AZ455

Does anybody know for sure if the 455 is an interference engine or not? Didn't come across this on the forum anywhere... Thanks.

joe_padavano

It is not, assuming stock valve lift and stock pistons.

AZ455

Thank you. Good to know.

rustyroger

Interference engine? - is this an Americanism I don't understand?.
What do you mean by interference engine, the more I learn the more I realise I don't know, help me plug this gap please.

AZ455

In an interference engine if a timing belt or chain breaks, the pistons and valves can collide causing damage to both. Their paths "interfere" with each other if the timing is not correct.

ah64pilot

Its a Japanism...most foreign cars have interference engines. American engines don't typically have such close tolerances. That's why your Honda timing belt gets changed at 100,000 miles.

coltsneckbob

That implies that such an engine is fairly high compression. Frankly though I don't see how any engine is not an "interference" type. Even if the cam(s) and crank are gear driven such a scenario is possible.

rustyroger

Thanks guys, I guess the term isn't used much here because just about every engine in modern cars over here is an interference engine.
Roger.

MDchanic

If the 455 is NOT, then is the 350?

I ask because in my personal experience, the 350 IS.

20 years ago, I had a stock 1970 high-compression 350 slip a tooth at idle, and it bent 4 valves.

- Eric

Project Grandpa

I specifically remember a 70 442 in an old shop I worked for in the late 80s that snapped a timing chain and literally bent every pushrod in it. And it was abone stock driver.

joe_padavano

Well, I did the same on a 1970 350 motor, and it did not hurt the valves at all.

Project Grandpa

To give levity to the original topic, I had a 2002 Mazda 626 with a 4 holer towed into my shop today. Broken timing belt. The engine IS a valve bender, but I gave it a shot anyway. Pulled the valve cover off and noticed no gaps between the cams andthe followers. So I threw a new water pump and timing belt on it then set the valve cover back on. Sure enough it fired right up. On most Crapanese engine bent valves will leave a gap under the cams giving up the answer right away. This customer had originally called for an estimate on getting the head done as he was at Tire Kingdome of all places looking at a $1800 repair.

I got him out for $450.50 with tax.

Point? Some do when they aint supposed to and some don't when they are supposed to.

Andy

MDchanic

Weird.

I took it apart (in a parking lot, 5 miles from where I was staying, away from home, with no car, since that WAS my car), confirmed that the chain had in fact slipped, replaced the chain and gears, tried to start it, no luck, odd cranking sound, seemed to wing over a little too easily, pulled the heads, four (at least) valves (I remember at least 2 on each side) were sticking open, when viewed from the combustion chamber, did not respond to some "persuasion," so I said "screw it." I was in no position to drag the heads to a machine shop on a city bus, and had no money anyway.

The findings were NOT subtle, though.

My life would have been much better at that time if I had had YOUR engine .

- Eric

AZ455

Is this more common on the high-compression engines?

Run to Rund

Olds valves are 6 degrees off "flat" whereas some like small block Chevy were 18 deg. Olds pistons aren't domed. Therefore there is generally plenty of valve to piston clearance even with very big, high lift camshafts (you can run into trouble with tight deck clearance, domed pistons, etc.). However, if the valves are held open anywhere near full or half lift and the piston gets to TDC, you will have interference. There is no way to avoid it with virtually any modern engine, but the Olds isn't nearly as "bad" as most.

scubastever

any Mazda engine with a timing belt, is non interference...
the timing chain engines are interference.

Tony72Cutlass'S'

Eric or Joe,

I was just posting on another thread (new carb won't start 350 cutlass), and we suspect that my timing chain has jumped.

I have a 72 Stock 2bbl 350 Rocket, can you guys confirm if it's inteference or not. I'm REALLY worried.....

Also, timing chain set (Cloyes C3006K) is in the mail with the gasket set Eric suggested.

Is this something i can do in my garage? Eric, you say you removed the timing chain on the road, you're a pro, other than a balancer puller, what do i need??

MDchanic

It shouldn't be able to have hit the valves.
Also, the low-compression motors have more clearance because of the deeper piston dish, so I wouldn't worry.

Sure, as long as you've got some room at the front of the car.
The coolant has to be drained and the fan and the fan shroud have to come off (if you like a lot of space to work you could pull the radiator as well, since you're draining it anyway), then you remove belts and pulleys, water pump, and pull balancer, then remove timing cover, cam bolt, gears and chain.
You MAY need a gear puller to get the gear off the crank.
You may find it helpful to loosen a bunch of oil pan bolts to be able to lower the front of the pan a fraction of an inch.
You MUST loosen the fan nuts BEFORE you remove the belts, or you'll go insane trying to somehow get a grip on the fan pulley and turn the nuts.

HA! I'm no pro - just a scrounge!

I'd have a gear puller for the small crankshaft gear, just in case, also a gasket scraper, since the timing cover will be a mess.
You'll need something to loosen (and re-torque) the crank bolt - an air wrench is the best to remove it, but a long breaker bar resting on the ground on the driver's side of the engine will serve the same purpose - give a toot or two on the starter and the bolt will loosen.
I'd recommend a torque wrench for reassembly, as the torque spec is "160 minimum."
Also, some engine paint in the correct colors, as you Might As Well clean and paint all those parts while they're off...

Good luck!

- Eric

rustyroger

I remember back in the '80s some UK spec Ford escorts were supposed to have interference (thanks for enlightening me) engines but if the belt failed when trying to start the engine then normally they got away with it. This was a fairly common problem with neglected maintenance.

Last week I checked out a diesel Vauxhall Cavalier (Completely different to the Chevy Cavalier) which had a belt failure.
The camshaft was broken in 4 places and one of the retaining caps was smashed, #3 connecting rod was bent and the big end bearing squashed, the inlet valve on #3 had bent and damaged the valve seat and the piston crown was damaged. It's not unknown for these engines to break the crankshaft if the belt fails at high speed.

I always replace belts with either a genuine makers part or use a Gates item, I also always replace the guide pulleys at the same time.
Never had one fail me yet.

Roger.

Tony72Cutlass'S'

Hi Roger,

I dont think there are any tensioners in our oldsmobile engines for the timing chain (the 1972 version anyway) From what it looks it has a standard number of teeth on both gears.

I've also got a 1994 nissan sentra, it's been mine it's whole life. I've only used Mobil 1 synthetic oil so i'm hoping the engine will last well into the 300 large mark.

rustyroger

Chain tensioners were fitted to most UK spec pushrod engines up to the '80s, the chains were prone to stretching because the technology wasn't there to make good ones at a low price, some didn't, the BMC A series as used in the original Mini and Morris Minor is an example. Timing chain noise as the engines put on miles was accepted as normal.

Belts became popular as engine design switched to OHC, replacing a belt is a lot easier than a chain (a horrible job on XJ Jaguars!) and it cost less to make such a system which pleased the bean counters at the factories.
Replacing the belt was accepted as necessary maintenance by most owners, and its main advantage over chains was the timing stayed correct, as a chain wore it had the effect of slightly retarding valve timing.

Chains are becoming the norm again as they are better made nowadays and now most small cars now have a power steering pump and often an A/C pump squeezed into overcrowded engine bays making belt replacement a more difficult task. To replace the belt on my fiances diesel Peugeot involves removing an engine mount and hard to get to covers, it takes me about 3 hours to do the job and I've had plenty of practice at changing belts.

An old girlfriend from Dallas has an '87 Sentra, when I met her her car wasn't well maintained but I serviced it for her and one of the first jobs was replacing the timing belt. It was a very easy job - well within the scope of a shade tree mechanic - and the car had 200+k miles under its belt with more to go until she parked it in a tree. It struck me as a tough little car that kept going despite neglected maintenance, if you look after yours I think you should get your target 300k from it. It probably wont be trouble free but repairs are cheap and easy and shouldn't be too frequent.

Roger.

Tony72Cutlass'S'

Great Info!

I always heard my professors in school talk about the Old mini's, they all went to the university in Keele. Supposedly those engines were built like tanks and had cast iron pistons!

It's interesting you say that the 87' sentra had a timing belt because my 1994 has a timing chain? I wonder if they changed the design when they reached the 90's.

Over the past weekend i replaced all balljoints and struts in my sentra, what a job! I'd prefer working on my olds!

rustyroger

The A series engine was designed around a number of Harry Weslake patents in the early 50s. He was a respected engineer in his time.
His design incorporated a heart shaped combustion chamber in the cylinder head and siamesed ports and bores.
This design gave great fuel economy at low build cost but had drawbacks such as poor gas flow.
It was a long stroke engine on 3 main bearings that in its original 803cc form put out 32 tarmac rippling bhp!
It rapidly gained a reputation for being very tunable mainly because doing almost anything sensible to it would see a power increase.
In its most powerful factory form as a turbocharged 1275cc unit it was very lively but very prone to head gasket failure.
In the '70s someone built a drag car with an A series engine he managed to get around 180 bhp from somehow.

I don't think they ever had iron pistons, but early engines had split skirt ones.

They were tough engines that would keep soldiering on with knocking big ends and broken rings long after other contempary engines would have given up.
They were prone to head gasket failure as the siamesed bore design left little room between them for a gasket to fit, and 200 miles per pint of oil was normal partly from ring wear and partly because they often leaked badly.
Main bearing wear was another problem but they would keep running on very little oil pressure.

However the engine was made from 1952 through 1990 in various displacements and British mechanics were very familiar with them, it was a very basic ohv design and very simple to fix. Getting one out of a Mini was an all day job though because the gearbox was effectively the oil pan requiring the whole assembly to be lifted out of the car and a special puller was needed to remove the flywheel.

I agree, I'd rather work on my Olds!.

Roger.

Tony72Cutlass'S'

Can't believe 10 years has passed since we had this conversation!

The timing chain replacement went great, but i'm thinking i'd like to get a little bit more power out of my 350. I've been looking around at pistons (like the new forged flat top ones that i believe Mark sells) in the hopes that i will be able to pull my engine out for a freshen up.

Is there a worry about putting flat top pistons in my 350 (right now i have an original dished set) about smacking my valves?

67OAI

Depends upon how radical a camshaft you would use. Most street or street/strip grinds would not present a problem with flat top pistons. If you are using Mark's Mahle pistons, they have pretty deep valve reliefs; the forged SpeedPro pistons have no valve relief, they are basically the W31 piston but forged.

Tony72Cutlass'S'

ive been actually planning to give mark a call to discuss! I don’t want to do anything too crazy camshaft wise.

I’ve always had the original 2bbl camshaft in there, so I really have nothing else to compare it so since I’ve only ever owned this one sports car.

Originally I planned on reusing whatever I could, but since I’ll be sending the block, crank out to get machined after I take it apart, I figure now is a good time to make any other tweaks.

can’t believe she’s turning 50 in November this year, I should throw a birthday party!

MDchanic

Alright, since you invoked me, I'll answer, though I won't claim to be saying anything earth shattering, and I'll qualify what I say with the fact that while I have assembled engines using the parts that they are (more or less) "supposed" to have, I have not spec'ed and created a new engine from scratch.

The question of valves hitting pistons is all a matter of measurements and arithmetic.
You use crankshaft throw length, con-rod length, compression height, and dish or valve-pocket depth to determine where the piston will sit, then you use camshaft lift, rocker arm ratio, and valve guide angle (assuming that the piston's plane of oscillation is zero degrees, your valves are moving at some specific angle to that, depending on engine design), with valve diameter, to determine where the closest part of the valve will be when fully open.
Then, having ordered the parts based on your calculations and assembled them, you put it all together, and use a piece of clay to determine the actual clearance before rotating the engine through.

Varying valve diameter, valve lift, valve timing/duration, rocker arm ratio, pushrod length, piston dish / crown, compression height, con-rod length, or crankshaft, outside of what the original engineers decided on, or what later builders have successfully used, can always potentially lead to trouble, even in non-racing applications (the "classic" low-compression Subaru engine will bend valves if the timing belt breaks or is improperly installed), so one should always do the math before finalizing a plan, and then test "IRL," or else follow someone else's successful "recipe" to the letter (and then still test).

Good luck!

- Eric

Tony72Cutlass'S'

Awesome thanks for the reply! I have the service manual kicking around so I will start to dig up all the numbers and see what I can come up with. When I first got the car the old plastic timing gear skipped and nothing happened (luckily), which makes me like having some buffer.

I’ve been thinking of going down this road since I’d like to pull the heads to fix an exhaust leak (previous owner snapped two manifold bolts thinking he would put headers on the car ).

Then I’ve been reading that new head gaskets are thicker than the originals, so I don’t want to be further behind if I add volume to my combustion chamber by using a thicker head gasket. If you were to freshen up your motor would you stick with the original style of pistons with fresh rings, or will that not make much of a difference?

Thanks again!

Tony

MDchanic

Welllll... What I did do was to have my heads shaved to account for the increased thickness of modern head gaskets, then I measured the volume of my pistons at TDC and of my combustion chambers, and slightly ported the heads and ground the combustion chambers to make them all equal in volume.
But that was with high compression pistons, where I didn't want to lose compression, but I didn't want it to go too high either, especially in only one cylinder.
That engine had minimal cylinder ridges and still-visible crosshatching, so I did not mess with the rings.

Oops, that reminds me: I missed a dimension in my last post: Head height, specifically, the height of the bottom of the valve seat above the head sealing surface.
It varies. These heads were not super-precision cast. Also, if you shave the heads, you can bring the valves closer to the pistons (depending on the dimensions of the new and the old head gaskets).

- Eric

Fun71

Won't the interference thing only be an issue if the camshaft loses its correlation to the crankshaft? As in it would be an issue only in a situation such as a timing chain failure?

matt69olds

I know for a fact if cam timing is off enough, valves will bend. I have torn down plenty of core 455s with bent valves and wasted timing chains to make that fairly obvious.

A friend of mine built a 455 with the speed pro L2323F pistons, He had a pretty hairy aftermarket cam, and timing chain set with multiple key ways. I guess he didn’t read the directions, or didn’t follow the directions, but he installed the timing chain way off. Several bent exhaust valves was the result.

Replaced valves, installed the chain correctly, all was good.

My sister had a 80 Olds cutlass with the mighty 260 engine. The car was gutless even by 260 standards, idled rough, just really lazy. One day it wouldn’t start, the chain had jumped. Replaced the chain, cleaned out the oil pump pickup, the car ran much better.

Im betting the piston design and cam profile is a determining factor. Low compression pistons with a girlie man camshaft, I bet the engine will live with a jumped chain.

Tony72Cutlass'S'

I'm hoping i never have that problem since i've been using a good timing chain for the last 10 years or so with no skips.



I'm pretty excited to get this engine apart and post it in my old build thread. If i manage to get the engine out, would you guys run any checks like looking at piston to bore clearance or crankshaft journal to main bearing clearance to assess the health of the motor? Maybe if everything looks good i can just get away with a new head gasket and camshaft to lighten things up.

olds 307 and 403

The Mahle pistons have 10cc valve reliefs. Even with Speedpro flat top pistons, you need an extremely aggressive cam, 0 deck and less than .040" piston to head to be an issue. Good luck on the rebuild.

Tony72Cutlass'S'

Those look really slick, did you reuse your stock connecting rods?

olds 307 and 403

No, I got these from Mark as well. Stock rods can be used as well.

Tony72Cutlass'S'

very cool thanks!