Head keeps blowing - advice please

[Knowledge]

I have a small block SR185 barrel which I have heavily modified to take an Aprillia reed valve in a TS-style. The head is a centre squish item. I do not fit a head gasket, but do use a non-setting jointing compound.

My remembrance day ride-out stopped before I got out the garage when I noticed the head was blowing at the joint to the barrel. This is certainly not the first time this has happened, but I carefully reface the gasket face and rebuild it in the hope that this won't happen again. But it does. Perhaps the head is distorting.

Am I missing something in the build, or should I be looking at a better small block head which is less likely to blow?

[CHRIS in MARGATE]

Would definitely face the cylinder top, the cylinder head, use a gasket with a gasket compound and torque down to at least l6 lbs/ft using long head nuts and flat washers. 20 miles and retorque.

[Adam_Winstone]

My own way to cure this would be to reface head and barrel on a surface plate (fine wet and dry on a mirror would do), then assemble with decent thick spring washers (you know, the sort that Vespa and others use on wheel rims... so that your rims don't come loose and your wheel drop off!) and the tiniest amount of silicon sealant (the stuff you use on the bath is fine).... then never worry or have it come loose again.

That said, I take it the casing end threads are OK, your studs are not made of cheese, and that your head is not crazy high compression?

Adam

PS - Yes, head distortion is also worth considering as this was a common issue with large block heads before the SIL chunky head became available.

[johnnyXS]

if its blowing that quickly it sounds like your compression ratio might be too high ,.... squish too small maybe...

What does your squish measure at the edge of the bore ?
If its less than 1.2mm you could fit a head gasket to compensate especially if you face the head as you'll be losing more squish clearance

[Knowledge]

Thanks for the replies.

I have a nice metal plate for re-facing the head and barrel, but when it was last re-quashed I faced the head on a lathe and the compression was lowered at the same time. The head should not leak if I have re-faced it. I have re-faced it every time I rebuild it, either in a lathe or on my face plate, but it wills blow eventually. I don't want it to blow at all.

The washers are some steel ones I made on my lathe: They are 3mm thick and fill the recess in the head for each stud. The nuts are Harry Barlow big Ali items. The studs are old Innocenti ones, which should have stretched by now.

The squish is 1.4mm. I use Wellseal on the top gasket face

[matthew]

If you have a lathe why not recess the cylinder into the head? Give yourself a millimetre interface and that should cure the head blowing.

[Dazts1]

Ali nuts ? These I'm not framilier with. But if your facing cylinder and head then are these not worth a look at. My experience in racing this last couple of season has shown me all the ally nuts I've tried to use really like coming loose. When MB first brought out the long nuts and stud kit I had issues with my head coming loose all the time. Apparently there was an issue with the nuts and studs not being tapped or cut correctly. I bought one of there later kit incarnations, also using big 3.5 flat washers and loctite and no head loose in 3434 mile. Not even when I checked to retorque it.

Just an idea. We know how these peds like to shake everything loose !

[Warkton Tornado No.1]

I think the advice you’ve received has all been sound apart from I’d never use a gasket, although others appear to have been more fortunate. They’ve always failed but perhaps that’s just my luck!

I’ve never used alloy nuts as I use long high tensile nuts, preferably the correct grade of stainless. I've worked in various Motorsport companies & never witnessed their use. My prejudice & ignorance makes me avoid anything that might act like a sponge!

I also ensure that I get the maximum length of thread engagement in the crankcase by drilling & tapping deeper. My preference is for V*spa cylinder studs with the long end in the crankcase with a touch of Loctite Studlock. I have Helicoil kits in various sizes so never hesitate to use them if a thread is suspect.

That gives me the confidence to torque up to 22.5 ft/lb with Copaslip on the nuts & thick, hard, plain washers.

For sealant, silicone (not Blue Hylomar. Aaargh!) or Green Hermetite.

Never, ever re-torqued in over 40 years.

Never had a leak since adopting this procedure, though spigoting is an even better option if starting from scratch.

I hope this helps...

[Knowledge]

I've taken the engine apart, and I'll give you details below. But first to deal with Matthew's comment.

I haven't recessed the head as there isn't quite enough length in the barrel now that the 60mm rod has gone in. I couldn't jack up the barrel without screwing with the port timings. I would add a bit of metal to the top of the barrel (I know a very good welder), but the proximity of the steel liner complicates this process.

Daz, I will post a photo of the nuts and washers shortly, but I have put a photo of these in Jetset Oily Rag in the past.

Back to the strip-down. The nuts appeared looser than they should have been, but three of the studs came out with the nuts. This proves that the Ali nuts were gripping the stud well enough. I think the issue might be to do with the way the stud were secured in the casing, so I am going to use some higher grade loctite on the studs, having made sure that they are seated to their full depth in the casings.

I have re-surfaced the head, and it took little effort to get it flat, so I don't think it has distorted, which turns my suspicions back to the studs coming out of the casing.

[Knowledge]

I also ensure that I get the maximum length of thread engagement in the crankcase by drilling & tapping deeper. My preference is for V*spa cylinder studs with the long end in the crankcase with a touch of Loctite Studlock. I have Helicoil kits in various sizes so never hesitate to use them if a thread is suspect.

Thanks WT1.

These are the studs I use. I was using them the other way up, but tonight I decided to turn them around and adopt the style you describe above.

[Warkton Tornado No.1]

Thanks

If you don't have M8 Helicoil kit, I'll gladly lend mine out, but simply increasing the thread engagement to something approaching 3 x D gives me the confidence to increase the head nut torque (with ferrous nuts!) but I won't browbeat you on that!

[Knowledge]

Thanks WT1. I do have a helicoil kit for M8, but I believe that the threads are good, and it should be possible to get a good grip without converting them to helicoil as the first step toward a properly sealed head.

Below is a photo of the ali nuts from Harry Barlow, with my own steel 3mm thick washers

[Knowledge]

This is the head, as it came off the engine. Not as much evidence of the blowing head as I had anticipated, though running v rich.

[Warkton Tornado No.1]

I’m going to stick my neck out again by suggesting that your engine is experiencing:

“Engineering creep in fasteners”

I know very little about the subject but suggest you might look further into the issue.

My understanding is that the deformation of the alloy nuts which occurs during the tightening up process leads to them moving subsequently during the heating/cooling as the engine is run.

My gut feeling is to always use hard fasteners lubed up with Copaslip...

[johnnyXS]

one other thing to maybe look into is the studs turning out may be due to an oil residue in the bottom of the thread holes preventing complete tightening due to the studs causing a slight hydraulic effect .
Definitely worth giving the threads and sockets a thorough flush out and thread clean with a blind tap

[Phil D]

Hi
Just wondering why the use of copaslip ?
When I did a stint fixing HGV ' s the use of copaslip or any other lube on truck wheel studs was expressly forbidden due to it affecting the true torque figure of the wheel nut .
The workshop manager and DAF trucks uk came and gave us all a lecture about the carnage when a wheel parts company with a 44 ton truck.
I'm not doubting anyone's engineering prowess it's just what we were told.

[Warkton Tornado No.1]

Post by Phil D » Wed Nov 16, 2016 3:33 pm

Hi
Just wondering why the use of copaslip ?
When I did a stint fixing HGV ' s the use of copaslip or any other lube on truck wheel studs was expressly forbidden due to it affecting the true torque figure of the wheel nut .
The workshop manager and DAF trucks uk came and gave us all a lecture about the carnage when a wheel parts company with a 44 ton truck.
I'm not doubting anyone's engineering prowess it's just what we were told.

Wheel fasteners are different & I don’t think any Automotive Manufacturer recommends the use of any lubricant these days.

However, personally I use Copaslip on my own vehicle wheel fasteners.

My understanding is that High Temperature copper (or aluminium) based pastes are not as ‘slippery’ as grease or oil & act as an aid to prevent galling as well as remaining as a dry film to aid removal, not encourage it.

My motoring comprises older cars & they are therefore old when I acquire them. In most instances, I would not be prepared to leave the wheel fasteners as I found them, dry & squealing like something out of “Deliverance” when I removed them!

If I’ve had a wheel change by anybody with a rattle gun, I remove the fasteners & re-torque @ the earliest opportunity. It’s a potential lifesaver as I discovered a whole car set of over stretched bolts & made the Local Company buy replacements.

My suspicion is that is the Industry norm & that Automotive Manufacturers are aware of the practice of ‘one high torque setting suits all’ & stipulating dry fasteners may lessen the problem of over stretching the fasteners.

BTW Knowledge, I’m only responding to a point made by another, not hijacking the thread!

Dummy.JPG

So, in the instance of cylinder head nuts, I also continue to use Copaslip for the reasons stated with the added bonus that the cylinder studs are far less likely to be unwound from the crankcase

As in "Fools & Horses" a "Little Dab'll do ya!" & my tin dates back to the days of King Arthur......Francis

[Phil D]

Thanks WT1
I'll get the wife to lube me nuts ASAP :lol:
Seriously just making an honest observation that I thought had a bearing on why nuts (wheels or any other type ) may loosen.
Had to look up "galling" though!

[Warkton Tornado No.1]

Post by Phil D » Wed Nov 16, 2016 4:54 pm

Thanks WT1
I'll get the wife to lube me nuts ASAP

Kerist! They should remain external @ all times though I understand there is a practice these days that has something to do with 'tea' & 'bagging'

[Wack]

Several things I do that seem to work as haven't had a head leak yet, Loctite the cylinder studs into the casing, flat or skim the gasket surfaces, no head gasket unless over a mm thick, dowelled head with Wellseal and Loctite on the head nuts torqued to 18.5 ft/lb.