mark kibort

since ive heard that the euro 4.7 2 valver is an interference engine, why is it that ive not heard that you have to move the crank to 45degrees BDTC to keep the valves from hitting on a timing belt removal, as you do with the S4?

also, what euro 4.7 had the deep valve cuts? i originally thought the pre-84 did, but this engine being a 28.11 , (ie 84-86) (error, really pre 84 euro) it looks like it has the deep cuts. maybe due to the longer duration cams
(error. since those deep cuts are the pre 84 euro, the 84 euro with the flater piston tops have more compression due to the lesser valve reliefs.)

the pistons i cut valve reliefs on, modeled after the shallow cut valve cut euro pistons .(thought to be new 84-86 euro) worked well on my part euro 5 liter and early euro S cams. (pre 84).

Mk

Airflite40

I was told that euro engines were interface depending on how much carbon build up there is. My euro (80-83 K-jet) has relief cuts in the pistons as you can see below.

Airflite40

My engine is the m28-12, which is the auto version of the m28-11

mark kibort

THANKS!!! A picture is worth a 1000000 words! ive been wondering about this for some time. two things. first, my mistake, if its a 28,11 engine , its an 1983. (so not the 310hp 84-86 S version) Two, that the newer euro engine has the shallower cut valve reliefs. ( i had no choice, nor does anyone, when doing the valve cuts on a US 85 block to euro conversion. there is just not enough meat in the piston to do the cuts that deep) I was guessing before , and now I know!

Now, the question, is the only difference is the valve cut reliefs on the newer, more shallow euro S pistons to get that extra compression? if so how is this possible, unless the the goal was to increase compression with a sacrafice of interference, with a cam that has more lift and duration (well im only sure about the lift part!) either way, the difference of the valve cuts is dramatic. so, are the 84-85 euro S motors the only ones that are for sure interference types?

thanks guys,

MK

drnick

mark, the workshop manual has pics of the various pistons and those pictured above look like the M28.11/12 type with comp ratio of 10/1. the later euro engine is the M28.21/22 which has 10.4/1 compression ratio and smaller valve relief cutouts, this engine is the 310 bhp version.

mark kibort

so, since it seems that the 84 euroS with the smaller cut outs is definitely a interference engine, why does it not need special attention when doing a timing belt (the ole, 45 degree thing like the S4??)

the engine we are working with is is the 83ish euro S

mk

mark kibort

anyone... anyone??

drnick

the 84-86 euro is definitely an interference engine, i have the reciepts from a PO who had the camshaft break and bent most of the valves on that side.

mark kibort

so, if that is the case, why is there no 45 degree mark like the S4 to set the crank at when doing a timing belt. (a place where valves dont hit if the cams can snap the valves open accidentally)
I know this is a place so that you can rotate the engine crank with out valve interference if their is no belt attached.
in other words,
at TDC of the #1 cylinder , the movement of the cams is not enough to put a valve down far enough to hit based on the cam lobe lift or position? (where as in the S4, at TDC, the cams can move farther to create a hit)
Ive always wondered about this. seems like, espcially on the euro, where the cam specs are close to the same to the S4, you would think there would be the same issues.
anyone know?

mk

mark kibort

Does anyone know????

bcdavis

Search the archives...

This was debated endlessly at one point.

Someone eventually gave a solid answer on all the 928 engines.

As I remember, the 4.7 is non-interference, but if there was a lot of carbon build-up, it could be...

mark kibort

Now, i know the 4.7 euro 85 style is an interference engine, cause we (well rich) sucked valves when the cam broke (pre weaked by my accident)
i was only using 82 euro S cams, euro s valves and heads, but the more shallow 84-85 euro piston cuts.

i can only imagine that the 84-85 euro cam with greater lift would have more of an isssue. From the look at the 82 block on this thread, the earlier euro S engines look like they could be non interference with those DEEP piston cuts. i actually measured those and cc'ed them as well and it was a dramatic difference (something like 2cc for the 84 euro piston top vs 8cc for the 83 euro!!)

Still, my question is that if the engine is interference, wouldnt you have to follow the same procedures as the S4 for cam belt changing?? (ie locking flywheel at 45 degrees, etc) if not, why not.

thanks.

Mk

Micah Tatar

i have the 1981 euro s 5 speed and broke timing belt and replaced fine no damage if that helps

drnick

mark, its an interesting point - why isnt there the instruction to lock off the flywheel at 45 degrees? however there seems little doubt that the 84-86 euro is an interference engine, would be interesting to know about the earlier ones also.

Vilhuer

45 degrees might be afterthought when they realised doing adjustment at 0 degrees was riskier. Obviously belt swap can be done at any spot of 360 degrees as long as crank and cams do not move while belt is off.