Great work Tom - keep it up. I would love to see it in action.

mk3 gti sidedraught head, cost me £10, but as you can see it has suffered from timing belt faliure although it wasn't casatrophic, possibly broke on start up... you can see the piston to valve contact on the number 1+2 exhaust valves (on the right in this pic)...

i've also noticed that the stud for the timing belt tensioner is M10, and on the mk4 crossflow head it's M8.. i can't use the mk3 tensioner because the mk4 belt is wider, and i can't use the mk3 belt because it's longer, so i need to figure out some way of putting an M8 stud in an ole' that had an M10 one in there, i might weld up the hole then re-drill and tap the hole...

from initial inspection, it appears that there are only 2 bent valves, but when i get a chance i'll strip it down and check it all properly

Can you helicoil the M10 thread down to M8, or sleeve out the M8 hole to M10, or find a belt from a 3rd model which is the correct length and width (tooth spacing is standard)?

Also, if the head's had a belt failure, check the cam bearings are all ok and line up properly (DAMHIKT!!).

the cam still turns ken. so there is no misalignment there. also, a can't do that with a helicoil or an insert because the thread pitch is different (1.25mm on an M8, and 1.5mm on an M10)

So why not cut the smaller hole to the larger one and just use the larger stud?

So why not cut the smaller hole to the larger one and just use the larger stud?

He needs to use the M8 stud, the hole is already M10 so to big.

He needs to use the M8 stud, the hole is already M10 so to big.

That makes 2 of us which that wasn't obvious to.

He needs to use the M8 stud, the hole is already M10 so to big.

So couldn't you take the stud out of the M8 device, make that hole M10 and then put an M10 stud in there?

I'm probably missing something obvious.

The stud is wound into the head. the tensioner then slides over the stud and a nut goes on the end. You cant change the dimension of the hole in the centre of the tensioner.

ok to use the helicoils you need a helicoil tapped hole would you be able to run an M10 heli tap through the M10 hole in the block, then put an M10 to M8 helicoil in?????

i'd have to look at a helicoil spec sheet to check if the pitches would work out.

Just turn it down... and cut a new thread on the end

Just turn it down... and cut a new thread on the end

:rofl:

Keeping in mind that this stud is fairly critical to the engines survival...lol

I reckon you should fill the hole with weld and then drill/tap.

ok, i'll answer back to some of the suggestions raised...

it's not possible to re-drill the tensioner because he centre part is hardened, the drill would just break,

although it 'might' be possible to turn down the stud, it would be an absolute pig getting it to run true, the stud needs to spot on perpendicular to the head otherwise the belt will jump off...

one option i'm looking at is putting an insert inside another insert, either that or use a thick walled insert, put i need to go and visit the boys at german and swedish in portsmouth, there's a guy there who knows the 8v units inside out, and there might be an alternative tensioner i can use with an M10 hole in. from a 16v??

if you keep the 10mm threaded portion on one end, and turn the shank down to 8mm and

thread that on the end? Or have I missed something?

if you keep the 10mm threaded portion on one end, and turn the shank down to 8mm and

thread that on the end? Or have I missed something?

Thats fine, its just getting it spot on thats difficult.

Thats fine, its just getting it spot on thats difficult.

:iagree: and how am i going to clamp it in the chuck without chewing the thread off:)

Thats fine, its just getting it spot on thats difficult.

Why? Are we not engineers? :confused:

i've been doing a bit of digging about, and it appears i may be able to use the tensioner from a 16v ABF engine, the timing belt is the same width as the the mk4 belt, and it goes over an M10 stud... i'll go and have a look at one in the morning

I'm really confused now. Exactly how can you run a stud into the block through the centre of a tensioner wheel?

I can see how you could do it through an idler wheel, but a tensioner I'd expect the axle of to move relative to the cam and crank axes.

there's a stud about 50mm long srewed into the cylinder head, the tensioner has a hole in the centre(eccentric to one side slightly), the tensioner locates over the stud, washer and nut to secure it in place:confused: as Mr Ross said above

turning the tensioner around it's eccentric axis alters the lateral position of the tensioner and hence tensions the belt

Ah, it makes sense now. I'm used to tensioners being like swinging alternators, only rather smaller.

the boys at german and swedish did good... timing belt tensioner from vw IDI diesel engine, with 10mm hole, the offset is slightly different so i need to make a spacer/washer to go behind it

mk3 sidedraught cylinder head stripped, checked, de-coked, skimmed and cleaned ready for lapping in valves