Bottom end checks after massive piston to valve contact.

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Newold1
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Re: Bottom end checks after massive piston to valve contact.

Post by Newold1 »

We obviously don't know all the clearance issues here with respect to stem to guide, valve to piston, etc. that one shot shows a lobe one one of the cams pretty wiped out so that took some time to wear that lobe like that.

My suspicions here are a few, one is the buckets seizing from lack of lubrication, fitment or overheat. Two is the same for valve stems to guides and three might be insufficient PTV clearance.

From that wear pattern on the camshaft lobe this problem did not just appear in a short time period. This valve train had problems developing and when they got to a failure point the valves finally hung up and started their HIP HOP impersonation dancing of the tops of the pistons at a slightly higher that normal cruise rpms.

Just some suspicions based on pics and input to this point.
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Re: Bottom end checks after massive piston to valve contact.

Post by AC sports »

integrale Evo wrote: Sun Feb 25, 2018 6:14 am
Carnut1 wrote: Sat Feb 24, 2018 8:23 am Sorry for the bad luck.
It isn't bad luck.


Is this the same engine featured here a few weeks ago or a different one?
1. Valve to piston clearance?
2. What is the relevant recent history of it?
3. What valve springs?
4. What cam lift in and ex?
5. Valve lift at TDC in & ex?
6. Had the guides been replaced? If so whose and what were they?

It doesn't look like a massive collision really, i'd check rod bearings at both ends, rods for straight and crank for the same initially moving on to the lesser likely areas.
This is another engine. But indeed the same type. I've built 12 of these in the last 2 years. The only difference with this one was the valve springs. The ones I used in this are actually around 8 lb heavier at the seat and around 10 lb more at .400.
Valve to piston 3mm on inlet and 2.5 on exh.
Valve springs are Abarth blue and yellow. The stronger of the 2 types I know of. Spring tension is as before build, no loss of tension or signs of heat anywhere.
Cam isn't too wild. 304*, 260*@0.050, 10.66mm lift.
LATDC 3.5mm inlet, 3mm exh.
The cams are new. They are a truncated nose design, that's why they look flat on top. That's how they are. I've used them before up to 8000 rpm without problems.
New bronze guides, but unknown manufacturer. May have seized. Looking for signs of harsh contact when I get a chance.

Carillo rods inspected and dead straight . Pistons are cast and seem ok bar a little displaced metal that will clean up. I'll check for cracks tomorrow and continue disassembly.
EVO that other engine is on hold right now for obvious reasons.
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Re: Bottom end checks after massive piston to valve contact.

Post by Newold1 »

I think this might come down to lubrication , clearances or heat.

My thinking on heat is obviously you are an engine builder, but you are not an engine monitor. I like you have build quite a few engines and many times the users (racers or mechanics) come into you with a badly damaged engine you have done may of and they seem very confident that "no it never overheated"!, "oil pressure was good"! and stair you right in the eye saying so. I've been there and done that!, I put heat 260 degree heat tabs in my builds and if those suckers are off and in the pan or valley (NO overheat?) I always look carefully at the oil pumps, filters and lube system especially if I did not do the pan and pump setups. I know where the issue started quickly when I see those two possibilities demonstrated.

With your slight spring pressure changes and measurement specs. , cam specs you use and find I don't think this was valve float, especially if that occured at 5500 rpms on an engine set to see 8000rpms and this was not your first rodeo on that engine.

Looking forward to hear back from you here on Speedtalk as to what you find, measure and conclude after you finish the tear down and repairs.
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Re: Bottom end checks after massive piston to valve contact.

Post by AC sports »

I'm with you on everything you say Newold. About not being an engine monitor, just the builder. ..but I was actually driving the car when it happened. Water temp gauge showed it was fine...but so what....oil pressure gauge ok...so what.... they won't tell me about any localized hot spots or that my guides clearances are closing up from an overheated valve....or many other things . I guess if we could monitor everything we wouldn't have blow ups in F1.
The guide will need to be ground down or drilled and collapsed to get out as its been deformed by the impact.
Looking for signs of contact in its bore, now it's been demolished, is not exactly going to prove much.
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Re: Bottom end checks after massive piston to valve contact.

Post by integrale Evo »

AC sports wrote: Sun Feb 25, 2018 1:18 pm
integrale Evo wrote: Sun Feb 25, 2018 6:14 am
Carnut1 wrote: Sat Feb 24, 2018 8:23 am Sorry for the bad luck.
It isn't bad luck.


Is this the same engine featured here a few weeks ago or a different one?
1. Valve to piston clearance?
2. What is the relevant recent history of it?
3. What valve springs?
4. What cam lift in and ex?
5. Valve lift at TDC in & ex?
6. Had the guides been replaced? If so whose and what were they?

It doesn't look like a massive collision really, i'd check rod bearings at both ends, rods for straight and crank for the same initially moving on to the lesser likely areas.
This is another engine. But indeed the same type. I've built 12 of these in the last 2 years. The only difference with this one was the valve springs. The ones I used in this are actually around 8 lb heavier at the seat and around 10 lb more at .400.
Valve to piston 3mm on inlet and 2.5 on exh.
Valve springs are Abarth blue and yellow. The stronger of the 2 types I know of. Spring tension is as before build, no loss of tension or signs of heat anywhere.
Cam isn't too wild. 304*, 260*@0.050, 10.66mm lift.
LATDC 3.5mm inlet, 3mm exh.
The cams are new. They are a truncated nose design, that's why they look flat on top. That's how they are. I've used them before up to 8000 rpm without problems.
New bronze guides, but unknown manufacturer. May have seized. Looking for signs of harsh contact when I get a chance.

Carillo rods inspected and dead straight . Pistons are cast and seem ok bar a little displaced metal that will clean up. I'll check for cracks tomorrow and continue disassembly.
EVO that other engine is on hold right now for obvious reasons.
European sourced off-the-shelf valve guides usually have plenty of clearance, if pressed in correctly all they need is a simple brush hone to touch them up, if they've been abused well...
What valve sizes?
I'd guess at that cam lift with modified springs you won't be having coil bind issues, but i'd check for it if you didn't before.
Did you check timing for belt slip before you dissembled it or had it slipped anyhow?
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Re: Bottom end checks after massive piston to valve contact.

Post by MadBill »

I know we've drifted form the original question re potential collateral damage, but you said all four exhausts were at least slightly bent. How about the intakes?
If they're all OK, count me as 2X for the exhaust cam timing somehow becoming retarded.
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Re: Bottom end checks after massive piston to valve contact.

Post by AC sports »

Exh timing was 2 teeth retarded. I don't think it was belt slip that caused it though. I'm pretty sure the belt jumped 2 teeth when the exhaust locked up and crank/ inlet pulled on the belt. I'm running a wider than stock belt with wider pulleys for better purchase.
Evo can you direct me to euro sources for bronze guides? These are U.S. sourced....but could be coming out of China of unsuitable material for all I know.
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Re: Bottom end checks after massive piston to valve contact.

Post by integrale Evo »

Valve sizes?
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Re: Bottom end checks after massive piston to valve contact.

Post by AC sports »

44 inlet
36 exh
Upon further investigation I'm leaning towards insufficient valve to stem clearances. I suspect the valve expanded to much and grabbed at full lift.
There are signs of stem contact. Either these guides of unknown quality closed up or my valves expanded too much for the avail clearance. On rebuild I'll run them looser. After installing I run an 8mm reamer through them then flexhone for finish.
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Re: Bottom end checks after massive piston to valve contact.

Post by MadBill »

What were you running for clearances? 0.002" is usually enough for most exhaust guides of similar diameter. I wouldn't be too quick to condemn the guide material. Running a cold engine too hard can expand the valve stems before the guides can follow.
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Re: Bottom end checks after massive piston to valve contact.

Post by Newold1 »

Well at least now you know where the problem originated. I am curious what engine type this was and for just exhaust valves to hit and not intakes, their must be separate chains or belts controlling the intake valves. Is this the case?
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Re: Bottom end checks after massive piston to valve contact.

Post by integrale Evo »

I was asking for details as I wondered if you'd had valve to valve contact, but I don't think so at those lifts and valve sizes.
I would be surprised if you have Chinese guides, I doubt they'd be interested in making 24 a year, but you never know, although it should have been apparent at the building stage and even now on the remaining undamaged four if they are too tight.
We sell valve guides made in Europe if you think you need some.
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