consider that even many (most?) applications of the venerable SBC and SBF engines were interference.

_________________
-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie


Top
 Profile  
Reply with quote  
PostPosted: July 13, 2018, 8:22 pm 
Offline
User avatar

Joined: July 17, 2008, 9:11 am
Posts: 6414
Location: West Chicago,IL
Driven5 wrote:
You'll never get great performance, let alone the magical combination of great performance and great economy and great emissions we enjoy today, out of a non-interference engine. Consider that even many (most?) applications of the venerable SBC and SBF engines were interference.


FIFY

I agree.

I've never had a belt or chain break. I have had a chain skip a cog on a ford 289 back in the day. Chains are not a scheduled maintenance item like belts are. That says something about their relative life / reliability IMO.

_________________
Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766


Top
 Profile  
Reply with quote  
PostPosted: July 14, 2018, 7:06 am 
Offline
Automotive Encyclopedia
User avatar

Joined: December 22, 2006, 2:05 pm
Posts: 8037
A modified sbc or sbf may be interference but that has not been my experience. Many years ago, oem pushrod chain system failures (not to be confused with Carguy123 reference to sohc/dohc chain systems) were designed into the cam gear through the use of plastic and or aluminum gears meant to last long enough for the warranty to run out, encouraging the owner to buy another vehicle rather than repair. I’ve had one cam gear failure on an sbc but had no valve to piston contact. Replacement timing sets have steel cam gears or double roller chains for more accurate timing at high rpm that I’ve never seen fail.

Oil leaks can soften a timing belt, shortening the life of the rubber teeth which are what fail. Improper handling by flexing the new belt inside and out can start the cracks that eventually lead to failure, along with forceful installation from not having the right tools to hold the cams in position to change a belt. Applications where the coolant pump is driven by the timing belt have a much shorter life and can 0have trouble meeting the published service interval while sohc belts seem to live forever. Sohc engines are often non-interference.

The performance gain of interference and reduced parasitic loss with a belt is hardly worth the damage that can be done, like any reduced margin for error such as designing for minimal fastener size/strength and minimal weld area placed in tension to save a few ounces here and there or running a light because you can get away with it most of the time.
I’ve had efi as well as carb tuners make my eyes water from their attempts to make more power. If it works well, leave it alone, please. It is a compromise.

I get Richards point that whatever donor you choose, if the drivetrain production run is only a few years, get spares now if you intend to keep it forever. There are few engines that do not have adequate power for a locost owner to be written up for reckless operation on a public road, so who are we trying to impress?

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12


Top
 Profile  
Reply with quote  
PostPosted: July 14, 2018, 11:24 am 
Offline
User avatar

Joined: April 26, 2008, 6:06 pm
Posts: 3268
Location: Under the weather. (Seattle)
Just because a catastrophic timing failure doesn't result in any obvious signs of piston to valve contact, does not in and of itself mean it is a non-interference engine. Mild interference, where there is a good chance no cylinder will have a valve extended far enough during a catastrophic timing failure to make contact as the pistons pass TDC or that interfere primarily under the deformations of higher dynamic loads, is still interference. Plenty of people both have, and have not, had piston-valve contact on their completely stock SBC's and SBF's when their timing gear or chain let loose. The lowest performance 'truck' type applications may have more commonly been true non-interference, but most applications with any attempt at a decent performing cam (stock or aftermarket) will most likely at least technically be interference. As with so many things, there are varyng degrees of interference. So the greater the performance gets, the more severe the potential interference. Right up until you have valve reliefs and cans opening to follow those reliefs as closely as possible.

_________________
-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie


Top
 Profile  
Reply with quote  
PostPosted: July 14, 2018, 12:54 pm 
Offline
Automotive Encyclopedia
User avatar

Joined: December 22, 2006, 2:05 pm
Posts: 8037
Point taken, but the term interference or non has to do with the likely hood of damage.
You've made a great point in that preventing a timing failure is important, engine type notwithstanding.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12


Top
 Profile  
Reply with quote  
PostPosted: July 15, 2018, 2:25 pm 
Offline

Joined: January 31, 2008, 5:34 pm
Posts: 781
Location: SW Wes Consin
I have an interference engine (Yaris) and when I took it in for a new timing belt my mechanic told me it has a chain. Interesting. I suspect it is because the Yaris is a world car (sold everywhere) and outside the first world an expensive disposable timing belt is a no go. Once again locost rules!


Top
 Profile  
Reply with quote  
PostPosted: July 15, 2018, 9:45 pm 
Offline

Joined: June 5, 2016, 7:03 am
Posts: 235
Location: ontario
vroom wrote:
I have an interference engine (Yaris) and when I took it in for a new timing belt my mechanic told me it has a chain. Interesting. I suspect it is because the Yaris is a world car (sold everywhere) and outside the first world an expensive disposable timing belt is a no go. Once again locost rules!


Interference valves can be found in any engine no matter which system is actuating valves, belt, chain, gear. It is a design choice. The issue is that when the system closing-opening the valves (in the interference type) fails valves end up colliding with the pistons. This is the problem. Years ago I had a 6 cylinder Volvo and the gear running valves self destroyed. The engine was not of the interference type and all I had to repair was the gear in question (about 2 hour labour and $150 part).


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 22 posts ]  Go to page Previous  1, 2

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 11 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
POWERED_BY