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| return of the old interference engine trick https://slantsix.org/forum/viewtopic.php?t=55866 |
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| Author: | bob fisher [ Sun Jul 27, 2014 10:45 am ] |
| Post subject: | return of the old interference engine trick |
hi sages- was looking at a slantsix vehicle shop manual and it had a diagram/picture of the cylinder and head design cut away and viewed from the perspective of the front of the engine. it shows the piston at its maximum height in the cylinder with the valves at the upper hypotenuse of the wedge head. didnt know sl6 was a wedge head. told more than once no sl6 was ever an interference engine, but it appears from this picture that should the timing chain bust or skip out of time , a valve or valves could stay stuck open , crash into the pistons and toast the engine.uncle moe says this could happen on an overhead cam engine witha busted chain or belt but not on an ohv engine . my thought is that the actual piston to valve clearance even at tdc allows enough clearance to prevent damage in the sl6 regardless of the way the picture looks. who is correct me or moe? thanks tons bf |
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| Author: | Rick Covalt [ Sun Jul 27, 2014 10:52 am ] |
| Post subject: | |
It depends on your build. On a stock slant with .150-.180 deck height there may not be any interference at all. On a long rod engine with a high lift cam it is a different story. If the timing chain broke or for some other reason the valves get out of time they can and will hit the pistons, When my engine exploded last year it had 4 valves that hit the pistons after the cam gear bolt got sheared off. Mine was a 225 with a -.025 deck height. Rick |
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| Author: | Charrlie_S [ Mon Jul 28, 2014 3:44 am ] |
| Post subject: | |
I have never actually checked, but I think a STOCK 198 or 225, would not be an interference engine. A 170, however could be a different story, since the piston comes up to the top of the block. |
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| Author: | lgu32 [ Mon Jul 28, 2014 5:57 am ] |
| Post subject: | |
I have got exhaust valve hits to 225 piston with both Mopar performance 244 degree as well 268 degree cam. I have had oversize valves. With more radical cam both head and block were milled (for 10:1 cr). With 244 cam the engine were "blueprinted". Strong valve springs solve the problem... |
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| Author: | bob fisher [ Mon Jul 28, 2014 11:38 am ] |
| Post subject: | the stock 170? |
hi charlie s , igu and rich- curious answers. have had many sl6s since 64. have had a few broken or jumped timing chains, but never a wrecked engine due to interference. most were 225s and all were stock. never had a 198. no hot cams either, just stock. so it seems all stock 198s and 225s are non interference. had to put a new chain and its gears in a 170 many years ago, but it had no piston/valve damage. never heard from other mechanics or diyers that there was any busted pistons or valves in these engines if stock. 2 questions anybody here have a stock 170 wrecked in this manner? also, how would strong valve springs avoid this problem? if the valve is open when the piston comes to the top of the block and there is not enough clearance, they will collide right? thanks tons bob f ps- same experience with 273s and 318s. however was told that the 383 was an interference engine. |
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| Author: | Charrlie_S [ Mon Jul 28, 2014 2:15 pm ] |
| Post subject: | |
Just checked a 170. It is an interference engine. The valves will hit the piston, at full lift at TDC. |
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| Author: | bob fisher [ Tue Jul 29, 2014 6:29 am ] |
| Post subject: | wow interference 170 |
hi charlie s- thanks for the info on he 170. very surprised that i never heard a word about stock 170s being interference. have been a member of this forum for a long time. 170s were made from 60 to 69. there were a lot of them out there b/c they were the basic engine in the a bodies. in 70 it was replaced by the 198. apparently that and the 225 were all non interference. one might think there would be an artcle or complaint history about that engine (170) self destructing when the chain wore out or malfunctioned. have heard lots of these complaints with other makers interference engines. now its hard to find a manufacturer who offers a non interference engine. apparenty this anomaly was put in cars to obtain more power, higher mpg and lower emissions out of smaller engines . the fallacy of course is the repair bill for an engine wrecked by a busted belt or chain will wipe out any mpg saving. almost seems like a scam to enhance profit margins for dealer repair shops. interested in your thoughts , fellow sages. thanks tons bob f |
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| Author: | mpgFanatic [ Wed Jul 30, 2014 8:13 pm ] |
| Post subject: | Re: wow interference 170 |
Quote: now its hard to find a manufacturer who offers a non interference engine.
Isn't that largely because the timing belt has been the status quo for at least 25 years? Timing chains are a rare and welcome relief, for all of us who appreciate longevity in our machines.- Erik |
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| Author: | bob fisher [ Thu Jul 31, 2014 12:03 pm ] |
| Post subject: | belts, chains etc. |
actually i dont think whether the engine has a timing belt or a chain has anything to do with an interference engine. i think the only reasons for the belt are 1. it is cheaper than a chain and 2. the belt which you are typically advised to replace at 60k miles creates a $400 job for the dealer.never saw an instruction for a timing chain engine which said replace at 60k. every chain engine i had, the chain lasted over 100k. i have a mercury marquis with a standard 4.6 v8 and a saturn L100. both are interference , both are 2001 and both have timing chains. volvo 240 has a timing belt and is non interference. watch your wallets. regards bob f |
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| Author: | WagonsRcool [ Fri Aug 01, 2014 10:58 am ] |
| Post subject: | |
Over the past ten years or so, I,ve been seeing more new cars that use timing chains instead of belts. Could be that a chain should have a longer service life, is somewhat more compact, fewer oil leak points, lower maintenance/ warr. costs, etc. Interference designs are mostly the norm for decades- chain or belt. As emissions & mpg regs have tightened, compression ratios have gone up & designers have had to get rid of big valve reliefs in the pistons & other "open" spaces in the combustion chamber to reduce HC/CO. |
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| Author: | bob fisher [ Sat Aug 02, 2014 6:01 am ] |
| Post subject: | interference and emissions |
hi wagons r- good to hear from a colleague from nj . had my best car there a 77 aspen wagon with sl6 and 4 speed od. despite multiple weldings it turned into a rust flake. chains are much more reliable and longer lived than belts. but even if a chain busts in an interference model, engine will become scrap metal. seems emissions conundrum has dictated the interference anomaly. ps- been in fla now for 10 years. still looking for a 4 dr or wagon f body with a 6 and 3 pedals on the floor. none in fla and appear to have disappeared in jersey too- maybe you have one one to sell me? phat regards, bob f |
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