355 Leakdown Test question

If you are at TDC with the cam marks lined up with the marks on the cam caps you need to rotate the engine 360 degrees to get to TDC on the compression stroke for cylinder #1.

The you will need to check that for each cylinder you are at TDC on the compression stroke and so on.

 

Bad advice. Wrong.

Start with all 4 camshafts lined up at the assembly marks. That is your Number 1 TDC for leak down testing. Even if the engine is out for 2 months, cold, you should be able to get less than 10% leak down. Turn the crank 90 degrees, and follow the firing order to test the next cylinder.

It helps to have a second person holding the crank steady while you apply air pressure so that it does not accidentally turn the crank ... disastrously.

If anyone cylinder is more than 20% leak down, you should consider a valve job.

 

Before a valve job wouldn't it be a good idea to use a top end cleaner to get rid of the carbon deposits on the valves? These things run rich after all. Or is it a waste?

 

You are correct.

 

Unfortunately sounds like toast.

 

Yeah, doesn't sound good. You can remove the throttle body and get a pretty good look at the valves but I'm guessing it's coming apart.

 

Cyl 1 and Cyl 2 for whatver reason seem to have the bad valve guides. At this point, your heads are done. Plan for a valve job, with valve replacement. Possibly also liner replacement for Cyl 1. You cannot tell for sure until the head is off.

Sorry for the bad news.

 

You can "repair" it by doing the one head. It is sometimes done if budget is tight. But you need to replace ALL the valve guides on that head, at least all the valves of Cyl 1. Also inspect for the need to replace that liner,

However, people who drive Ferraris are ticklers for doing it right so more often than not both heads are removed, inspected, valve job performed, all valve guides are replaced, some valves are replaced, and reassembled. Find a machine shop that can perform valve job on a 355. Probably not every shop in Texas can do this.

 

Listen to mitchell! Also, do some reading here. There are a bunch of reasons this happens to the 355 more than any other ferrari. In short putting a race motor in a car (1st production car with 100hp/L) where everything is marginal does not make for typical streetcar reliability. Your valves got to where they are by a combo of poor internal components valve guides, header quality, poor electronics, and failed mixture control. When you get the hard parts sorted with quality valves and guides make sure to address the other contributing factors in the system for future painfree enjoyment at peak performance. The 355 is a great car just not well executed.

 

There are plenty of answers on these pages. It has all been dicussed before. The synopsis is you have to have the conditions for good mixture control that means right spark and right fuel. We assume the ECU does its thing but it is a computer so garbage in garbage out. We need to have good wiring which is a shatstorm all to itself. Some think ferrari wiring is great. Others like me think it is the second coming of Lucas. Do your research there and decide for yourself. I'm on the side of refreshing every connector on the wiring harness from ECU plug to every sensor with whatever pins of your choosing. Then you have to have good fueling capability. I think the fuel injector wiring harness should be completely redone and fuel injectors cleaned and balanced with new parts as needed during every 5 year service. The concept of routine FI maintenance is new on these pages perhaps in the last 5 years. Go back 10 years and people only talked about it when there were problems. Now you will find posts by surprised owners who send injectors in for routine clean and get back damning reports of how lame their injector function was and they did not know it. Use a quality outfit to clean injectors like RC engineering as opposed to the guy who just forces cleaner through them. RC changes out all the parts like catch screens and o-rings and can fix bad pintles and properly identify a bad injector for replacement. RC was the innovator of injector service some 50 years ago. You have plenty on your plate to get your heads back. You will have plenty of time to research some of the topics I have talked about here and decide for yourself how far you want to take it. Some guys polish their 355's and drive 200 miles a year. Fixing the one valve might be fine for those guys. Some guys are exclusively tracking their 355's constantly improving their personal race track driving abilities and they need 100% 355 as Ferrari envisioned.

 

I had my heads re-done on my 348 as I had a timing slip issue and bent all the valves. I re-assembled and did a leak down. 6 cylinders were 1-2% but 2 of them were as you describe, I could hear air just gushing from the intake. I assumed I somehow bent some valves during timing procedure. *&^%$%^^&&&*(()%$#$%$#$%% SON OF a BEOTCH!

So I pulled it apart and sent heads back to machine shop, same one. Went in person and discussed my issue. Well regarded, been doing head service for Tri-State Ferrari dealers since the 70's. Olsen Engines, I think he retired now unfortunately. https://www.yelp.com/biz_photos/olsen-engines-nyack

Anyhow, Charlie over the next few weeks took them all back down, measured the valve stems and checked seating, stem length's, seating pressure, clearance etc. I did all new guides and seals too btw. The report back was there were in fact no bent valves, everything was exactly in spec how he left it the first time. However 2 intake pistons did have some gasket or other material pressed between the seat and valve preventing seating properly.

Lesson, blow out the cylinder heads with high pressure air and nozzle from the intake runner and exhaust port with each valve open, intake and exhaust, make sure the head and valve seats are clear. Reassembled, blew them out this time, did leak down, cold with no oil 1-2 % leak down at 90psi.

You could have an issue with those specific cylinders not closing, carbon or other material may affect seating. BTW, when I pulled my heads off, there is no way some of those valves were sealing especially on 5-6 bore, they were crusted with carbon. Seems prior owners were probably short shifting and lugging the motor afraid to spin it or something. I mean you could physically see the valves not seating fully relative to others with the plain naked eye. All that would needed was some seafoam treatment perhaps, alas they were bent, so out with the old in with the new!

Put a scope down the intake and check for carbon or debris.

Good luck!

 

I would get eyes on the valves and seats with a borescope before tearing down the engine. '99 has the upgraded guides from the factory, and at only 35k miles it'd be unusual (though of course not the least bit impossible) to have bad guides. Maybe there is carbon on the seat. Maybe it sat at one point and there's rust. Only takes a few mins to verify before you go all-in.

 

An italian tune up does not fix everything but it does not cost anything to try.

 

The fact that you were able to get the number down 30% by just spraying some PB blaster in there tells me that the guides are not likely the culprit. I would keep trying to get those numbers down before dumping boatloads of dough on a repair that may not be necessary, BTW did you do a compression test before taking the engine out? Curious to see what those numbers would look like.
OTOH I understand if you are looking for piece of mind than there probably isn't a better time to do it while the engine is out, I'm sure that many 355 heads were removed for no other logical reason than piece of mind. Like FBB said, it's a race engine that's not used for racing. If it was going to race next weekend then absolutely rip that baby down, valves/pistons/liners and on and on.

 

You have done the hard job getting the engine on the bench, pull the heads, clean and lap the valves in, measure the valve guides to see if ok. Pointless doing half a job now you have got this far

 

Use sea foam, when you get it back on the road use sea foam sucking some in the intake with a vacuum hose, take it pout for Italian tune, it will smoke like a forest fire and your neighbors will hate you but it clears off carbon alright. Started using it back on 03 before people knew what it was for.

 

I remember someone on here recommend AC Delco top end cleaner. May not be bad to look into.

 

I've always wondered about such cleaning products. Never really seen significant results on YouTube. On the other hand, I have seen the effects of a blown head gasket which typically results in a clean piston. Makes me think of those water injection devices that were sold in the 60's and 70's that were suppose to improve performance. Maybe we should be spraying coolant into the cylinders to clean them???

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Good way to wash the oil off the liners and wreck the engine

 

Well shouldn't be any oil above the rings and water should not be able to get below them. Don't know how that translates into a wrecked engine.