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T4 Backfire

Posted: Fri Apr 08, 2016 5:08 am
by David Follett
Just installed and fired up a CD, Type 2, engine in my '69 Ghia. It is a 2.0L rebuilt by GEX, converted by PO with a Rabi upright cooling kit and fitted with dual Webers, headers and fabricated exhaust. Right now the engine idle is rough/uneven and when accelerated flames come out of the # 2 carb tube. I have rechecked timing and valve settings twice. Good advice from another forum suggested it may be a bent valve and to check push rod tubes and lifters. I have not yet. Compression is 112-120. Any suggestions would be appreciated.

Re: T4 Backfire

Posted: Sat Apr 09, 2016 6:11 am
by dave t
firing order?

Re: T4 Backfire

Posted: Sat Apr 09, 2016 10:33 am
by raygreenwood
Yes...Dave has a good point. But.....I would think......that if the firing order is wrong....either due to distributor being in the wrong position or spark plug wires wrong.....you would have flames coming out of more than one carb throat because timing would be off for at minimum two cylinders.

If you think about what can possibly cause this....if there are for sure no valve leaks either from a burned or bent valve......either the intake valve is opening when the combustion cycle is not quite finished.....or during part of the exhaust cycle where gases that are a bit too hot are still in play.

Part of the risk here.....is that its a GEX built engine. GEX being responsible for some of the worst engine assembly and parts combination abominations in the world. There could be a wide range of ugly things wrong.

One of the first things I would do is pull the distributor drive and make sure the engine is at TDC on #1 firing stroke.....and make sure the drive is properly installed.

Then pull the pushrods and lifters keeping them in order and inspect length and wear.

Also.....even though you have good compression......is it the same on all four?.....and have you done a leakdown test? Ray

Re: T4 Backfire

Posted: Sun Apr 10, 2016 4:33 pm
by dave t
Hey Ray you are right on all points, But mine would be the least P.I.A. !

Re: T4 Backfire

Posted: Tue Apr 12, 2016 7:24 am
by David Follett
Thank you for the reply & advice given. The more I hear about GEX makes me nervous. Wish I knew before but the price I paid for the car the engine was in was worth it. Sold car and have a maybe no good engine but do have the carbs and cooling kit.
I will do leak down test next before pulling push rods & lifters. Thanks again. Dave

Re: T4 Backfire

Posted: Sat Apr 16, 2016 7:27 pm
by Jadewombat
If it backfires in the carbs. the plug wire is out of order.

Re: T4 Backfire

Posted: Fri Apr 07, 2017 7:14 am
by David Follett
Finally after not being with the Ghia for awhile I have the backfire issue squared away. I was told by the p/o the CD engine I have was a 2.oL with hydraulic lifters. Well I now believe it has the 1700cc pistons & cylinders and it does have solid lifters. Leak down test shows about a 20% leakage at # 1 cylinder compared to maybe 5% at the other three. Also can see flame between the head and cylinder so the engine will come out and the head taken off. I do have another CD engine that has 1700 cylinders in the event I need one.
If someone can offer more advice my questions are:
Will 2000 cylinders fit this case? I believe the stroke is the same in both the CD and T4 engines.
Have not removed the head yet but I have on the other engine. There is a steel seal or shim at the bottom of those cylinders but nothing on the top. Going back together do I need the steel seal or shim at the bottom and should there be something between the head and cylinder?

Re: T4 Backfire

Posted: Mon Apr 10, 2017 11:10 am
by raygreenwood
Ok...lets slow down for a minute.

1. Look under the rocker shafts in the head and post the part 3's. The fact that its a "CD engine case"...is actually meaningless as to the true displacement of the engine. it can be a 1.7, 1.8 or 2.0.....or anything for that matter.

2. If it has 1.7L part # heads it may simply be a rebuilt 1.7L using a 2.0 case as the core.

3. NO...do NOT use the metal sealing rings. The factory had a technical bulletin decades ago about deleting these parts. The practice now is to lap the cylinder lightly into the head for mating surface with valve grinding compound. Then clean it off and re-install.

If you see flame coming out between the head and cylinder...99% of the time...unless you caught it in the first 20-30 miles of this...both the head and cylinder are now shot. It basically creates a cutting torch effect and cuts a groove in the cylinder mating surface that even welding can rarely fix because it destroys the elasticity of the metal.

4. It could be a 2.0L...using 1.7 or 1.8 heads that have been flycut larger. It could also be a 1.8L using 1.7L heads that have been flycut larger.

It could be an 1834cc or similar...using 90mm 1.7L pistons and the 72mm crank from the 2.0 (and would have some potential issues). It could also be a 1954cc engine using 1.8L cylinders and pistons with the 72mm stroke of the 2.0L.

Or half teh engine could be 1.7L and half of it 2.0L :roll: :lol:

These are all some of the asinine parts mismatch abominations that GEX is famous for.

5. When you get the head off...post pictures of the mating surface. Also, using a dial caliper, depth mic, or stainless steel ruler...measure the depth of the cylinder when the piston is at the bottom of the stroke so you can figure out what crank you have.

The rule of thumb for GEX built engines....always....is tear them down ...all the way down. Split the case and find out whats in it...whats been done right...whats been done wrong...or risk a 3000 rpm grenade on the interstate that destroys its all in one shot. Ray

Re: T4 Backfire

Posted: Thu May 18, 2017 6:56 am
by David Follett
Thank you Ray. Just had a chance to log in and read your response and advice. Excellent. As soon as I get engine out and disassembled I'll let you know what I find. Dave

Re: T4 Backfire

Posted: Wed Aug 22, 2018 2:38 pm
by David Follett
Hello Ray. Not sure if it was you who I contacted the other day on the Samba Type 4 forum. Here is short version of my contact:
It's been a little over a year since your last post to me and that long ago since I have had time to address my engine issue. R/side, pistons & Cylinders off. Number 1 cylinder looks real nasty inside. Scorched and some pit marks. Compression was about 90 & leak down with 100 psi into cylinder was around 80 psi. No visual burned or bad exhaust blow by damage to head or cylinder. However today I did notice blackness probably from an exhaust leak where header pipe is fitted to head. Putting axle grease on header flange then fitting that onto the copper seal in the head it did not seem to coat the copper seal completely. Did not torque header down and will do again. Although I thought the flame I saw was at bottom of cylinder it may have been coming down from the header/head connection. Valves & seats look ok so I want to go back together with new pistons & cylinders after I figure out if the header flange needs a little evening/polishing.
Confused about what cylinders to get and hopefully you can help.
Valves in head measure 33mm intake & 41mm exh. Raised markings on head which seem to be original are 43 in a circle and the VW logo in another, P/number 021 101 321S. Stamped in numbers are AX, GEX and an R.
Piston markings are: SPO,02, 92,98 STD, 93E178. Also a 1 3/4 in a circle and 79 in another. Cannot make out a name which may be GOYOP. Piston measures 92mm across the top. Piston stroke movement is 68-69mm and they are dished.
So, do I have a set of 92X69 mm pistons & cylinders and what would the cc rating be? The VW Without Guesswork lists my CD case, which I believe is from a '72 Type 2, as having a 66 mm stroke.
Again, any advice or information is appreciated.
Dave in Media, PA

Re: T4 Backfire

Posted: Thu Aug 30, 2018 10:20 pm
by Piledriver
PMs work best when you check them...

Re: T4 Backfire

Posted: Fri Aug 31, 2018 8:29 pm
by raygreenwood
Piledriver wrote:
Thu Aug 30, 2018 10:20 pm
PMs work best when you check them...
And....sadly rhe problem IIRC....was those damn Cali only heads with air injection ports :lol: .....classic GeX. Ray