TheSamba.com :: View topic - Sounds like exhaust leak...now top end replacement

Wed Jun 24, 2020 4:45 am

I have oval port type 4 heat exchangers and since changing my stock exhaust to a VS one it pops on any deceleration. It also sounds like a tractor under load, like big exhaust leak.

I've recently had the heat exchangers off, bought a large file and improved the stubs but it's made no difference. I know how to file, I spent 3 months as an apprentice filing round bars square...then round again - you know the drill. Fitted with new annealed copper rings I'm confident. Same with exhaust flanges. No sign of leaks when dismantled, a good fit.

With a length of hose for a stethoscope I can't detect any leaks. I've used this method with easy success before on leaks that sounded much less serious than this.

It has 104mm pistons, 1700 heads were adapted, light rods, stock everything else.

So the question is what sounds like a BIG exhaust leak but isn't an exhaust leak and unless it's a coincidence was caused by changing the exhaust. At that point I hadn't disturbed the heat exchangers.

Wed Jun 24, 2020 6:15 am

My 1700 type 4 had a cracked head that snapped pretty loud. It was cracked in the exhaust port.

Thu Jun 25, 2020 12:06 am

oprn wrote: My 1700 type 4 had a cracked head that snapped pretty loud. It was cracked in the exhaust port. That is my worry.
Any more educated guesses?
I may have to refit the stock exhaust, maybe there's a problem with the VS one which I would hate to find after stripping the engine and removing the heads...though I'd do that in a flash if I had somewhere better to work than a sloped stone car park. Quite annoying, I've been close to that last week as one thing led to another and I replaced the flywheel.

Is there any way an inlet manifold leak could cause my problem?

Thu Jun 25, 2020 3:15 am

oprn wrote: My 1700 type 4 had a cracked head that snapped pretty loud. It was cracked in the exhaust port.
I've double checked the compression, 175-185 psi on all 4 which all got there in 3 compressions.
I think I'd be loosing some compression for the racket it makes under
even moderate load if I had a cracked exhaust port. Sounds great free revving in neutral.

At idle speed there is a once every 4 minor change in the exhaust note and I tried to home in on by adjusting mixtures but without success.

I changed the oil and emptied the filter, all very clean, no sheen, hardly blackened. I'm calling cam and followers good after this and the compression test.

I'm running out of ideas.

Thu Jun 25, 2020 3:34 am

I used a piece of brake metal tubing connected to a piece of vacuum hose as a stethoscope , the metal tube doesn't melt ! I was looking for an exhaust leak , my ports are large with custom stubs , I was also looking for leaks between the head and cylinder .
The leak I had was a porous hole in the port just below the seat . I took the head off twice thinking I had a leaky head .

Have tried blocking the tail pipes with a rag and listening for leaks ? another old school way is to dribble some ATF oil or brake fluid down the carby throat and look for where the smoke comes put . ( Need good neighbours and a windy day !)

I'd put the old system back on and see if the popping goes away . Another place to listen is down the spark plug hole in the tinware and check for head leaks .

Thu Jun 25, 2020 3:41 am

Thanks wreck. Nasty hole!
I'm using a piece of 1/2" oil hose, perhaps I need to refine my stethoscope. :)

While planning for the worst I noticed AA are selling their own cast type-4 heads for a few hundred dollars less than the AMC versions.

I wonder if anyone on this type-1 biased forum has any experience of these AA cast heads?

Thu Jun 25, 2020 4:12 am

yeah the little 3/16 tube can get poked in small places , The porous head was fixed with a wedge of aluminium and maniseal . 3 years ago .

The AA 2lt 914 heads are good . They are just a copy of the 914 head . It's a shame they didn't put a more modern combustion chamber and make a few small changes . I've a friend building and engine with them at the moment and have scene them in person .

Before you head down that track I'd put the old exhaust on first ,if you can't find a leak somewhere .

Thu Jun 25, 2020 5:58 am

Wreck wrote: yeah the little 3/16 tube can get poked in small places , The porous head was fixed with a wedge of aluminium and maniseal . 3 years ago .

The AA 2lt 914 heads are good . They are just a copy of the 914 head . It's a shame they didn't put a more modern combustion chamber and make a few small changes . I've a friend building and engine with them at the moment and have scene them in person .

Before you head down that track I'd put the old exhaust on first ,if you can't find a leak somewhere . Oh yes definitely not ready to quit on the heads yet. Not so much the money but the time it would be out of action waiting for delivery and then ccing etc.

I was looking at these, the ones without the spark plug moved. The cheapest 42 x 36!
https://aapistons.com/collections/cylinder-heads-c...eads-42x36

Thu Jun 25, 2020 9:30 am

A quick blip.

A bit rushed and I pressed start a few seconds late, but in each location I blocked the exhaust with a rag for a few seconds.
I'd already done the test for much longer before video. I don't think it sounds too bad? I'm not hearing exhaust leaks? Blocking the exhaust as best I could had no effect on the revs.

Tomorrow I'll video driving noises, maybe do that second one ahain taking more time.

Edit, actually I can hear a tink tink tink leak I think, second head? Tinnitus. :roll:

Thu Jun 25, 2020 10:41 am

This has worked for me to find exhaust leaks. Take a shop vac and reverse it so it blows. Put it in the exhaust tip with a rag. Turn it on and hold it there and then spray all the joint with a water/soap mixture. If there is a leak it will bubble.

Thu Jun 25, 2020 11:23 am

74 Thing wrote: This has worked for me to find exhaust leaks. Take a shop vac and reverse it so it blows. Put it in the exhaust tip with a rag. Turn it on and hold it there and then spray all the joint with a water/soap mixture. If there is a leak it will bubble.
Thanks, great idea...not easy to arrange in a car park but maybe possible.

Thu Jun 25, 2020 2:43 pm

it's only a few bolts for the muffler , I'd put the old one on and just go for a drive . You've only had the issue since putting the VS one on . Yes I think the 42 or 44 ,36 AA heads are a fair price . Not Type 1 prices yet but not that far off .

I'd like to change the old heads on mine at some stage and would go for either the 42 or 44 intake valve head .

Thu Jun 25, 2020 8:06 pm

If by any chance you forgot to delete the head gaskets...this is also what a burned through head gasket can sound like on a type 4. Ray

Thu Jun 25, 2020 10:24 pm

raygreenwood wrote: If by any chance you forgot to delete the head gaskets...this is also what a burned through head gasket can sound like on a type 4. Ray
No head gaskets, 104mm pistons though so head leaks are a possibility, but I have 175-185psi compression.

Thu Jun 25, 2020 11:01 pm

Can you do a leak down test,? Compression test may not show up due to it being dynamic

Thu Jun 25, 2020 11:30 pm

66brm wrote: Can you do a leak down test,? Compression test may not show up due to it being dynamic Can't do a leak down test, local garage doesn't have one and I'm working in a car park. Not easy to access some things that were easy before the virus thing. Before I'd have assisted, now I'd be sent away and I'm not up for leaving my precious motor in the hands of a local monkey out of my sight.

Sun Jun 28, 2020 6:58 am

Wreck wrote: it's only a few bolts for the muffler , I'd put the old one on and just go for a drive . You've only had the issue since putting the VS one on .
Yes, very easy. The rain stopped, I switched back to the stock muffler, no popping. It's loud if I put my foot down but doesn't sound like an exhaust leak.
With the VS...
If I was to accelerate in 3rd to say 3500rpm then let off it wouldn't pop for about 5 seconds, then increasingly more and more, down into second, popped even more.

Around town below 30, cruising, pops straight away if I take my foot off.

Mon Jun 29, 2020 5:55 am

Should I give up on the VS exhaust or is it bad tuning the VS exhaust is revealing?

I have AFR and a new sensor, my third one. I was hoping to stop the popping before I fit the sensor, thinking it would be bad for the sensor?

Things I tried:
DRLA 40s
Reduced idles from 57 to 53. From previous this will still be on the rich side driving stacks out. No change. I tend to set idle mix 1/4 turn rich. Not tried leaning it.
Idle timing 7.5BTDC, but it's popping on higher revs than idle. Maybe more timing would help? Foot off gas there won't be any vacuum advance. It's a 205S with pertronix 1 and a flame thrower coil. The HT leads are...cheap and fairly horrible but have nice new caps on them. Plugs and gaps are stock. Plugs not fouled, heat band in the right place on all four.
The throttle plates are almost closed, 1/2 turn for idle 850rpm

I'm assuming my compression tester is inaccurate, it used to measure them 15-20psi lower and though new then, could already have been faulty, but they are all similar readings at whatever psi it really is.

Wed Jul 01, 2020 2:04 am

This is driving me nuts. I found this general pic from when I re-torqued the heads. If I zoom in on the barrel/head join there are "smudges " that shouldn't be there?

Sounds like this...

1/2 head would be easier to get off, but those sooty looking smudges...

Wed Jul 01, 2020 3:32 am

That's why I was suggesting a leak down test to pressurise the cylinder and possibly find a leaking head/cylinder seal. If it's left too long it'll cut your head like an oxy/acetylene torch.