Can anyone tell me the standard 383 cam timing figures?

[Rog's troubleshooter]

In my other thread that's running ("which vacuum port...." ) I said that I felt the cam might be timed incorrectly, as the engine is so "flat", but I can't track down the cam timing figures to check.
I did a "quick and dirty" check this afternoon, looking for the valve "rock" point -ie Ex valve just closing, In valve just opening- on #1l (and repeated on#3R), by removing the rocker covers and inching the engine on the starter. This showed that there was no apparent valve overlap, and that the rock point was somewhere between 12 and 25 deg After TDC. This seems very late to my experience with other engines, where I'd expect that point to be TDC at the latest, and the In valve opening at between 25 deg BTDC and TDC.
You can see in the attached pics how far the timing is after TDC - the timing marks are highlighted in white.
Can anyone enlighten me as to whether this is typical of the 383 cam in the Jensen, or tell me what the nominal figures are for the cam?
thanks in "advance" ,
John

[taximan]

Replaced mine with this cam, the figures given must be close to the "norm" for a 383.

http://www.jegs.com/i/Edelbrock/350/2192/10002/-1" onclick="window.open(this.href);return false;

NB: this is for a 68 or later engine. Your profile doesn't give us the car your 383 is fitted in.

Checked your newbie post and found ref to a MK2.

Shaun.

[Rog's troubleshooter]

HI Shaun,
thanks a lot for that info - it's looking more & more as if the timing gears have been assembled 1 tooth out (or the engine has the ally/nylon gear which is breaking up and has let the chain jump a tooth)
I think the camwheel has 38 teeth, which is approx 9.5 deg per tooth, so that would be about 19 deg "late" on the crankshaft.

Did you change your cam with the engine in place?

thanks for the help,

John

[taximan]

Yes engine in car and thick towels and carpet over the wings, remove carb inlet manifold and valley pan, alternator, water pump, front pulley needs a puller and timing cover, set of gaskets, timing chain set and the camshaft kit inc lifters cost about £450 at a guess. Also radiator needs to come out because the shaft comes out the front.
Shaun.

[Rog's troubleshooter]

Thanks for that, Shaun - I 've now got the info that the engine has been rebuilt, and checking via the distributor opening there is a steel cam wheel and the chain looks new, so I'm actually hoping it may just be a case of re-doing the timing chain fit work.
I might take off the inlet manifold/valley cover and have a look at the cam, though.
On the back burner now for a week or so, though.

Incidentally, I discovered a worrying warning (for me) on the instructions supplied with your Edelbrock cam.....

CAUTION: Use Edelbrock Performer-Plus Timing Chain
and Steel Gear Set #7804. Do not use late model timing chain
and gear sets that are designed for emission-controlled
engines. These timing sets are machined in a retarded position
and are not recommended for this camshaft installation.

I wonder if that's my problem?

Cheers for now,
John

[Rog's troubleshooter]

Rats - just found this post from "Martin R" on another thread......

Looking at the timing gear through the dizzy hole can be misleading - Dino said; "if you can identify whether the gear has been replaced at some point and does not have plastic teeth, that may be a start".

However, if it's a truly knackered gear, it can look like my old one below, with NO PLASTIC remaining!

The gear I could see had the big holes, so I'm now wondering if it's an ally one with all the nylon gone!

John

[taximan]

Whip the sump off and check for loads of black bits of plastic in the pickup strainer.(2 bolts at front go into bottom of timing cover)
Shaun.

[Dion]

My car still had bits of nylon remaining on the gear wheel. The oil pickup was full of little parts of nylon.

IMGP1535.JPG (107.53 KiB) Viewed 5045 times

nylon tandwielresten.jpg (82.28 KiB) Viewed 5045 times

[Rog's troubleshooter]

I might take the valley cover off first, as that'll let me check the cam too.......

Thanks for all the help & suggestions - updates when I get back onto the engine in a week or so.

Cheers,

John

[451Mopar]

It sounds like it is a tooth off, but FWIW, I think from around 1967 to 1971 the Chrysler 383 only had two cam choices. The Standard cam and the HP cam. I am not sure which would be in the Jensen 383?
I think the standard cam was used in the 2-bbl engine and has specs of 260/268 duration, 0.425"/0.435" lift, 113 LSA installed at 112 intake centerline.
The HP cam is 268/284 duration, 0.450"/0.458" lift, 115 LSA, installed at 113 intake centerline. The Mopar Performance cam P4452783 is the same specifications.

[Rog's troubleshooter]

Well, I've quit!
I didn't get as far as taking anything apart, as while we were trying the car with the vacuum pipe disconnected and plugged ( see my other thread " Which vacuum port etc") the engine suddenly run very roughly and we only just made it back to it's garage.
It now refuses to start. Point blank refuses. It has an excellent spark at the plugs, the timing is OK and it has fuel. It just won't start. Even with Quickstart. Not even a cough!
When I redid my rough & ready cam timing check, I couldn't even see the timing mark - it was too advanced.

I'm feeling it's now skipped another tooth........ (or something more dire) .

It goes in for specialist attention next week, so if I learn anything interesting, I'll update the thread.

Cheers, John

[451Mopar]

I just bought a nice digital camera that I can take videos with, and I plan to video document several of my car projects including the Jensen.
I am planing to start with checking the cranking compression pressure, leak-down test, and measuring timing chain slack on the Jensen just so I know what I am starting with.
If I remember to do it, I will measure the stock camshaft specifications before rebuilding the engine.
I still have not decided on the engine build? I have some Brodix B1 B/S heads (65cc chambers) that with the stock low compression pistons should get the compression ratio up to about 9:1.

My compression calculations for the stock engine are showing about 8:1.