1.7 J Head Exhaust Valve Upgrade to 34mm

Green626 · Post by **Green626** » Sat Aug 26, 2023 10:17 am

Happy Saturday
this is my forst time posting on the board : but I have been lurking for a while
I have a technical question -
I am having my 1.7 j heads rebuild for a refresh of my original engine - all 4 of the exhaust valves needed to be replace - I decided to move up to a 34mm valve - based on that it will need new seats - I want to make sure I purchase the correct ones - i there are various sites that carry replacement seats - sizes start at 32mm, 35.5mm, 37.5mm ... there is no info on if this is ID or OD for the seat - before I make an assumption I want to see see if any one has done this and what is right.
Maybe I am over thinking it but my gut is I need the 35.5 if that is the OD

Nick

Post by **AdminSteve** » Mon Aug 28, 2023 7:38 am

Most of the sites list them based on the valve size you are using not the OD so a valve seat listed as a 35.5 would be for a valve that is 35.5 in diameter.

AdminSteve

Green626 · Post by **Green626** » Mon Aug 28, 2023 8:28 am

Thank you for that insight that is helpful - Any idea where I can get the replacement seat for a stock 34mm exhaust valve ?

Post by **Piledriver** » Sun Sep 03, 2023 11:16 pm

Go 36mm, its a standard size used on the 2L 914, fairly common.
Si makes good valves.

If you are feeling adventurous, Mahle et. al. make sintered/PM seats infused with copper these days, hard as stellite, cools like BeCu seats.
Its the machining that costs the $$$ the better seats wont cost significantly more, most OEs use them these days.

Worth asking your machinist about.
Also...Anyone who does heads should have multiple sources for seats.
If they don't regularly "do" Aircooled VW heads go somewhere that does.

Green626 · Post by **Green626** » Mon Sep 04, 2023 7:22 am

Thanks, this is helpful, I have original dome top pistons that I have that I plan to reuse any recommendations on piston rings? I am really going for a refresh on the top end.

Post by **Piledriver** » Mon Sep 04, 2023 9:13 am

Replacement 90mm piston ring sets are available from many sources if you are certain of the existing bores being dead straight.
...CB Performance, PMB performance, Pelican parts, Automobile Atlanta (all excellent 914 parts sources) Jegs probably even sells them.
You could actually go with a modern ring set with ring shims, but the bores have to be dead straight.

Otherwise have the heads cut and go 96mm, you'll end up with the same or slightly higher compression and a ~250cc bigger engine.
(this is both "the easy button" and best solution)

I'm currently considering sticking some 100mm Mahle birals into 1700 heads in an unconventional way... Step cut for an additional 6mm of deck thickness, with a 2L crank and AA h-beams for use boosted.

Green626 · Post by **Green626** » Tue Sep 05, 2023 7:57 am

If I go with 96mm pistons and cylinders how will that work with the stock DJet 1.7 Fi? Can it support with out major adjustments

Post by **Piledriver** » Tue Sep 05, 2023 6:32 pm

DJet---That does throw a wrench in things.

I have been using Megasquirt so long I forget some folks cannot convert to a stand-alone ecu...
The DJet manifolds, fuel system etc all work great with stand-alones, although the TPS needs swapped out its very easy.
(you can also convert to new, modern injectors you can actually buy)

I have heard retuning for 1911cc is quite possible (have not done it on Djet myself) but aside from adjusting the fuel pressure no other adjustments are really trivial... although a slight bump in fuel pressure is mostly all you need for a slightly larger engine, you are mostly stuck with a stock cam profile or a web 73 at most due to the way DJet works. The pressure sensor may need slight adjustments for best tip in...

It's hard enough to adjust Djet sometimes to work properly for a bone stock engine.
I successfully managed to get djet working for people but that was ages ago when you could still get new parts.

Ray Greenwood is a master of DJet, I would ask him.
He also may have a source for new domed pistons and better ex valve seat material.

The biggest concern with reusing worn pistons is not simple skirt wear--- there are reasonable solutions for that.
The ring grooves wear and lose their sealing ability... possible to fix (cut larger, use filler spacer rings) but custom pistons likely ~same price.
Your existing jugs are very likely not reusable, so you are looking at a new set of cylinders in any case.

raygreenwood · Post by **raygreenwood** » Wed Sep 06, 2023 7:55 pm

thanks for asking Piledriver!

OK. First as you have been advised, going from a 33mm valve to a 34mm valve there is not much economy in that simply because the choices are narrow.

Before we get deep into the heads, you are keeping this a stock 1.7L right? What are you using for a cam? If its time for new valves and seats its WAY past time for a new cam. The stock cam ran ok but ran hot by design and type 4 cams wear out. Post a picture of the lobes and we can tell you. But if its not totally worn out yet....it will be in another 30-50k miles. Why put a mostly worn out cam back in a refurbed engine with new heads?

So, there are a few choices out there of what runs good with D-jet. all of them will also need slight tuning of the MPS.
Your only other option is to find someone who can and will regrind your stock cam...and reharden it...and find lifters that are matched to it...which is a real crap shoot...50/50 unless you buy tool steel lifters from Europe. Pricey but they should be fine with any cam.

So, the heads. They were 39mm by 33mm diameter valve heads. Yes you can go 42 x 36 and manley makes a good set just for the 914. SI makes nice valves. The valves that Pelican sells are AE brand....Federal Mogul. I have no info on those yet.

There are a couple more options. I have a set of 42 x 36 valves made by Intervalve in Switzerland. I bought them about 10 years ago from Pelican. They are very nice and the reviews at the time from the 914 guys say they are pretty good certainly good enough for street use..

They have hard chrome stems and hardened/stellite tips. That should be the prerequisite for ANY valve you buy. Intervalve if you look them up on line has a 800+ page catalog. https://www.intervalves-technologies.co ... s-2022.pdf
On page 425 they show both the 42 x 36 for the 2.0L and the 39.2 by 33 for the 1.7L.

They also have them in 34mm exhaust and 41mm intake for the 1.7 and 1.8L. I do not know who are intervalve dealers on this continent at the moment.

As for guides....do not buy them yet. Get your heads to someone who works on type 4 or Porsche 914. Get the valves to them. In this modern times you should go ahead and go to 8mm valve stems on both intake and exhaust. The valves now are way better than back then.

Seats should be at a 0.006" interference fit...no more. SI can and will make you ANY size valve guide you need for cheap if they do not have it in stock. Type 4 and 914 valve guides are tough to do right. Too much interference fit and they will be loose. Too little and they will e loose. They have to be installed at a very narrow temperature range....that is straight from Len Hoffmans mouth to me.

So whoever does your heads, they do seats first. Then guides and then cut seats for valves. Some of the nicest seats I have ever seen and they really are not that pricey is CHE precision
https://www.cheprecision.com/part/seats/

So the person doing your heads will be able to tell when teh guides come out...by measuring....how much oversize you need on the OD and how much size you need on the iD. Then SI can make you exactly that and probably have them in stock.

The seats from CHE are a blended bronze alloy. Bad ass. I will post the recipe for the guides...interference fit and temperature in the am.

If you get valves from SI get seats from SI as well.

If you are not getting a new cam....and if you are not that adept at tuning D-jet.... stick with stock valve size or at worst 1.8L size valves....but both of those may narrow your choices.

More in theam. Ray

Green626 · Post by **Green626** » Wed Sep 06, 2023 9:18 pm

Ray, Thank you so much for adding to to conversation - At this point I want to keep it a 1.7 and utilize D Jet - I will make time an take pictures of cam lobs - unless needed I am not ready to split the case - My near team goal is to do a refresh keeping things relatively stock 1.7 so i car on the road. since the engine is out I am fixing mile hell hole rust, replacing right engine shelf, battery tray support. as well as partial trunk floor replacement -
Nick

Post by **Piledriver** » Wed Sep 06, 2023 10:54 pm

I must point out that Ray induced my Megasquirt addiction by mailing me one that almost worked and one still in kit form... now i have 5.

I must ALSO point out that many "djet issues" are a worthless and weak wire in the harness from the factory, and iffy connectors. Both are curable.

Green626 · Post by **Green626** » Thu Sep 07, 2023 5:33 am

I will do my best for a close inspection of my FI harness as well as grounds and vacuum lines. The car is really very original and not been tinkered with. Want to establish a base line before make changes.

Green626 · Post by **Green626** » Thu Sep 07, 2023 10:16 am

Gents
Here are pics of cam lobes and lifter let me know if these are good enough to make a call

Bruce.m · Post by **Bruce.m** » Thu Sep 07, 2023 1:20 pm

Does the lifter have a slight radius or is it flat / concave? If you put two together they should rock slightly and not sit flush.
From the photos they look flat.

Green626 · Post by **Green626** » Thu Sep 07, 2023 2:41 pm

The 6 of the 8 are flat 2 have a slight depression in center that you can see in the light reflection on the face
It looks like the two with slight depression correspond to the intake valves on cylinders 2 and 1

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